From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227y+bT3Yg5XiFsqLkcILPM9gd6JHxQ7GTizV8guVxh0sHl07QN62DVNCWnW0A0wMIUQr14a ARC-Seal: i=1; a=rsa-sha256; t=1518708265; cv=none; d=google.com; s=arc-20160816; b=ys4W4ZWm7CeexNJNNHjKRx1oGYB4eW8vtVv/sq7wpny8uVGzFrrtUAnvqBAh8j75CY DFNvIgd23jXIicAZozghYsqM6fg7UCnhhNjEzHWzL1QeBb95arBwlxyLidikLMpQlpv8 p38v1wX2F83GG7KDBXYXjlY9K0PovYYUspeduQuoxX69kko1RQl92z44ww/c67BZFRUX aucLZ6ZBN2h09pLBcTu+6jbX3WCBF/TKf8fmHESg1ZmSWk/gpeCFMAviOdLPyB7+GwEP DlF2yPZaF+SQ8Kbe2SyH74buk0KcUOfGCjotjy77Wf24f3UYyQojkhtmA4i9i0mX8AEE ZxXg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=Iz5Dodk/d+A++5CIfZG25EPYaK4IBf8bV2tUkDXyejQ=; b=XrRP0N135iKFYsErlN+aAgHZ/HwcGXM+WT1Rrktj89Pn63ogA9UqU57KEJhpVrA07l RGEwcxVW28m59vS7j3yNvAblb7J9YJR8t4BxkbuxIW3mhPJicOUZpu6xKGRVNNnnYsJZ 2MuaPS9kobUP9/fxbtgDdE7ZX3K3cjsjXeBqpAAlw82BgexMYvSVKzsuVRYFBxc69wEi MkmvcQ6dRXOKqqp4xpcu8z3iJhRFY+y+KLcYVb2sVbx4Dvtb7dZhq4LtV1xiOiCpMEkY hEYUcNCoDpEzvFEnkyrdwhUnj0Xxc/bdyD/cy+/Q266QTx+rQ/XHGJG7h/AuZsNPbdbP wVwg== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Liran Alon , Nikita Leshenko , Krish Sadhukhan , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Subject: [PATCH 4.4 087/108] KVM: nVMX: Fix races when sending nested PI while dest enters/leaves L2 Date: Thu, 15 Feb 2018 16:17:24 +0100 Message-Id: <20180215151234.465238851@linuxfoundation.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180215151222.267507937@linuxfoundation.org> References: <20180215151222.267507937@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1592481037885961253?= X-GMAIL-MSGID: =?utf-8?q?1592481037885961253?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Liran Alon commit 6b6977117f50d60455ace86b2d256f6fb4f3de05 upstream. Consider the following scenario: 1. CPU A calls vmx_deliver_nested_posted_interrupt() to send an IPI to CPU B via virtual posted-interrupt mechanism. 2. CPU B is currently executing L2 guest. 3. vmx_deliver_nested_posted_interrupt() calls kvm_vcpu_trigger_posted_interrupt() which will note that vcpu->mode == IN_GUEST_MODE. 4. Assume that before CPU A sends the physical POSTED_INTR_NESTED_VECTOR IPI, CPU B exits from L2 to L0 during event-delivery (valid IDT-vectoring-info). 5. CPU A now sends the physical IPI. The IPI is received in host and it's handler (smp_kvm_posted_intr_nested_ipi()) does nothing. 6. Assume that before CPU A sets pi_pending=true and KVM_REQ_EVENT, CPU B continues to run in L0 and reach vcpu_enter_guest(). As KVM_REQ_EVENT is not set yet, vcpu_enter_guest() will continue and resume L2 guest. 7. At this point, CPU A sets pi_pending=true and KVM_REQ_EVENT but it's too late! CPU B already entered L2 and KVM_REQ_EVENT will only be consumed at next L2 entry! Another scenario to consider: 1. CPU A calls vmx_deliver_nested_posted_interrupt() to send an IPI to CPU B via virtual posted-interrupt mechanism. 2. Assume that before CPU A calls kvm_vcpu_trigger_posted_interrupt(), CPU B is at L0 and is about to resume into L2. Further assume that it is in vcpu_enter_guest() after check for KVM_REQ_EVENT. 3. At this point, CPU A calls kvm_vcpu_trigger_posted_interrupt() which will note that vcpu->mode != IN_GUEST_MODE. Therefore, do nothing and return false. Then, will set pi_pending=true and KVM_REQ_EVENT. 4. Now CPU B continue and resumes into L2 guest without processing the posted-interrupt until next L2 entry! To fix both issues, we just need to change vmx_deliver_nested_posted_interrupt() to set pi_pending=true and KVM_REQ_EVENT before calling kvm_vcpu_trigger_posted_interrupt(). It will fix the first scenario by chaging step (6) to note that KVM_REQ_EVENT and pi_pending=true and therefore process nested posted-interrupt. It will fix the second scenario by two possible ways: 1. If kvm_vcpu_trigger_posted_interrupt() is called while CPU B has changed vcpu->mode to IN_GUEST_MODE, physical IPI will be sent and will be received when CPU resumes into L2. 2. If kvm_vcpu_trigger_posted_interrupt() is called while CPU B hasn't yet changed vcpu->mode to IN_GUEST_MODE, then after CPU B will change vcpu->mode it will call kvm_request_pending() which will return true and therefore force another round of vcpu_enter_guest() which will note that KVM_REQ_EVENT and pi_pending=true and therefore process nested posted-interrupt. Fixes: 705699a13994 ("KVM: nVMX: Enable nested posted interrupt processing") Signed-off-by: Liran Alon Reviewed-by: Nikita Leshenko Reviewed-by: Krish Sadhukhan [Add kvm_vcpu_kick to also handle the case where L1 doesn't intercept L2 HLT and L2 executes HLT instruction. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Radim Krčmář Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/vmx.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -4595,14 +4595,15 @@ static int vmx_deliver_nested_posted_int if (is_guest_mode(vcpu) && vector == vmx->nested.posted_intr_nv) { - /* the PIR and ON have been set by L1. */ - kvm_vcpu_trigger_posted_interrupt(vcpu); /* * If a posted intr is not recognized by hardware, * we will accomplish it in the next vmentry. */ vmx->nested.pi_pending = true; kvm_make_request(KVM_REQ_EVENT, vcpu); + /* the PIR and ON have been set by L1. */ + if (!kvm_vcpu_trigger_posted_interrupt(vcpu)) + kvm_vcpu_kick(vcpu); return 0; } return -1;