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    SubjectRe: [PATCH v4 1/6] KVM: Fix leak vCPU's VMCS value into other pCPU
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    On 05/08/19 04:03, Wanpeng Li wrote:
    > From: Wanpeng Li <wanpengli@tencent.com>
    >
    > After commit d73eb57b80b (KVM: Boost vCPUs that are delivering interrupts), a
    > five years old bug is exposed. Running ebizzy benchmark in three 80 vCPUs VMs
    > on one 80 pCPUs Skylake server, a lot of rcu_sched stall warning splatting
    > in the VMs after stress testing:
    >
    > INFO: rcu_sched detected stalls on CPUs/tasks: { 4 41 57 62 77} (detected by 15, t=60004 jiffies, g=899, c=898, q=15073)
    > Call Trace:
    > flush_tlb_mm_range+0x68/0x140
    > tlb_flush_mmu.part.75+0x37/0xe0
    > tlb_finish_mmu+0x55/0x60
    > zap_page_range+0x142/0x190
    > SyS_madvise+0x3cd/0x9c0
    > system_call_fastpath+0x1c/0x21
    >
    > swait_active() sustains to be true before finish_swait() is called in
    > kvm_vcpu_block(), voluntarily preempted vCPUs are taken into account
    > by kvm_vcpu_on_spin() loop greatly increases the probability condition
    > kvm_arch_vcpu_runnable(vcpu) is checked and can be true, when APICv
    > is enabled the yield-candidate vCPU's VMCS RVI field leaks(by
    > vmx_sync_pir_to_irr()) into spinning-on-a-taken-lock vCPU's current
    > VMCS.
    >
    > This patch fixes it by checking conservatively a subset of events.
    >
    > Cc: Paolo Bonzini <pbonzini@redhat.com>
    > Cc: Radim Krčmář <rkrcmar@redhat.com>
    > Cc: Christian Borntraeger <borntraeger@de.ibm.com>
    > Cc: Marc Zyngier <Marc.Zyngier@arm.com>
    > Cc: stable@vger.kernel.org
    > Fixes: 98f4a1467 (KVM: add kvm_arch_vcpu_runnable() test to kvm_vcpu_on_spin() loop)
    > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
    > ---
    > v3 -> v4:
    > * just test KVM_REQ_*
    > * rename the hook to apicv_has_pending_interrupt
    > * wrap with #ifdef CONFIG_KVM_ASYNC_PF
    > v2 -> v3:
    > * check conservatively a subset of events
    > v1 -> v2:
    > * checking swait_active(&vcpu->wq) for involuntary preemption
    >
    > arch/mips/kvm/mips.c | 5 +++++
    > arch/powerpc/kvm/powerpc.c | 5 +++++
    > arch/s390/kvm/kvm-s390.c | 5 +++++
    > arch/x86/include/asm/kvm_host.h | 1 +
    > arch/x86/kvm/svm.c | 6 ++++++
    > arch/x86/kvm/vmx/vmx.c | 6 ++++++
    > arch/x86/kvm/x86.c | 16 ++++++++++++++++
    > include/linux/kvm_host.h | 1 +
    > virt/kvm/arm/arm.c | 5 +++++
    > virt/kvm/kvm_main.c | 16 +++++++++++++++-
    > 10 files changed, 65 insertions(+), 1 deletion(-)
    >
    > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
    > index 2cfe839..95a4642 100644
    > --- a/arch/mips/kvm/mips.c
    > +++ b/arch/mips/kvm/mips.c
    > @@ -98,6 +98,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
    > return !!(vcpu->arch.pending_exceptions);
    > }
    >
    > +bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu)

    Using a __weak definition for the default implementation is a bit more
    concise. Queued with that change.

    Paolo

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