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Subject: Re: [PATCH v4 1/6] KVM: Fix leak vCPU's VMCS value into other pCPU
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Marc Zyngier <Marc.Zyngier@arm.com>, stable@vger.kernel.org
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Tue, 6 Aug 2019 01:17:27 +0200
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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