From nobody Sat Oct 4 19:15:49 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 80447309DC8 for ; Wed, 13 Aug 2025 19:23:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755113011; cv=none; b=S3ooGKHmt6fKOhUpIET+o6c3hlOYjU7BzEDFOkXeahW1MnOhv9OY7fcgqT6kCqpJ1iNZ2nPDsvocuBuuwyLx+kWt96Udu1/MzSt+xDn9Lbo7EdYR0jcAKt0nuvXFhn1O2NrH5SreTplXfsOlCGjzrVn+sS6wgZL+C+xrrou3FPA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755113011; c=relaxed/simple; bh=WrZiC3yintwTEHzCwmrJW2sxgMlptqFr7NyVVui6y2g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RXi1UcZRZ9sjfsE3O+iiWC8QoNgoL+myX86sRamcba6c4GFuTn+ESesqum4ff2CKrO1dgeURSw73z6H+6tEyStH0mRHrf05WZKJqbDE3HSO614VUXTKAr4TSv3BbabDwqJ9mPyeo9N/8efUcNHEVfbaNsppOuyl9at+FKdq+q1Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Nb8rKPgR; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Nb8rKPgR" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755113008; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RG8e3jlgteGbX5xrgI1qpHzDVK7pfheXycxrt2lf9j4=; b=Nb8rKPgRdMLC7SJgZFkdlga42Rqun8LEB9vEv6TZcwtTM/hszoByYBvTfanAODW8mZZT68 PYUeh76cCpMewhFqnA7lDV1o7jVANHCZmy0IgOCpeGV8gdqucd1klCmk50CEHGV2v69jpU Kh7lmvAdnEQ7kO1QeQ8RQ/NUEslKNC0= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-653-GiD2sf_qM4yT4xtrwpT80w-1; Wed, 13 Aug 2025 15:23:25 -0400 X-MC-Unique: GiD2sf_qM4yT4xtrwpT80w-1 X-Mimecast-MFC-AGG-ID: GiD2sf_qM4yT4xtrwpT80w_1755113003 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C543A180034F; Wed, 13 Aug 2025 19:23:23 +0000 (UTC) Received: from intellaptop.redhat.com (unknown [10.22.81.148]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id AE788195608F; Wed, 13 Aug 2025 19:23:21 +0000 (UTC) From: Maxim Levitsky To: kvm@vger.kernel.org Cc: Sean Christopherson , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Paolo Bonzini , x86@kernel.org, Borislav Petkov , linux-kernel@vger.kernel.org, Maxim Levitsky Subject: [PATCH 3/3] KVM: x86: Fix the interaction between SMM and the asynchronous pagefault Date: Wed, 13 Aug 2025 15:23:13 -0400 Message-ID: <20250813192313.132431-4-mlevitsk@redhat.com> In-Reply-To: <20250813192313.132431-1-mlevitsk@redhat.com> References: <20250813192313.132431-1-mlevitsk@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Content-Type: text/plain; charset="utf-8" Currently a #SMI can cause KVM to drop an #APF ready event and subsequently causes the guest to never resume the task that is waiting for it. This can result in tasks becoming permanently stuck within the guest. This happens because KVM flushes the APF queue without notifying the guest of completed APF requests when the guest exits to real mode. And the SMM exit code calls kvm_set_cr0 with CR.PE =3D=3D 0, which triggers this code. It must be noted that while this flush is reasonable to do for the actual real mode entry, it is actually achieves nothing because it is too late to flush this queue on SMM exit. To fix this, avoid doing this flush altogether, and handle the real mode entry/exits in the same way KVM already handles the APIC enable/disable events: APF completion events are not injected while APIC is disabled, and once APIC is re-enabled, KVM raises the KVM_REQ_APF_READY request which causes the first pending #APF ready event to be injected prior to entry to the guest mode. This change also has the side benefit of preserving #APF events if the guest temporarily enters real mode - for example, to call firmware - although such usage should be extermery rare in modern operating systems. Signed-off-by: Maxim Levitsky --- arch/x86/kvm/x86.c | 11 +++++++---- arch/x86/kvm/x86.h | 1 + 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3d45a4cd08a4..5dfe166025bf 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1118,15 +1118,18 @@ void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsign= ed long old_cr0, unsigned lon } =20 if ((cr0 ^ old_cr0) & X86_CR0_PG) { - kvm_clear_async_pf_completion_queue(vcpu); - kvm_async_pf_hash_reset(vcpu); - /* * Clearing CR0.PG is defined to flush the TLB from the guest's * perspective. */ if (!(cr0 & X86_CR0_PG)) kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu); + + /* + * Re-check APF completion events, when the guest re-enables paging. + */ + if ((cr0 & X86_CR0_PG) && kvm_pv_async_pf_enabled(vcpu)) + kvm_make_request(KVM_REQ_APF_READY, vcpu); } =20 if ((cr0 ^ old_cr0) & KVM_MMU_CR0_ROLE_BITS) @@ -3547,7 +3550,7 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct = msr_data *msr_info) return 0; } =20 -static inline bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) +bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) { u64 mask =3D KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT; =20 diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index bcfd9b719ada..3949c938a88d 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -698,5 +698,6 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, in= t cpl, }) =20 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu); +bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu); =20 #endif --=20 2.49.0