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A spinlock can be interrupted while spinning, so make sure we preserve
the previous lock of interest if we're taking a lock from within an
interrupt handler.
We also need to deal with the case where the blocking path gets
interrupted between testing to see if the lock is free and actually
blocking. If we get interrupted there and end up in the state where
the lock is free but the irq isn't pending, then we'll block
indefinitely in the hypervisor. This fix is to make sure that any
nested lock-takers will always leave the irq pending if there's any
chance the outer lock became free.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The standard ticket spinlocks are very expensive in a virtual
environment, because their performance depends on Xen's scheduler
giving vcpus time in the order that they're supposed to take the
spinlock.
This implements a Xen-specific spinlock, which should be much more
efficient.
The fast-path is essentially the old Linux-x86 locks, using a single
lock byte. The locker decrements the byte; if the result is 0, then
they have the lock. If the lock is negative, then locker must spin
until the lock is positive again.
When there's contention, the locker spin for 2^16[*] iterations waiting
to get the lock. If it fails to get the lock in that time, it adds
itself to the contention count in the lock and blocks on a per-cpu
event channel.
When unlocking the spinlock, the locker looks to see if there's anyone
blocked waiting for the lock by checking for a non-zero waiter count.
If there's a waiter, it traverses the per-cpu "lock_spinners"
variable, which contains which lock each CPU is waiting on. It picks
one CPU waiting on the lock and sends it an event to wake it up.
This allows efficient fast-path spinlock operation, while allowing
spinning vcpus to give up their processor time while waiting for a
contended lock.
[*] 2^16 iterations is threshold at which 98% locks have been taken
according to Thomas Friebel's Xen Summit talk "Preventing Guests from
Spinning Around". Therefore, we'd expect the lock and unlock slow
paths will only be entered 2% of the time.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <clameter@linux-foundation.org>
Cc: Petr Tesarik <ptesarik@suse.cz>
Cc: Virtualization <virtualization@lists.linux-foundation.org>
Cc: Xen devel <xen-devel@lists.xensource.com>
Cc: Thomas Friebel <thomas.friebel@amd.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
fix:
arch/x86/xen/built-in.o: In function `set_page_prot':
enlighten.c:(.text+0x111d): undefined reference to `xen_raw_printk'
arch/x86/xen/built-in.o: In function `xen_start_kernel':
: undefined reference to `xen_raw_console_write'
arch/x86/xen/built-in.o: In function `xen_start_kernel':
: undefined reference to `xen_raw_console_write'
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Copy 64-bit definitions of various interface structures into place.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
add xen_timer_resume() hook.
Timer resume should be done after event channel is resumed.
add xen_arch_resume() hook when ipi becomes usable after resume.
After resume, some cpu specific resource must be reinitialized
on ia64 that can't be set by another cpu.
However available hooks is run once on only one cpu so that ipi has
to be used.
During stop_machine_run() ipi can't be used because interrupt is masked.
So add another hook after stop_machine_run().
Another approach might be use resume hook which is run by
device_resume(). However device_resume() may be executed on
suspend error recovery path.
So it is necessary to determine whether it is executed on real resume path
or error recovery path.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Xen has a pte update function which will update a pte while preserving
its accessed and dirty bits. This means that ptep_modify_prot_start() can be
implemented as a simple read of the pte value. The hardware may
update the pte in the meantime, but ptep_modify_prot_commit() updates it while
preserving any changes that may have happened in the meantime.
The updates in ptep_modify_prot_commit() are batched if we're currently in lazy
mmu mode.
The mmu_update hypercall can take a batch of updates to perform, but
this code doesn't make particular use of that feature, in favour of
using generic multicall batching to get them all into the hypervisor.
The net effect of this is that each mprotect pte update turns from two
expensive trap-and-emulate faults into they hypervisor into a single
hypercall whose cost is amortized in a batched multicall.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This patch updates the xen guest to use the pvclock structs
and helper functions.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Define recently added XEN_ELFNOTEs, and use them appropriately.
Most significantly, this enables domain checkpointing (xm save -c).
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
-tip testing found the following build breakage:
drivers/built-in.o: In function `xen_suspend':
manage.c:(.text+0x4390f): undefined reference to `xen_console_resume'
with this config:
http://redhat.com/~mingo/misc/config-Thu_May_29_09_23_16_CEST_2008.bad
i have bisected it down to:
| commit 0e91398f2a
| Author: Jeremy Fitzhardinge <jeremy@goop.org>
| Date: Mon May 26 23:31:27 2008 +0100
|
| xen: implement save/restore
the problem is that drivers/xen/manage.c is built unconditionally if
CONFIG_XEN is enabled and makes use of xen_suspend(), but
drivers/char/hvc_xen.c, where the xen_suspend() method is implemented,
is only build if CONFIG_HVC_XEN=y as well.
i have solved this by providing a NOP implementation for xen_suspend()
in the !CONFIG_HVC_XEN case.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Hook into the device model to make sure that timekeeping's resume handler
is called. This deals with our clocksource's non-monotonicity over the
save/restore. Explicitly call clock_has_changed() to make sure that
all the timers get retriggered properly.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This patch implements Xen save/restore and migration.
Saving is triggered via xenbus, which is polled in
drivers/xen/manage.c. When a suspend request comes in, the kernel
prepares itself for saving by:
1 - Freeze all processes. This is primarily to prevent any
partially-completed pagetable updates from confusing the suspend
process. If CONFIG_PREEMPT isn't defined, then this isn't necessary.
2 - Suspend xenbus and other devices
3 - Stop_machine, to make sure all the other vcpus are quiescent. The
Xen tools require the domain to run its save off vcpu0.
4 - Within the stop_machine state, it pins any unpinned pgds (under
construction or destruction), performs canonicalizes various other
pieces of state (mostly converting mfns to pfns), and finally
5 - Suspend the domain
Restore reverses the steps used to save the domain, ending when all
the frozen processes are thawed.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add code to:
1. Deal with the console page being canonicalized. During save, the
console's mfn in the start_info structure is canonicalized to a pfn.
In order to deal with that, we always use a copy of the pfn and
indirect off that all the time. However, we fall back to using the
mfn if the pfn hasn't been initialized yet.
2. Restore the console event channel, and rebind it to the existing irq.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add rebind_evtchn_irq(), which will rebind an device driver's existing
irq to a new event channel on restore. Since the new event channel
will be masked and bound to vcpu0, we update the state accordingly and
unmask the irq once everything is set up.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add xen handles realted definitions for xen memory which ia64/xen needs.
Pointer argumsnts for ia64/xen hypercall are passed in pseudo physical
address (guest physical address) so that it is required to convert
guest kernel virtual address into pseudo physical address.
The xen guest handle represents such arguments.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The pvfb backend indicates dynamic mode support by creating node
feature_resize with a non-zero value in its xenstore directory.
xen-fbfront sends a resize notification event on mode change. Fully
backwards compatible both ways.
Framebuffer size and initial resolution can be controlled through
kernel parameter xen_fbfront.video. The backend enforces a separate
size limit, which it advertises in node videoram in its xenstore
directory.
xen-kbdfront gets the maximum screen resolution from nodes width and
height in the backend's xenstore directory instead of hardcoding it.
Additional goodie: support for larger framebuffers (512M on a 64-bit
system with 4K pages).
Changing the number of bits per pixels dynamically is not supported,
yet.
Ported from
http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/92f7b3144f41http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/bfc040135633
Signed-off-by: Pat Campbell <plc@novell.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add a couple of functions which can write directly to the Xen console
for debugging. This output ends up on the host's dom0 console
(assuming it allows the domain to write there).
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The balloon driver allows memory to be dynamically added or removed from the domain,
in order to allow host memory to be balanced between multiple domains.
This patch introduces the Xen balloon driver, though it currently only
allows a domain to be shrunk from its initial size (and re-grown back to
that size). A later patch will add the ability to grow a domain beyond
its initial size.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This is a pair of Xen para-virtual frontend device drivers:
drivers/video/xen-fbfront.c provides a framebuffer, and
drivers/input/xen-kbdfront provides keyboard and mouse.
The backends run in dom0 user space.
The two drivers are not in two separate patches, because the
intermediate step (one driver, not the other) is somewhat problematic:
the backend in dom0 needs both drivers, and will refuse to complete
device initialization unless they're both present.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
When the xen block frontend driver is built as a module the module load
is only synchronous up to the point where the frontend and the backend
become connected rather than when the disk is added.
This means that there can be a race on boot between loading the module and
loading the dm-* modules and doing the scan for LVM physical volumes (all
in the initrd). In the failure case the disk is not present until after the
scan for physical volumes is complete.
Taken from:
http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/11483a00c017
Signed-off-by: Christian Limpach <Christian.Limpach@xensource.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Frontends are expected to write their protocol ABI to xenstore. Since
the protocol ABI defaults to the backend's native ABI, things work
fine without that as long as the frontend's native ABI is identical to
the backend's native ABI. This is not the case for xen-blkfront
running 32-on-64, because its ABI differs between 32 and 64 bit, and
thus needs this fix.
Based on http://xenbits.xensource.com/xen-unstable.hg?rev/c545932a18f3
and http://xenbits.xensource.com/xen-unstable.hg?rev/ffe52263b430 by
Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <Jeremy.Fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
On xen/ia64 and xen/powerpc hypercall arguments are passed by pseudo
physical address (guest physical address) so that it's necessary to
convert from virtual address into pseudo physical address. The frame
work is called xencomm.
Import arch generic part of xencomm.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
split out x86 specific part from grant-table.c and
allow ia64/xen specific initialization.
ia64/xen grant table is based on pseudo physical address
(guest physical address) unlike x86/xen. On ia64 init_mm
doesn't map identity straight mapped area.
ia64/xen specific grant table initialization is necessary.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Don't use alloc_vm_area()/free_vm_area() directly, instead define
xen_alloc_vm_area()/xen_free_vm_area() and use them.
alloc_vm_area()/free_vm_area() are used to allocate/free area which
are for grant table mapping. Xen/x86 grant table is based on virtual
address so that alloc_vm_area()/free_vm_area() are suitable.
On the other hand Xen/ia64 (and Xen/powerpc) grant table is based on
pseudo physical address (guest physical address) so that allocation
should be done differently.
The original version of xenified Linux/IA64 have its own
allocate_vm_area()/free_vm_area() definitions which don't allocate vm area
contradictory to those names.
Now vanilla Linux already has its definitions so that it's impossible
to have IA64 definitions of allocate_vm_area()/free_vm_area().
Instead introduce xen_allocate_vm_area()/xen_free_vm_area() and use them.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The definitions in include/asm/xen/page.h are arch specific.
ia64/xen wants to define its own version. So move them to arch specific
directory and keep include/xen/page.h in order not to break compilation.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Define resend_irq_on_evtchn() which ia64/xen uses.
Although it isn't used by current x86/xen code, it's arch generic
so that put it into common code.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Remove x86 dependency in drivers/xen/events.c for ia64/xen support
introducing include/asm/xen/events.h.
Introduce xen_irqs_disabled() to hide regs->flags
Introduce xen_do_IRQ() to hide regs->orig_ax.
make enum ipi_vector definition arch specific. ia64/xen needs four vectors.
Add one rmb() because on ia64 xchg() isn't barrier.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
move arch/x86/xen/events.c undedr drivers/xen to share codes
with x86 and ia64. And minor adjustment to compile.
ia64/xen also uses events.c
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add xen handles realted definitions for xen vcpu which ia64/xen needs.
Pointer argumsnts for ia64/xen hypercall are passed in pseudo physical
address (guest physical address) so that it is required to convert
guest kernel virtual address into pseudo physical address.
The xen guest handle represents such arguments.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add xen handles realted definitions for grant table which ia64/xen
needs.
Pointer argumsnts for ia64/xen hypercall are passed in pseudo physical
address (guest physical address) so that it is required to convert
guest kernel virtual address into pseudo physical address right before
issuing hypercall.
The xen guest handle represents such arguments.
Define necessary handles and helper functions.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add xen VIRQ numbers defined for arch specific use.
ia64/xen domU uses VIRQ_ARCH_0 for virtual itc timer.
Although all those constants aren't used yet by ia64
at this moment, add all arch specific VIRQ numbers.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Add xen hypercall numbers defined for arch specific use.
ia64/xen domU uses __HYPERVISOR_arch_1 to manipulate paravirtualized
IOSAPIC. Although all those constants aren't used yet by IA64 at this
moment, add all arch specific hypercall numbers.
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Xen's pte operations on mfns can be unified like the kernel's pfn operations.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Make sure pte_t, whatever its definition, has a pte element with type
pteval_t. This allows common code to access it without needing to be
specifically parameterised on what pagetable mode we're compiling for.
For 32-bit, this means that pte_t becomes a union with "pte" and "{
pte_low, pte_high }" (PAE) or just "pte_low" (non-PAE).
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
The kernel's copy of struct vcpu_register_vcpu_info was out of date,
at best causing the hypercall to fail and the guest kernel to fall
back to the old mechanism, or worse, causing random memory corruption.
[ Stable folks: applies to 2.6.23 ]
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Stable Kernel <stable@kernel.org>
Cc: Morten =?utf-8?q?B=C3=B8geskov?= <xen-users@morten.bogeskov.dk>
Cc: Mark Williamson <mark.williamson@cl.cam.ac.uk>
Fix:
linux/include/xen/page.h: In function mfn_pte:
linux/include/xen/page.h:149: error: __supported_pte_mask undeclared (first use in this function)
linux/include/xen/page.h:149: error: (Each undeclared identifier is reported only once
linux/include/xen/page.h:149: error: for each function it appears in.)
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
An experimental patch for Xen allows guests to place their vcpu_info
structs anywhere. We try to use this to place the vcpu_info into the
PDA, which allows direct access.
If this works, then switch to using direct access operations for
irq_enable, disable, save_fl and restore_fl.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>
This communicates with the machine control software via a registry
residing in a controlling virtual machine. This allows dynamic
creation, destruction and modification of virtual device
configurations (network devices, block devices and CPUS, to name some
examples).
[ Greg, would you mind giving this a review? Thanks -J ]
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Greg KH <greg@kroah.com>
Add Xen 'grant table' driver which allows granting of access to
selected local memory pages by other virtual machines and,
symmetrically, the mapping of remote memory pages which other virtual
machines have granted access to.
This driver is a prerequisite for many of the Xen virtual device
drivers, which grant the 'device driver domain' restricted and
temporary access to only those memory pages that are currently
involved in I/O operations.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Implement a Xen back-end for hvc console.
* * *
Add early printk support via hvc console, enable using
"earlyprintk=xen" on the kernel command line.
From: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Olof Johansson <olof@lixom.net>
This is a fairly straightforward Xen implementation of smp_ops.
Xen has its own IPI mechanisms, and has no dependency on any
APIC-based IPI. The smp_ops hooks and the flush_tlb_others pv_op
allow a Xen guest to avoid all APIC code in arch/i386 (the only apic
operation is a single apic_read for the apic version number).
One subtle point which needs to be addressed is unpinning pagetables
when another cpu may have a lazy tlb reference to the pagetable. Xen
will not allow an in-use pagetable to be unpinned, so we must find any
other cpus with a reference to the pagetable and get them to shoot
down their references.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andi Kleen <ak@suse.de>
Xen implements interrupts in terms of event channels. Each guest
domain gets 1024 event channels which can be used for a variety of
purposes, such as Xen timer events, inter-domain events,
inter-processor events (IPI) or for real hardware IRQs.
Within the kernel, we map the event channels to IRQs, and implement
the whole interrupt handling using a Xen irq_chip.
Rather than setting NR_IRQ to 1024 under PARAVIRT in order to
accomodate Xen, we create a dynamic mapping between event channels and
IRQs. Ideally, Linux will eventually move towards dynamically
allocating per-irq structures, and we can use a 1:1 mapping between
event channels and irqs.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Eric W. Biederman <ebiederm@xmission.com>
This patch is a rollup of all the core pieces of the Xen
implementation, including:
- booting and setup
- pagetable setup
- privileged instructions
- segmentation
- interrupt flags
- upcalls
- multicall batching
BOOTING AND SETUP
The vmlinux image is decorated with ELF notes which tell the Xen
domain builder what the kernel's requirements are; the domain builder
then constructs the address space accordingly and starts the kernel.
Xen has its own entrypoint for the kernel (contained in an ELF note).
The ELF notes are set up by xen-head.S, which is included into head.S.
In principle it could be linked separately, but it seems to provoke
lots of binutils bugs.
Because the domain builder starts the kernel in a fairly sane state
(32-bit protected mode, paging enabled, flat segments set up), there's
not a lot of setup needed before starting the kernel proper. The main
steps are:
1. Install the Xen paravirt_ops, which is simply a matter of a
structure assignment.
2. Set init_mm to use the Xen-supplied pagetables (analogous to the
head.S generated pagetables in a native boot).
3. Reserve address space for Xen, since it takes a chunk at the top
of the address space for its own use.
4. Call start_kernel()
PAGETABLE SETUP
Once we hit the main kernel boot sequence, it will end up calling back
via paravirt_ops to set up various pieces of Xen specific state. One
of the critical things which requires a bit of extra care is the
construction of the initial init_mm pagetable. Because Xen places
tight constraints on pagetables (an active pagetable must always be
valid, and must always be mapped read-only to the guest domain), we
need to be careful when constructing the new pagetable to keep these
constraints in mind. It turns out that the easiest way to do this is
use the initial Xen-provided pagetable as a template, and then just
insert new mappings for memory where a mapping doesn't already exist.
This means that during pagetable setup, it uses a special version of
xen_set_pte which ignores any attempt to remap a read-only page as
read-write (since Xen will map its own initial pagetable as RO), but
lets other changes to the ptes happen, so that things like NX are set
properly.
PRIVILEGED INSTRUCTIONS AND SEGMENTATION
When the kernel runs under Xen, it runs in ring 1 rather than ring 0.
This means that it is more privileged than user-mode in ring 3, but it
still can't run privileged instructions directly. Non-performance
critical instructions are dealt with by taking a privilege exception
and trapping into the hypervisor and emulating the instruction, but
more performance-critical instructions have their own specific
paravirt_ops. In many cases we can avoid having to do any hypercalls
for these instructions, or the Xen implementation is quite different
from the normal native version.
The privileged instructions fall into the broad classes of:
Segmentation: setting up the GDT and the GDT entries, LDT,
TLS and so on. Xen doesn't allow the GDT to be directly
modified; all GDT updates are done via hypercalls where the new
entries can be validated. This is important because Xen uses
segment limits to prevent the guest kernel from damaging the
hypervisor itself.
Traps and exceptions: Xen uses a special format for trap entrypoints,
so when the kernel wants to set an IDT entry, it needs to be
converted to the form Xen expects. Xen sets int 0x80 up specially
so that the trap goes straight from userspace into the guest kernel
without going via the hypervisor. sysenter isn't supported.
Kernel stack: The esp0 entry is extracted from the tss and provided to
Xen.
TLB operations: the various TLB calls are mapped into corresponding
Xen hypercalls.
Control registers: all the control registers are privileged. The most
important is cr3, which points to the base of the current pagetable,
and we handle it specially.
Another instruction we treat specially is CPUID, even though its not
privileged. We want to control what CPU features are visible to the
rest of the kernel, and so CPUID ends up going into a paravirt_op.
Xen implements this mainly to disable the ACPI and APIC subsystems.
INTERRUPT FLAGS
Xen maintains its own separate flag for masking events, which is
contained within the per-cpu vcpu_info structure. Because the guest
kernel runs in ring 1 and not 0, the IF flag in EFLAGS is completely
ignored (and must be, because even if a guest domain disables
interrupts for itself, it can't disable them overall).
(A note on terminology: "events" and interrupts are effectively
synonymous. However, rather than using an "enable flag", Xen uses a
"mask flag", which blocks event delivery when it is non-zero.)
There are paravirt_ops for each of cli/sti/save_fl/restore_fl, which
are implemented to manage the Xen event mask state. The only thing
worth noting is that when events are unmasked, we need to explicitly
see if there's a pending event and call into the hypervisor to make
sure it gets delivered.
UPCALLS
Xen needs a couple of upcall (or callback) functions to be implemented
by each guest. One is the event upcalls, which is how events
(interrupts, effectively) are delivered to the guests. The other is
the failsafe callback, which is used to report errors in either
reloading a segment register, or caused by iret. These are
implemented in i386/kernel/entry.S so they can jump into the normal
iret_exc path when necessary.
MULTICALL BATCHING
Xen provides a multicall mechanism, which allows multiple hypercalls
to be issued at once in order to mitigate the cost of trapping into
the hypervisor. This is particularly useful for context switches,
since the 4-5 hypercalls they would normally need (reload cr3, update
TLS, maybe update LDT) can be reduced to one. This patch implements a
generic batching mechanism for hypercalls, which gets used in many
places in the Xen code.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Ian Pratt <ian.pratt@xensource.com>
Cc: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Cc: Adrian Bunk <bunk@stusta.de>
Add Xen interface header files. These are taken fairly directly from
the Xen tree, but somewhat rearranged to suit the kernel's conventions.
Define macros and inline functions for doing hypercalls into the
hypervisor.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
