diff options
author | Dongli Zhang <dongli.zhang@oracle.com> | 2022-03-02 08:40:32 -0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-15 14:18:35 +0200 |
commit | 8a7462b5211cd5b74b8815034d038e28cbd96d52 (patch) | |
tree | fe3610d0a1d64f41304803bcbb33310d2307f58c | |
parent | 3f8f3a1c10e268df53b201a344b3277e0527ae3b (diff) |
xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32
[ 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>
-rw-r--r-- | arch/x86/xen/smp_hvm.c | 6 | ||||
-rw-r--r-- | arch/x86/xen/time.c | 24 |
2 files changed, 29 insertions, 1 deletions
diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c index f8d39440b292..e5bd9eb42191 100644 --- a/arch/x86/xen/smp_hvm.c +++ b/arch/x86/xen/smp_hvm.c @@ -19,6 +19,12 @@ static void __init xen_hvm_smp_prepare_boot_cpu(void) xen_vcpu_setup(0); /* + * Called again in case the kernel boots on vcpu >= MAX_VIRT_CPUS. + * Refer to comments in xen_hvm_init_time_ops(). + */ + xen_hvm_init_time_ops(); + + /* * The alternative logic (which patches the unlock/lock) runs before * the smp bootup up code is activated. Hence we need to set this up * the core kernel is being patched. Otherwise we will have only diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c index befbdd8b17f0..4ec6c80f7687 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -547,6 +547,11 @@ static void xen_hvm_setup_cpu_clockevents(void) void __init xen_hvm_init_time_ops(void) { + static bool hvm_time_initialized; + + if (hvm_time_initialized) + return; + /* * vector callback is needed otherwise we cannot receive interrupts * on cpu > 0 and at this point we don't know how many cpus are @@ -556,7 +561,22 @@ void __init xen_hvm_init_time_ops(void) return; if (!xen_feature(XENFEAT_hvm_safe_pvclock)) { - pr_info("Xen doesn't support pvclock on HVM, disable pv timer"); + pr_info_once("Xen doesn't support pvclock on HVM, disable pv timer"); + return; + } + + /* + * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'. + * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest + * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access + * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic. + * + * The xen_hvm_init_time_ops() should be called again later after + * __this_cpu_read(xen_vcpu) is available. + */ + if (!__this_cpu_read(xen_vcpu)) { + pr_info("Delay xen_init_time_common() as kernel is running on vcpu=%d\n", + xen_vcpu_nr(0)); return; } @@ -568,6 +588,8 @@ void __init xen_hvm_init_time_ops(void) x86_platform.calibrate_tsc = xen_tsc_khz; x86_platform.get_wallclock = xen_get_wallclock; x86_platform.set_wallclock = xen_set_wallclock; + + hvm_time_initialized = true; } #endif |