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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id r3sm9225309edi.49.2021.02.08.02.28.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Feb 2021 02:28:59 -0800 (PST) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Thomas Gleixner , Paolo Bonzini Subject: Re: [RFC PATCH] KVM: x86: Set PF_VCPU when processing IRQs to fix tick-based accounting In-Reply-To: <20210206004218.312023-1-seanjc@google.com> References: <20210206004218.312023-1-seanjc@google.com> Date: Mon, 08 Feb 2021 11:28:58 +0100 Message-ID: <87lfbyonth.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > Temporarily set PF_VCPU while processing IRQ VM-Exits so that a tick IRQ > accounts the time slice to the guest. Tick-based accounting of guest > time is currently broken as PF_VCPU is only set during the relatively > short VM-Enter sequence, which runs entirely with IRQs disabled, and IRQs > that occur in the guest are processed well after PF_VCPU is cleared. > > Keep PF_VCPU set across both VMX's processing of already-acked IRQs > (handle_exit_irqoff()) and the explicit IRQ window (SVM's processing, > plus ticks that occur immediately after VM-Exit on both VMX and SVM). > > Fixes: 87fa7f3e98a1 ("x86/kvm: Move context tracking where it belongs") > Cc: stable@vger.kernel.org > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Signed-off-by: Sean Christopherson > --- > > This is quite obnoxious, hence the RFC, but I can't think of a clever, > less ugly way to fix the accounting. > > arch/x86/kvm/x86.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index d9f931c63293..6ddf341cd755 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -9118,6 +9118,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > vcpu->mode = OUTSIDE_GUEST_MODE; > smp_wmb(); > > + /* > + * Temporarily pretend this task is running a vCPU when potentially > + * processing an IRQ exit, including the below opening of an IRQ > + * window. Tick-based accounting of guest time relies on PF_VCPU > + * being set when the tick IRQ handler runs. > + */ > + current->flags |= PF_VCPU; Should we do it only when !vtime_accounting_enabled_cpu() maybe? > static_call(kvm_x86_handle_exit_irqoff)(vcpu); > > /* > @@ -9132,6 +9139,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > ++vcpu->stat.exits; > local_irq_disable(); > kvm_after_interrupt(vcpu); > + current->flags &= ~PF_VCPU; > > if (lapic_in_kernel(vcpu)) { > s64 delta = vcpu->arch.apic->lapic_timer.advance_expire_delta; -- Vitaly