0848767dee
[ Upstream commit eed05744322da07dd7e419432dcedf3c2e017179 ]
The sched_clock() can be used very early since commit 857baa87b642
("sched/clock: Enable sched clock early"). In addition, with commit
38669ba205d1 ("x86/xen/time: Output xen sched_clock time from 0"), kdump
kernel in Xen HVM guest may panic at very early stage when accessing
&__this_cpu_read(xen_vcpu)->time as in below:
setup_arch()
-> init_hypervisor_platform()
-> x86_init.hyper.init_platform = xen_hvm_guest_init()
-> xen_hvm_init_time_ops()
-> xen_clocksource_read()
-> src = &__this_cpu_read(xen_vcpu)->time;
This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info'
embedded inside 'shared_info' during early stage until xen_vcpu_setup() is
used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address.
However, when Xen HVM guest panic on vcpu >= 32, since
xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) = NULL when
vcpu >= 32, xen_clocksource_read() on vcpu >= 32 would panic.
This patch calls xen_hvm_init_time_ops() again later in
xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is
registered when the boot vcpu is >= 32.
This issue can be reproduced on purpose via below command at the guest
side when kdump/kexec is enabled:
"taskset -c 33 echo c > /proc/sysrq-trigger"
The bugfix for PVM is not implemented due to the lack of testing
environment.
[boris: xen_hvm_init_time_ops() returns on errors instead of jumping to end]
Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220302164032.14569-3-dongli.zhang@oracle.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.