From nobody Sun Jun 14 22:58:47 2026 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D22939F193 for ; Mon, 6 Apr 2026 22:54:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775516044; cv=none; b=MRNEF9OAy96i1A8DXn+HT7G9l1Nqo7ebVd3SjEGrcRLajvTOLQmHtwiE5wVqK2IV7rEphtcim+7nwI8kxBwmulMuVfpnordQQR2+sNHLSPpTnppBjnQc5SDLUYoHIqYZX0sz55JKAAzN4/ABovul6IeneMJCKIP46OycLC8UVi0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775516044; c=relaxed/simple; bh=MuoBagMWt/jDcUgfLpJaGKUrnLGqM8jeOkFxXnsMjRM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cn1R8CcANtTrFaWIvd/AaJrU8yxPkeF29O8CnBBbBIB+gjSHVIjAXwatpLwZUHPBKFe9wyLhzpLgBsgnS7TjKtyfqDAKYlDpjmnluNS5JPL1n80v5X+8Ktf/pHy2MkmzqeazDgyuHNTCoD19Ccr+hDU5ZQAP9EdM8Vy+8LhBMek= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=FnUoBFCK; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="FnUoBFCK" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-82cf8dcd079so3103987b3a.1 for ; Mon, 06 Apr 2026 15:54:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775516043; x=1776120843; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=yEGEx+La+PH+2Jiph98j/xu2MhRe4olp8x4K7K50o+s=; b=FnUoBFCKSic0cqprdMKncQlJKd5R52FDiRS0SdJZ/gmN27rGoD8VZRbFAa/rD9kc6y hidzFzMEj10YWutD7W2uLI7sctxergJP4oxNxePU1Z8avsCr7ppoa6pDpYE5ojdmd8c1 8fXBpSVs4HX4WJTlYVwvSasy/5grgpVQe23dWg2Xc4jfkHvtophz+rJpulNzh9Ynpb2/ 2H9IyNGGTnaueZxLygMRy6eHLvf6+V9rOhNM3T+ntZ9HkMlxImqsBa3qtBwpPeFL+H+0 EV3mX7LlMse2KIivU8Z2IiChtsNebuQ9YYGTGydHgHLr/+zn7+fnUeHQGfSkIGIWW76H Tt+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775516043; x=1776120843; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=yEGEx+La+PH+2Jiph98j/xu2MhRe4olp8x4K7K50o+s=; b=ICgCJ68loGND9/p1c311nzpmxWWLtNIhuifsY7Zw92vtyMFZfPk6UEcRLk8BzjAxJs DQaUZNJa1k7uWCZA9doonQqNdpbbZehT/GZJP9XGmnJpUTISdS9ZdgU3bwe2Oxynlhgj H0uwytxUr9GONc1jR1OXq/E7Ggjp1PpvY44OXH/SB8l8F9jOEU31RILNAHP8gJujI1AK cGbEWyptpxSyiClCIRaSdzrsAN3w1aGIjDPCZo7YoykuswleTCykdoqauWDa4eBNMt21 ycZK79gv+2dQfHeRMsf7VEWD5HWtebhfP8zBsTLHxf0oYAbSpyq0yRUMz5et/0dCL2Vq M9Ew== X-Forwarded-Encrypted: i=1; AJvYcCXgZRYoBzN/DMpkpFLPaosySbxdRczrKx2r8e+9SVuF6rdH3j9cdGrxgYRImFepVUe0BoJw/R+2PJTTHDE=@vger.kernel.org X-Gm-Message-State: AOJu0YzHlsI93vUqPuLgGqd03+IPjGkFARaoVKiqguvRHXhJMYZbPq7F YkvUo0G+1GxKW3vSJYT68Zl8mpXho2b2ATgINmBFVs+87vuoLDFiUlveAzSmoKKTWezZHSMVvin 1a6b6tg== X-Received: from pfbic15.prod.google.com ([2002:a05:6a00:8a0f:b0:82a:6195:3c55]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3926:b0:7f7:2f82:9904 with SMTP id d2e1a72fcca58-82d0da2c50cmr14753321b3a.5.1775516042723; Mon, 06 Apr 2026 15:54:02 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 6 Apr 2026 15:53:56 -0700 In-Reply-To: <20260406225359.1245490-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260406225359.1245490-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260406225359.1245490-2-seanjc@google.com> Subject: [PATCH v3 1/3] KVM: x86: Don't leave APF half-enabled on bad APF data GPA From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+bc0e18379a290e5edfe4@syzkaller.appspotmail.com, Xiaoyao Li , Ethan Yang Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ethan Yang kvm_pv_enable_async_pf() updates vcpu->arch.apf.msr_en_val before initializing the APF data gfn_to_hva cache. If userspace provides an invalid GPA, kvm_gfn_to_hva_cache_init() fails, but msr_en_val stays enabled and leaves APF state half-initialized. Later APF paths can then try to use the empty cache and trigger WARN_ON() in kvm_read_guest_offset_cached(). Determine the new APF enabled state from the incoming MSR value, do cache initialization first on the enable path, and commit msr_en_val only after successful initialization. Keep the disable path behavior unchanged. Reported-by: syzbot+bc0e18379a290e5edfe4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dbc0e18379a290e5edfe4 Fixes: 344d9588a9df ("KVM: Add PV MSR to enable asynchronous page faults de= livery.") Link: https://lore.kernel.org/r/aHfD3MczrDpzDX9O@google.com Suggested-by: Sean Christopherson Reviewed-by: Xiaoyao Li Signed-off-by: Ethan Yang [sean: don't bother with a local "enable" variable] Signed-off-by: Sean Christopherson Acked-by: Ethan Yang [1/3] Reviewed-by: Binbin Wu Reviewed-by: Ethan Yang [2/3] Reviewed-by: Ethan Yang [3/3] --- arch/x86/kvm/x86.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0a1b63c63d1a..c35d359b56dd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1043,11 +1043,16 @@ bool kvm_require_dr(struct kvm_vcpu *vcpu, int dr) } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_require_dr); =20 -static bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) +static bool __kvm_pv_async_pf_enabled(u64 data) { u64 mask =3D KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT; =20 - return (vcpu->arch.apf.msr_en_val & mask) =3D=3D mask; + return (data & mask) =3D=3D mask; +} + +static bool kvm_pv_async_pf_enabled(struct kvm_vcpu *vcpu) +{ + return __kvm_pv_async_pf_enabled(vcpu->arch.apf.msr_en_val); } =20 static inline u64 pdptr_rsvd_bits(struct kvm_vcpu *vcpu) @@ -3647,18 +3652,19 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *= vcpu, u64 data) if (!lapic_in_kernel(vcpu)) return data ? 1 : 0; =20 + if (__kvm_pv_async_pf_enabled(data) && + kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa, + sizeof(u64))) + return 1; + vcpu->arch.apf.msr_en_val =3D data; =20 - if (!kvm_pv_async_pf_enabled(vcpu)) { + if (!__kvm_pv_async_pf_enabled(data)) { kvm_clear_async_pf_completion_queue(vcpu); kvm_async_pf_hash_reset(vcpu); return 0; } =20 - if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa, - sizeof(u64))) - return 1; - vcpu->arch.apf.send_always =3D (data & KVM_ASYNC_PF_SEND_ALWAYS); vcpu->arch.apf.delivery_as_pf_vmexit =3D data & KVM_ASYNC_PF_DELIVERY_AS_= PF_VMEXIT; =20 --=20 2.53.0.1213.gd9a14994de-goog From nobody Sun Jun 14 22:58:47 2026 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 518533A0EA2 for ; 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Mon, 06 Apr 2026 15:54:04 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 6 Apr 2026 15:53:57 -0700 In-Reply-To: <20260406225359.1245490-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260406225359.1245490-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260406225359.1245490-3-seanjc@google.com> Subject: [PATCH v3 2/3] KVM: x86: Drop superfluous caching of KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+bc0e18379a290e5edfe4@syzkaller.appspotmail.com, Xiaoyao Li , Ethan Yang Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Drop kvm_vcpu_arch.delivery_as_pf_vmexit and instead use msr_en_val as the source of truth to reduce the probability of operating on stale data. This fixes flaws where KVM fails to update delivery_as_pf_vmexit when APF is explicitly disabled by the guest or implicitly disabled by KVM on INIT. Absent other bugs, the flaws are benign as KVM *shouldn't* consume delivery_as_pf_vmexit when PV APF support is disabled. Simply delete the field, as there's zero benefit to maintaining a separate "cache" of the state. Fixes: 52a5c155cf79 ("KVM: async_pf: Let guest support delivery of async_pf= from guest mode") Signed-off-by: Sean Christopherson Acked-by: Ethan Yang [1/3] Reviewed-by: Binbin Wu Reviewed-by: Ethan Yang [2/3] Reviewed-by: Ethan Yang [3/3] Reviewed-by: Xiaoyao Li --- arch/x86/include/asm/kvm_host.h | 1 - arch/x86/kvm/x86.c | 3 +-- 2 files changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_hos= t.h index c470e40a00aa..fae1f4aeca5a 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1039,7 +1039,6 @@ struct kvm_vcpu_arch { u32 id; u32 host_apf_flags; bool send_always; - bool delivery_as_pf_vmexit; bool pageready_pending; } apf; =20 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c35d359b56dd..4632222a5d1c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3666,7 +3666,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vc= pu, u64 data) } =20 vcpu->arch.apf.send_always =3D (data & KVM_ASYNC_PF_SEND_ALWAYS); 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Mon, 06 Apr 2026 15:54:06 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 6 Apr 2026 15:53:58 -0700 In-Reply-To: <20260406225359.1245490-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260406225359.1245490-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260406225359.1245490-4-seanjc@google.com> Subject: [PATCH v3 3/3] KVM: x86: Drop superfluous caching of KVM_ASYNC_PF_SEND_ALWAYS From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+bc0e18379a290e5edfe4@syzkaller.appspotmail.com, Xiaoyao Li , Ethan Yang Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Drop kvm_vcpu_arch.send_always and instead use msr_en_val as the source of truth to reduce the probability of operating on stale data. This fixes flaws where KVM fails to update send_always when APF is explicitly disabled by the guest or implicitly disabled by KVM on INIT. Absent other bugs, the flaws are benign as KVM *shouldn't* consume send_always when PV APF support is disabled. Simply delete the field, as there's zero benefit to maintaining a separate "cache" of the state. Opportunistically turn the enabled vs. disabled logic at the end of kvm_pv_enable_async_pf() into an if-else instead of using an early return, e.g. so that it's more obvious that both paths are "success" paths. Fixes: 6adba5274206 ("KVM: Let host know whether the guest can handle async= PF in non-userspace context.") Signed-off-by: Sean Christopherson Acked-by: Ethan Yang [1/3] Reviewed-by: Binbin Wu Reviewed-by: Ethan Yang [2/3] Reviewed-by: Ethan Yang [3/3] Reviewed-by: Xiaoyao Li --- arch/x86/include/asm/kvm_host.h | 1 - arch/x86/kvm/x86.c | 12 ++++-------- 2 files changed, 4 insertions(+), 9 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_hos= t.h index fae1f4aeca5a..2a6906597637 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1038,7 +1038,6 @@ struct kvm_vcpu_arch { u16 vec; u32 id; u32 host_apf_flags; - bool send_always; bool pageready_pending; } apf; =20 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4632222a5d1c..e24877353f17 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3659,16 +3659,12 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *= vcpu, u64 data) =20 vcpu->arch.apf.msr_en_val =3D data; =20 - if (!__kvm_pv_async_pf_enabled(data)) { + if (__kvm_pv_async_pf_enabled(data)) { + kvm_async_pf_wakeup_all(vcpu); + } else { kvm_clear_async_pf_completion_queue(vcpu); kvm_async_pf_hash_reset(vcpu); - return 0; } - - vcpu->arch.apf.send_always =3D (data & KVM_ASYNC_PF_SEND_ALWAYS); - - kvm_async_pf_wakeup_all(vcpu); - return 0; } =20 @@ -14025,7 +14021,7 @@ static bool kvm_can_deliver_async_pf(struct kvm_vcp= u *vcpu) if (!kvm_pv_async_pf_enabled(vcpu)) return false; =20 - if (!vcpu->arch.apf.send_always && + if (!(vcpu->arch.apf.msr_en_val & KVM_ASYNC_PF_SEND_ALWAYS) && (vcpu->arch.guest_state_protected || !kvm_x86_call(get_cpl)(vcpu))) return false; =20 --=20 2.53.0.1213.gd9a14994de-goog