Messages in this thread Patch in this message | | | From | Vitaly Kuznetsov <> | Subject | Re: [PATCH] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged | Date | Thu, 14 Jan 2021 14:45:10 +0100 |
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Wanpeng Li <kernellwp@gmail.com> writes:
> From: Wanpeng Li <wanpengli@tencent.com> > > The per-cpu vsyscall pvclock data pointer assigns either an element of the > static array hv_clock_boot (#vCPU <= 64) or dynamically allocated memory > hvclock_mem (vCPU > 64), the dynamically memory will not be allocated if > kvmclock vsyscall is disabled, this can result in cpu hotpluged fails in > kvmclock_setup_percpu() which returns -ENOMEM. This patch fixes it by not > assigning vsyscall pvclock data pointer if kvmclock vdso_clock_mode is not > VDSO_CLOCKMODE_PVCLOCK. > > Fixes: 6a1cac56f4 ("x86/kvm: Use __bss_decrypted attribute in shared variables") > Reported-by: Zelin Deng <zelin.deng@linux.alibaba.com> > Tested-by: Haiwei Li <lihaiwei@tencent.com> > Cc: Brijesh Singh <brijesh.singh@amd.com> > Cc: stable@vger.kernel.org#v4.19-rc5+ > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kernel/kvmclock.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index aa59374..0624290 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -296,7 +296,8 @@ static int kvmclock_setup_percpu(unsigned int cpu) > * pointers. So carefully check. CPU0 has been set up in init > * already. > */ > - if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0))) > + if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)) || > + (kvm_clock.vdso_clock_mode != VDSO_CLOCKMODE_PVCLOCK)) > return 0;
The comment above should probably be updated as it is not clear why we check kvm_clock.vdso_clock_mode here. Actually, I would even suggest we introduce a 'kvmclock_tsc_stable' global instead to avoid this indirect check.
> > /* Use the static page for the first CPUs, allocate otherwise */
Also, would it be better if we just avoid cpuhp_setup_state() call in this case? E.g. both these ideas combined (completely untested):
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index aa593743acf6..0827aef3ccb8 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -25,6 +25,7 @@ static int kvmclock __initdata = 1; static int kvmclock_vsyscall __initdata = 1; +static bool kvmclock_tsc_stable __ro_after_init = true; static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME; static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK; static u64 kvm_sched_clock_offset __ro_after_init; @@ -275,8 +276,10 @@ static int __init kvm_setup_vsyscall_timeinfo(void) return 0; flags = pvclock_read_flags(&hv_clock_boot[0].pvti); - if (!(flags & PVCLOCK_TSC_STABLE_BIT)) + if (!(flags & PVCLOCK_TSC_STABLE_BIT)) { + kvmclock_tsc_stable = false; return 0; + } kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK; #endif @@ -325,7 +328,8 @@ void __init kvmclock_init(void) return; } - if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu", + if (kvmclock_tsc_stable && + cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu", kvmclock_setup_percpu, NULL) < 0) { return; } -- Vitaly
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