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Trying to use a kprobe on ppc32 results in the below splat:
BUG: Unable to handle kernel data access on read at 0x7c0802a6
Faulting instruction address: 0xc002e9f0
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K PowerPC 44x Platform
Modules linked in:
CPU: 0 PID: 89 Comm: sh Not tainted 5.13.0-rc1-01824-g3a81c0495fdb #7
NIP: c002e9f0 LR: c0011858 CTR: 00008a47
REGS: c292fd50 TRAP: 0300 Not tainted (5.13.0-rc1-01824-g3a81c0495fdb)
MSR: 00009000 <EE,ME> CR: 24002002 XER: 20000000
DEAR: 7c0802a6 ESR: 00000000
<snip>
NIP [c002e9f0] emulate_step+0x28/0x324
LR [c0011858] optinsn_slot+0x128/0x10000
Call Trace:
opt_pre_handler+0x7c/0xb4 (unreliable)
optinsn_slot+0x128/0x10000
ret_from_syscall+0x0/0x28
The offending instruction is:
81 24 00 00 lwz r9,0(r4)
Here, we are trying to load the second argument to emulate_step():
struct ppc_inst, which is the instruction to be emulated. On ppc64,
structures are passed in registers when passed by value. However, per
the ppc32 ABI, structures are always passed to functions as pointers.
This isn't being adhered to when setting up the call to emulate_step()
in the optprobe trampoline. Fix the same.
Fixes: eacf4c0202654a ("powerpc: Enable OPTPROBES on PPC32")
Cc: stable@vger.kernel.org
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5bdc8cbc9a95d0779e27c9ddbf42b40f51f883c0.1624425798.git.christophe.leroy@csgroup.eu
copy-paste contains implicit "copy buffer" state that can contain
arbitrary user data (if the user process executes a copy instruction).
This could be snooped by another process if a context switch hits while
the state is live. So cp_abort is executed on context switch to clear
out possible sensitive data and prevent the leak.
cp_abort is done after the low level _switch(), which means it is never
reached by newly created tasks, so they could snoop on this buffer
between their first and second context switch.
Fix this by doing the cp_abort before calling _switch. Add some
comments which should make the issue harder to miss.
Fixes: 07d2a628bc000 ("powerpc/64s: Avoid cpabort in context switch when possible")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210622053036.474678-1-npiggin@gmail.com
To better match non booke version of SYSCALL_ENTRY macro,
interchange r1 and r11 in the booke version.
While at it, in both versions use r1 instead of r11 to save
_NIP and _CCR.
All other uses of r11 will go away in next patch, so don't
bother changing them for now.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1684c39724a069b0ce1aa82eaee6ec194e354e4e.1622818435.git.christophe.leroy@csgroup.eu
klimit is a global variable initialised at build time with the
value of _end.
This variable is never modified, so _end symbol can be used directly.
Remove klimit.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9fa9ba6807c17f93f35a582c199c646c4a8bfd9c.1622800638.git.christophe.leroy@csgroup.eu
printk_safe_flush_on_panic() has special lock breaking code for the case
where we panic()ed with the console lock held. It relies on panic IPI
causing other CPUs to mark themselves offline.
Do as most other architectures do.
This effectively reverts commit de6e5d38417e ("powerpc: smp_send_stop do
not offline stopped CPUs"), unfortunately it may result in some false
positive warnings, but the alternative is more situations where we can
crash without getting messages out.
Fixes: de6e5d38417e ("powerpc: smp_send_stop do not offline stopped CPUs")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210623041245.865134-1-npiggin@gmail.com
The caller has been moved to C after irq soft-mask state has been
reconciled, and Linux IRQs have been marked as disabled, so this no
longer needs to play games with IRQ internals.
Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210623022924.704645-1-npiggin@gmail.com
PowerVM will not arbitrarily oversubscribe or stop guests, page out the
guest kernel text to a NFS volume connected by carrier pigeon to abacus
based storage, etc., as a KVM host might. So PowerVM guests are not
likely to be killed by the hard lockup watchdog in normal operation,
even with shared processor LPARs which still get a minimum allotment of
CPU time.
Enable the hard lockup detector by default on !KVM guests, which we will
assume is PowerVM. It has been useful in finding problems on bare metal
kernels.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210623021528.702241-1-npiggin@gmail.com
The PPC_RFI_SRR_DEBUG check added by patch "powerpc/64s: avoid reloading
(H)SRR registers if they are still valid" has a few deficiencies. It
does not fix the actual problem, it's not enabled by default, and it
causes a program check interrupt which can cause more difficulties.
However there are a lot of paths which may clobber SRRs or change return
regs, and difficult to have a high confidence that all paths are covered
without wider testing.
Add a relatively low overhead always-enabled check that catches most
such cases, reports once, and fixes it so the kernel can continue.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Rebase, use switch & INT names, squash in race fix from Nick]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
prep_irq_for_user_exit() has only one caller, squash it
inside that caller.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-18-npiggin@gmail.com
prep_irq_for_user_exit() is a superset of
prep_irq_for_kernel_enabled_exit().
Rename prep_irq_for_kernel_enabled_exit() as prep_irq_for_enabled_exit()
and have prep_irq_for_user_exit() use it.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-17-npiggin@gmail.com
prep_irq_for_user_exit() is a superset of
prep_irq_for_kernel_enabled_exit(). In order to allow refactoring in
following patch, interchange the two. This will allow
prep_irq_for_user_exit() to call a renamed version of
prep_irq_for_kernel_enabled_exit().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-16-npiggin@gmail.com
interrupt_exit_user_prepare() is a superset of
interrupt_exit_user_prepare_main().
Refactor to avoid code duplication.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-15-npiggin@gmail.com
Rename syscall_exit_prepare_main() into interrupt_exit_prepare_main()
Pass it the 'ret' so that it can 'or' it directly instead of
oring twice, once inside the function and once outside.
And remove 'r3' parameter which is not used.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[np: split out some changes into other patches]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-14-npiggin@gmail.com
Use the restart table facility to return from interrupt or system calls
without disabling MSR[EE] or MSR[RI].
Interrupt return asm is put into the low soft-masked region, to prevent
interrupts being processed here, although they are still taken as masked
interrupts which causes SRRs to be clobbered, and a pending soft-masked
interrupt to require replaying.
The return code uses restart table regions to redirct to a fixup handler
rather than continue with the exit, if such an interrupt happens. In
this case the interrupt return is redirected to a fixup handler which
reloads r1 for the interrupt stack and reloads registers and sets state
up to replay the soft-masked interrupt and try the exit again.
Some types of security exit fallback flushes and barriers are currently
unable to cope with reentrant interrupts, e.g., because they store some
state in the scratch SPR which would be clobbered even by masked
interrupts. For now the interrupts-enabled exits are disabled when these
flushes are used.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Guard unused exit_must_hard_disable() as reported by lkp]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-13-npiggin@gmail.com
Treat code below __end_soft_masked as soft-masked for the purpose
of alternate return. 64s already mostly does this for scv entry.
This will be used to exit from interrupts without disabling MSR[EE].
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-12-npiggin@gmail.com
Prevent interrupt restore from allowing racing hard interrupts going
ahead of previous soft-pending ones, by using the soft-masked restart
handler to allow a store to clear the soft-mask while knowing nothing
is soft-pending.
This probably doesn't matter much in practice, but it's a simple
demonstrator / test case to exercise the restart table logic.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-11-npiggin@gmail.com
The exception table fixup adjusts a failed page fault's interrupt return
location if it was taken at an address specified in the exception table,
to a corresponding fixup handler address.
Introduce a variation of that idea which adds a fixup table for NMIs and
soft-masked asynchronous interrupts. This will be used to protect
certain critical sections that are sensitive to being clobbered by
interrupts coming in (due to using the same SPRs and/or irq soft-mask
state).
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-10-npiggin@gmail.com
This frees up one more register (and takes advantage of that to
clean things up a little bit).
This register will be used in the following patch.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-9-npiggin@gmail.com
This extends the MSR[RI]=0 window a little further into the system
call in order to pair RI and EE enabling with a single mtmsrd.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-8-npiggin@gmail.com
The next patch would like to move interrupt return assembly code to a low
location before general text, so move it into its own file and include via
head_64.S
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-7-npiggin@gmail.com
When an interrupt is taken, the SRR registers are set to return to where
it left off. Unless they are modified in the meantime, or the return
address or MSR are modified, there is no need to reload these registers
when returning from interrupt.
Introduce per-CPU flags that track the validity of SRR and HSRR
registers. These are cleared when returning from interrupt, when
using the registers for something else (e.g., OPAL calls), when
adjusting the return address or MSR of a context, and when context
switching (which changes the return address and MSR).
This improves the performance of interrupt returns.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Fold in fixup patch from Nick]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-5-npiggin@gmail.com
This makes no real difference yet except that HSRR type interrupts will
use hrfid to return. This is important for the next patch.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-4-npiggin@gmail.com
CONFIG_PPC_BOOK3S should be CONFIG_PPC_BOOK3S_64. restore_math is a
no-op for other configurations.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[np: split from another patch]
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-2-npiggin@gmail.com
Pass the value of linux_banner to firmware via option vector 7.
Option vector 7 is described in "LoPAR" Linux on Power Architecture
Reference v2.9, in table B.7 on page 824:
An ASCII character formatted null terminated string that describes
the client operating system. The string shall be human readable and
may be displayed on the console.
The string can be up to 256 bytes total, including the nul terminator.
linux_banner contains lots of information, and should make it possible
to identify the exact kernel version that is running:
const char linux_banner[] =
"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
For example:
Linux version 4.15.0-144-generic (buildd@bos02-ppc64el-018) (gcc
version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)) #148-Ubuntu SMP Sat May 8
02:32:13 UTC 2021 (Ubuntu 4.15.0-144.148-generic 4.15.18)
It's also printed at boot to the console/dmesg, which should make it
possible to correlate what firmware receives with the console/dmesg on
the machine.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210621064938.2021419-2-mpe@ellerman.id.au
In a subsequent patch we'd like to have something like a strscpy_pad()
implementation usable in prom_init.c.
Currently we have a strcpy() implementation with only one caller, so
convert it into strscpy_pad() and update the caller.
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210621064938.2021419-1-mpe@ellerman.id.au
This adds support to the Microwatt platform to use the standard
16550-style UART which available in the standalone Microwatt FPGA.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/YMwXGCTzedpQje7r@thinks.paulus.ozlabs.org
Add the arch specific insn page allocator for powerpc. This allocates
ROX pages if STRICT_KERNEL_RWX is enabled. These pages are only written
to with patch_instruction() which is able to write RO pages.
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[jpn: Reword commit message, switch to __vmalloc_node_range()]
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210609013431.9805-5-jniethe5@gmail.com
Make module_alloc() use PAGE_KERNEL protections instead of
PAGE_KERNEL_EXEX if Strict Module RWX is enabled.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210609013431.9805-4-jniethe5@gmail.com
POWER9 and POWER10 asynchronous machine checks due to stores have their
cause reported in SRR1 but SRR1[42] is set, which in other cases
indicates DSISR cause.
Check for these cases and clear SRR1[42], so the cause matching uses
the i-side (SRR1) table.
Fixes: 7b9f71f974a1 ("powerpc/64s: POWER9 machine check handler")
Fixes: 201220bb0e8c ("powerpc/powernv: Machine check handler for POWER10")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210517140355.2325406-1-npiggin@gmail.com
Merge some powerpc KVM patches from our topic branch.
In particular this brings in Nick's big series rewriting parts of the
guest entry/exit path in C.
Conflicts:
arch/powerpc/kernel/security.c
arch/powerpc/kvm/book3s_hv_rmhandlers.S
When delivering a signal to a sigaction style handler (SA_SIGINFO), we
pass pointers to the siginfo and ucontext via r4 and r5.
Currently we populate the values in those registers by reading the
pointers out of the sigframe in user memory, even though the values in
user memory were written by the kernel just prior:
unsafe_put_user(&frame->info, &frame->pinfo, badframe_block);
unsafe_put_user(&frame->uc, &frame->puc, badframe_block);
...
if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
err |= get_user(regs->gpr[4], (unsigned long __user *)&frame->pinfo);
err |= get_user(regs->gpr[5], (unsigned long __user *)&frame->puc);
ie. we write &frame->info into frame->pinfo, and then read frame->pinfo
back into r4, and similarly for &frame->uc.
The code has always been like this, since linux-fullhistory commit
d4f2d95eca2c ("Forward port of 2.4 ppc64 signal changes.").
There's no reason for us to read the values back from user memory,
rather than just setting the value in the gpr[4/5] directly. In fact
reading the value back from user memory opens up the possibility of
another user thread changing the values before we read them back.
Although any process doing that would be racing against the kernel
delivering the signal, and would risk corrupting the stack, so that
would be a userspace bug.
Note that this is 64-bit only code, so there's no subtlety with the size
of pointers differing between kernel and user. Also the frame variable
is not modified to point elsewhere during the function.
In the past reading the values back from user memory was not costly, but
now that we have KUAP on some CPUs it is, so we'd rather avoid it for
that reason too.
So change the code to just set the values directly, using the same
values we have written to the sigframe previously in the function.
Note also that this matches what our 32-bit signal code does.
Using a version of will-it-scale's signal1_threads that sets SA_SIGINFO,
this results in a ~4% increase in signals per second on a Power9, from
229,777 to 239,766.
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210610072949.3198522-1-mpe@ellerman.id.au
This implementation uses spin_until_cond in wd_smp_lock including
neither linux/processor.h nor asm/processor.h
This patch includes linux/processor.h here for spin_until_cond usage.
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5e8d2d50f301a346040362028c2ecba40685de9e.1623438544.git.christophe.leroy@csgroup.eu
PPC_TRANSACTIONAL_MEM is only on book3s/64
SPE is only on booke
PPC_TRANSACTIONAL_MEM selects ALTIVEC and VSX
Therefore, within PPC_TRANSACTIONAL_MEM sections,
ALTIVEC and VSX are always defined while SPE never is.
Remove all SPE code and all #ifdef ALTIVEC and VSX in tm
functions.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a069a348ee3c2fe3123a5a93695c2b35dc42cb40.1623340691.git.christophe.leroy@csgroup.eu
Make our stack-walking code KASAN-safe by using __no_sanitize_address.
Generic code, arm64, s390 and x86 all make accesses unchecked for similar
sorts of reasons: when unwinding a stack, we might touch memory that KASAN
has marked as being out-of-bounds. In ppc64 KASAN development, I hit this
sometimes when checking for an exception frame - because we're checking
an arbitrary offset into the stack frame.
See commit 20955746320e ("s390/kasan: avoid false positives during stack
unwind"), commit bcaf669b4bdb ("arm64: disable kasan when accessing
frame->fp in unwind_frame"), commit 91e08ab0c851 ("x86/dumpstack:
Prevent KASAN false positive warnings") and commit 6e22c8366416
("tracing, kasan: Silence Kasan warning in check_stack of stack_tracer").
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210614120907.1952321-1-dja@axtens.net
Comment says that __main() is there to make GCC happy.
It's been there since the implementation of ppc arch in Linux 1.3.45.
ppc32 is the only architecture having that. Even ppc64 doesn't have it.
Seems like GCC is still happy without it.
Drop it for good.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d01028f8166b98584eec536b52f14c5e3f98ff6b.1623172922.git.christophe.leroy@csgroup.eu
PTE_SIZE means PTE page table size in most placed, whereas
in hash_low.S in means size of one entry in the table.
Rename it PTE_T_SIZE, and define it directly in hash_low.S
instead of going through asm-offsets.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/83a008a9fd6cc3f2bbcb470f592555d260ed7a3d.1623063174.git.christophe.leroy@csgroup.eu
At the time being, empty_zero_page[] is defined in each
platform head.S.
Define it in mm/mem.c instead, and put it in BSS section instead
of the DATA section. Commit 5227cfa71f9e ("arm64: mm: place
empty_zero_page in bss") explains why it is interesting to have
it in BSS.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5838caffa269e0957c5a50cc85477876220298b0.1623063174.git.christophe.leroy@csgroup.eu
switch_mmu_context() does things that can easily be done in C.
For updating user segments, we have update_user_segments().
As mentionned in commit b5efec00b671 ("powerpc/32s: Move KUEP
locking/unlocking in C"), update_user_segments() has the loop
unrolled which is a significant performance gain.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/05c0875ad8220c03452c3a334946e207c6ca04d6.1622708530.git.christophe.leroy@csgroup.eu
