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([2001:b07:6468:f312:a0f7:472a:1e7:7ef]) by smtp.gmail.com with ESMTPSA id c144sm18931831wmd.1.2019.11.11.06.46.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 06:46:54 -0800 (PST) Subject: Re: [PATCH v1 1/3] KVM: VMX: Consider PID.PIR to determine if vCPU has pending interrupts To: Joao Martins , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Liran Alon , Jag Raman References: <20191106175602.4515-1-joao.m.martins@oracle.com> <20191106175602.4515-2-joao.m.martins@oracle.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <67bca655-fea3-4b57-be3c-7dc58026b5d9@redhat.com> Date: Mon, 11 Nov 2019 15:46:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191106175602.4515-2-joao.m.martins@oracle.com> Content-Language: en-US X-MC-Unique: LFO5OSYsM2CoTk2uPiWi_A-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/11/19 18:56, Joao Martins wrote: > Commit 17e433b54393 ("KVM: Fix leak vCPU's VMCS value into other pCPU") > introduced vmx_dy_apicv_has_pending_interrupt() in order to determine > if a vCPU have a pending posted interrupt. This routine is used by > kvm_vcpu_on_spin() when searching for a a new runnable vCPU to schedule > on pCPU instead of a vCPU doing busy loop. >=20 > vmx_dy_apicv_has_pending_interrupt() determines if a > vCPU has a pending posted interrupt solely based on PID.ON. However, > when a vCPU is preempted, vmx_vcpu_pi_put() sets PID.SN which cause > raised posted interrupts to only set bit in PID.PIR without setting > PID.ON (and without sending notification vector), as depicted in VT-d > manual section 5.2.3 "Interrupt-Posting Hardware Operation". >=20 > Therefore, checking PID.ON is insufficient to determine if a vCPU has > pending posted interrupts and instead we should also check if there is > some bit set on PID.PIR. >=20 > Fixes: 17e433b54393 ("KVM: Fix leak vCPU's VMCS value into other pCPU") > Signed-off-by: Joao Martins > Signed-off-by: Liran Alon > --- > arch/x86/kvm/vmx/vmx.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) >=20 > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 31ce6bc2c371..18b0bee662a5 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -6141,7 +6141,10 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vc= pu) > =20 > static bool vmx_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu) > { > -=09return pi_test_on(vcpu_to_pi_desc(vcpu)); > +=09struct pi_desc *pi_desc =3D vcpu_to_pi_desc(vcpu); > + > +=09return pi_test_on(pi_desc) || > +=09=09!bitmap_empty((unsigned long *)pi_desc->pir, NR_VECTORS); > } > =20 > static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bi= tmap) Should we check the bitmap only if SN is false? We have a precondition that if SN is clear then non-empty PIR implies ON=3D1 (modulo the small window in vmx_vcpu_pi_load of course), so that'd be a bit faster. Paolo