linux-kernel - Re: [PATCH] x86/kvm/pmu: Set AMD's virt PMU version to 1

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Message-ID: <aba3fd5b-e1ba-df66-2414-3f1109b68bbb@amd.com>
Date:   Wed, 8 May 2019 17:08:44 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>, LKML <linux-kernel@...r.kernel.org>
CC:     "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        "Natarajan, Janakarajan" <Janakarajan.Natarajan@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Liran Alon <liran.alon@...cle.com>,
        Mihai Carabas <mihai.carabas@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/kvm/pmu: Set AMD's virt PMU version to 1

On 5/8/19 12:02 PM, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> After commit:
> 
>   672ff6cff80c ("KVM: x86: Raise #GP when guest vCPU do not support PMU")

You should add this commit as a fixes tag. Since that commit went into 5.1
it would be worth this fix going into the 5.1 stable tree.

Thanks,
Tom

> 
> my AMD guests started #GPing like this:
> 
>   general protection fault: 0000 [#1] PREEMPT SMP
>   CPU: 1 PID: 4355 Comm: bash Not tainted 5.1.0-rc6+ #3
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>   RIP: 0010:x86_perf_event_update+0x3b/0xa0
> 
> with Code: pointing to RDPMC. It is RDPMC because the guest has the
> hardware watchdog CONFIG_HARDLOCKUP_DETECTOR_PERF enabled which uses
> perf. Instrumenting kvm_pmu_rdpmc() some, showed that it fails due to:
> 
>   if (!pmu->version)
>         return 1;
> 
> which the above commit added. Since AMD's PMU leaves the version at 0,
> that causes the #GP injection into the guest.
> 
> Set pmu->version arbitrarily to 1 and move it above the non-applicable
> struct kvm_pmu members.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
> Cc: kvm@...r.kernel.org
> Cc: Liran Alon <liran.alon@...cle.com>
> Cc: Mihai Carabas <mihai.carabas@...cle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> ---
>  arch/x86/kvm/pmu_amd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/pmu_amd.c b/arch/x86/kvm/pmu_amd.c
> index 1495a735b38e..50fa9450fcf1 100644
> --- a/arch/x86/kvm/pmu_amd.c
> +++ b/arch/x86/kvm/pmu_amd.c
> @@ -269,10 +269,10 @@ static void amd_pmu_refresh(struct kvm_vcpu *vcpu)
> 
>         pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << 48) - 1;
>         pmu->reserved_bits = 0xffffffff00200000ull;
> +       pmu->version = 1;
>         /* not applicable to AMD; but clean them to prevent any fall out */
>         pmu->counter_bitmask[KVM_PMC_FIXED] = 0;
>         pmu->nr_arch_fixed_counters = 0;
> -       pmu->version = 0;
>         pmu->global_status = 0;
>  }
> 
> --
> 2.21.0
>