[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32
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. Cc: Joe Jin <joe.jin@xxxxxxxxxx> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx> --- Changed since v1: - Add commit message to explain why xen_hvm_init_time_ops() is delayed for any vcpus. (Suggested by Boris Ostrovsky) - Add a comment in xen_hvm_smp_prepare_boot_cpu() referencing the related code in xen_hvm_guest_init(). (suggested by Juergen Gross) Changed since v2: - Delay for all VCPUs. (Suggested by Boris Ostrovsky) - Add commit message that why PVM is not supported by this patch - Test if kexec/kdump works with mainline xen (HVM and PVM) Changed since v3: - Re-use v2 but move the login into xen_hvm_init_time_ops() (Suggested by Boris Ostrovsky) arch/x86/xen/smp_hvm.c | 6 ++++++ arch/x86/xen/time.c | 25 ++++++++++++++++++++++++- 2 files changed, 30 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c index 6ff3c887e0b9..b70afdff419c 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 diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c index 55b3407358a9..dcf292cc859e 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -558,16 +558,36 @@ 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 * available. */ if (!xen_have_vector_callback) - return; + goto exit; if (!xen_feature(XENFEAT_hvm_safe_pvclock)) { pr_info("Xen doesn't support pvclock on HVM, disable pv timer"); + goto exit; + } + + /* + * 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; } @@ -577,6 +597,9 @@ void __init xen_hvm_init_time_ops(void) x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents; x86_platform.set_wallclock = xen_set_wallclock; + +exit: + hvm_time_initialized = true; } #endif -- 2.17.1
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