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AJvYcCWJDBu3Gx5Nm/7k2TwHwIoddlHC7NC1U1XHUx23xC17J80raQ6HxtLn5jXtAyp1j4J33VuuBWTFum37AOA=@vger.kernel.org X-Gm-Message-State: AOJu0YylJ3NkXqHFLQoR7WJM1PEq4+QzNeLt2exs1RC38x/woPdKnkWg qcJyAOrWCgWZ7/E3qD8bGYUM3EYSFRt8EbniOUCK/6ZCqsiQ1cN3airLie8OzTwaGFtyZE3+KYe RfKE7qQ== X-Google-Smtp-Source: AGHT+IH4QbqgK/rjqLq7feIazM0nAtyNNAHCeByH/06YNfkwg9k7lbaoNX81vVU/L2yD55+9XIqmw/waN38= X-Received: from pgac7.prod.google.com ([2002:a05:6a02:2947:b0:b36:36f4:9862]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:914f:b0:23d:659c:aadd with SMTP id adf61e73a8af0-23dadeb68c0mr7268679637.22.1753817628625; Tue, 29 Jul 2025 12:33:48 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 29 Jul 2025 12:33:36 -0700 In-Reply-To: <20250729193341.621487-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250729193341.621487-1-seanjc@google.com> X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250729193341.621487-2-seanjc@google.com> Subject: [PATCH 1/5] KVM: Never clear KVM_REQ_VM_DEAD from a vCPU's requests From: Sean Christopherson To: Marc Zyngier , Oliver Upton , Sean Christopherson , Paolo Bonzini Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Adrian Hunter , Vishal Annapurve , Xiaoyao Li , Rick Edgecombe , Nikolay Borisov Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use kvm_test_request() instead of kvm_check_request() when querying KVM_REQ_VM_DEAD, i.e. don't clear KVM_REQ_VM_DEAD, as the entire purpose of KVM_REQ_VM_DEAD is to prevent the vCPU from enterring the guest ever again, even if userspace insists on redoing KVM_RUN. Ensuring KVM_REQ_VM_DEAD is never cleared will allow relaxing KVM's rule that ioctls can't be invoked on dead VMs, to only disallow ioctls if the VM is bugged, i.e. if KVM hit a KVM_BUG_ON(). Opportunistically add compile-time assertions to guard against clearing KVM_REQ_VM_DEAD through the standard APIs. Signed-off-by: Sean Christopherson --- arch/arm64/kvm/arm.c | 2 +- arch/x86/kvm/mmu/mmu.c | 2 +- arch/x86/kvm/vmx/tdx.c | 2 +- arch/x86/kvm/x86.c | 2 +- include/linux/kvm_host.h | 9 +++++++-- 5 files changed, 11 insertions(+), 6 deletions(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index f946926716b0..2fdc48c0fc4d 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1013,7 +1013,7 @@ static int kvm_vcpu_suspend(struct kvm_vcpu *vcpu) static int check_vcpu_requests(struct kvm_vcpu *vcpu) { if (kvm_request_pending(vcpu)) { - if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) + if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu)) return -EIO; =20 if (kvm_check_request(KVM_REQ_SLEEP, vcpu)) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 6e838cb6c9e1..d09bd236a92d 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4915,7 +4915,7 @@ int kvm_tdp_map_page(struct kvm_vcpu *vcpu, gpa_t gpa= , u64 error_code, u8 *level if (signal_pending(current)) return -EINTR; =20 - if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) + if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu)) return -EIO; =20 cond_resched(); diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 66744f5768c8..3e0d4edee849 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -2010,7 +2010,7 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *= vcpu) if (kvm_vcpu_has_events(vcpu) || signal_pending(current)) break; =20 - if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) { + if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu)) { ret =3D -EIO; break; } diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a1c49bc681c4..1700df68f12a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10649,7 +10649,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) bool req_immediate_exit =3D false; =20 if (kvm_request_pending(vcpu)) { - if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) { + if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu)) { r =3D -EIO; goto out; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 15656b7fba6c..627054d27222 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2261,13 +2261,18 @@ static inline bool kvm_test_request(int req, struct= kvm_vcpu *vcpu) return test_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests); } =20 -static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu) +static __always_inline void kvm_clear_request(int req, struct kvm_vcpu *vc= pu) { + BUILD_BUG_ON(req =3D=3D KVM_REQ_VM_DEAD); + clear_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests); } =20 -static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu) +static __always_inline bool kvm_check_request(int req, struct kvm_vcpu *vc= pu) { + /* Once a VM is dead, it needs to stay dead. */ + BUILD_BUG_ON(req =3D=3D KVM_REQ_VM_DEAD); + if (kvm_test_request(req, vcpu)) { kvm_clear_request(req, vcpu); =20 --=20 2.50.1.552.g942d659e1b-goog