From nobody Fri Dec 19 19:03:08 2025 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 8CC8C2FF66D; Tue, 14 Oct 2025 01:11:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760404275; cv=none; b=MwOEccmzy+Lyo3rnZR2qgZZNhJGazgaobrn6s1XYu2CCifWqH/pMkIKyKG/6s/GtRpH20bv1MCW4r7S2QZe9YZVW+KWh4SAjYQsOEaW+WdAYjZDklJ4heqIDKohi5vwlvA/eOfL5YSs5Fk6WtHeSQgDny6X2nq8wKoKiU9s0MUA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760404275; c=relaxed/simple; bh=IFsZ/jOQWWW3xwkxbu3WCd4BvXBkkfrqDLXO3MVgDWc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jX/cX5Tms55/8XAc3ZVz0e/qBGcApMSSjZtEBcRa0E0huyHcXakMz9ic5S/O7hXekOUKm3kT2SXflx3eTZQU3B3SgCQ25iTGtCOHZEMtnCXRrsIGSCECkIAk/RwARhqCDJd22abDg2/X9v2NGggFQfnZ8zSIEnKenqqBlszZZ04= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=HQwZ5aop; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="HQwZ5aop" Received: from terminus.zytor.com (terminus.zytor.com [IPv6:2607:7c80:54:3:0:0:0:136]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 59E19p1a1568441 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 13 Oct 2025 18:10:07 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 59E19p1a1568441 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025092201; t=1760404208; bh=TfIz7rhAUjyw9R1P12vK4v753WTLFiHdQ6L7wjZZXn4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HQwZ5aoppyqqWorEVCmuxAipw2O7yGgxDGdpQeVzmeaMlkV6ctwJhuYg2aXaBqiTR IdQs7ERPmCiL+FxjY465UPlSwnpU0WNl/3qyFgVwqRtfrYW0qWdz0DpB6/guL1Bwo2 ZuQkK4ldyehLev34xaDRUhiEHFURecngYE8WFvZhVX4WX4rUnFBbpRKkTAsiUhw0hx dDab4JJUm88T+NHjyJ65vr8yKO49RHpygTJ2wqoZRpdFnpexpTPzwruvpX9Dubk6Ux qTLT12ZsGcRxmcYb8T2Ju8sZNmZ0e9pKUSEZStkek7YeYyUfat6M8SBpPjUX1us4xA xpr4ov+BgQQMg== From: "Xin Li (Intel)" To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org Cc: pbonzini@redhat.com, seanjc@google.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, xin@zytor.com, luto@kernel.org, peterz@infradead.org, andrew.cooper3@citrix.com, chao.gao@intel.com, hch@infradead.org Subject: [PATCH v8 13/21] KVM: x86: Save/restore the nested flag of an exception Date: Mon, 13 Oct 2025 18:09:42 -0700 Message-ID: <20251014010950.1568389-14-xin@zytor.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251014010950.1568389-1-xin@zytor.com> References: <20251014010950.1568389-1-xin@zytor.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 Content-Type: text/plain; charset="utf-8" Save/restore the nested flag of an exception during VM save/restore and live migration to ensure a correct event stack level is chosen when a nested exception is injected through FRED event delivery. Signed-off-by: Xin Li (Intel) Tested-by: Xuelian Guo --- Change in v8: * Update KVM_CAP_EXCEPTION_NESTED_FLAG, as the number in v7 is used by another new cap. Change in v5: * Add TB from Xuelian Guo. Change in v4: * Add live migration support for exception nested flag (Chao Gao). --- Documentation/virt/kvm/api.rst | 21 ++++++++++++++++++++- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/include/uapi/asm/kvm.h | 4 +++- arch/x86/kvm/x86.c | 19 ++++++++++++++++++- include/uapi/linux/kvm.h | 1 + 5 files changed, 43 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 6ae24c5ca559..68e425a97e7c 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -1184,6 +1184,10 @@ The following bits are defined in the flags field: fields contain a valid state. This bit will be set whenever KVM_CAP_EXCEPTION_PAYLOAD is enabled. =20 +- KVM_VCPUEVENT_VALID_NESTED_FLAG may be set to inform that the + exception is a nested exception. This bit will be set whenever + KVM_CAP_EXCEPTION_NESTED_FLAG is enabled. + - KVM_VCPUEVENT_VALID_TRIPLE_FAULT may be set to signal that the triple_fault_pending field contains a valid state. This bit will be set whenever KVM_CAP_X86_TRIPLE_FAULT_EVENT is enabled. @@ -1283,6 +1287,10 @@ can be set in the flags field to signal that the exception_has_payload, exception_payload, and exception.pending fields contain a valid state and shall be written into the VCPU. =20 +If KVM_CAP_EXCEPTION_NESTED_FLAG is enabled, KVM_VCPUEVENT_VALID_NESTED_FL= AG +can be set in the flags field to inform that the exception is a nested +exception and exception_is_nested shall be written into the VCPU. + If KVM_CAP_X86_TRIPLE_FAULT_EVENT is enabled, KVM_VCPUEVENT_VALID_TRIPLE_F= AULT can be set in flags field to signal that the triple_fault field contains a valid state and shall be written into the VCPU. @@ -8678,7 +8686,7 @@ given VM. When this capability is enabled, KVM resets the VCPU when setting MP_STATE_INIT_RECEIVED through IOCTL. The original MP_STATE is preserved. =20 -7.43 KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED +7.44 KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED ------------------------------------------- =20 :Architectures: arm64 @@ -8689,6 +8697,17 @@ This capability indicate to the userspace whether a = PFNMAP memory region can be safely mapped as cacheable. This relies on the presence of force write back (FWB) feature support on the hardware. =20 +7.45 KVM_CAP_EXCEPTION_NESTED_FLAG +---------------------------------- + +:Architectures: x86 +:Parameters: args[0] whether feature should be enabled or not + +With this capability enabled, an exception is save/restored with the +additional information of whether it was nested or not. FRED event +delivery uses this information to ensure a correct event stack level +is chosen when a VM entry injects a nested exception. + 8. Other capabilities. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_hos= t.h index 3b6dadf368eb..5fff22d837aa 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1491,6 +1491,7 @@ struct kvm_arch { bool has_mapped_host_mmio; bool guest_can_read_msr_platform_info; bool exception_payload_enabled; + bool exception_nested_flag_enabled; =20 bool triple_fault_event; =20 diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kv= m.h index d420c9c066d4..fbeeea236fc2 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -331,6 +331,7 @@ struct kvm_reinject_control { #define KVM_VCPUEVENT_VALID_SMM 0x00000008 #define KVM_VCPUEVENT_VALID_PAYLOAD 0x00000010 #define KVM_VCPUEVENT_VALID_TRIPLE_FAULT 0x00000020 +#define KVM_VCPUEVENT_VALID_NESTED_FLAG 0x00000040 =20 /* Interrupt shadow states */ #define KVM_X86_SHADOW_INT_MOV_SS 0x01 @@ -368,7 +369,8 @@ struct kvm_vcpu_events { struct { __u8 pending; } triple_fault; - __u8 reserved[26]; + __u8 reserved[25]; + __u8 exception_is_nested; __u8 exception_has_payload; __u64 exception_payload; }; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9b3e60c0628e..1d247734dd87 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4968,6 +4968,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, lon= g ext) case KVM_CAP_GET_MSR_FEATURES: case KVM_CAP_MSR_PLATFORM_INFO: case KVM_CAP_EXCEPTION_PAYLOAD: + case KVM_CAP_EXCEPTION_NESTED_FLAG: case KVM_CAP_X86_TRIPLE_FAULT_EVENT: case KVM_CAP_SET_GUEST_DEBUG: case KVM_CAP_LAST_CPU: @@ -5713,6 +5714,7 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct= kvm_vcpu *vcpu, events->exception.error_code =3D ex->error_code; events->exception_has_payload =3D ex->has_payload; events->exception_payload =3D ex->payload; + events->exception_is_nested =3D ex->nested; =20 events->interrupt.injected =3D vcpu->arch.interrupt.injected && !vcpu->arch.interrupt.soft; @@ -5738,6 +5740,8 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct= kvm_vcpu *vcpu, | KVM_VCPUEVENT_VALID_SMM); if (vcpu->kvm->arch.exception_payload_enabled) events->flags |=3D KVM_VCPUEVENT_VALID_PAYLOAD; + if (vcpu->kvm->arch.exception_nested_flag_enabled) + events->flags |=3D KVM_VCPUEVENT_VALID_NESTED_FLAG; if (vcpu->kvm->arch.triple_fault_event) { events->triple_fault.pending =3D kvm_test_request(KVM_REQ_TRIPLE_FAULT, = vcpu); events->flags |=3D KVM_VCPUEVENT_VALID_TRIPLE_FAULT; @@ -5752,7 +5756,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct = kvm_vcpu *vcpu, | KVM_VCPUEVENT_VALID_SHADOW | KVM_VCPUEVENT_VALID_SMM | KVM_VCPUEVENT_VALID_PAYLOAD - | KVM_VCPUEVENT_VALID_TRIPLE_FAULT)) + | KVM_VCPUEVENT_VALID_TRIPLE_FAULT + | KVM_VCPUEVENT_VALID_NESTED_FLAG)) return -EINVAL; =20 if (events->flags & KVM_VCPUEVENT_VALID_PAYLOAD) { @@ -5767,6 +5772,13 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct= kvm_vcpu *vcpu, events->exception_has_payload =3D 0; } =20 + if (events->flags & KVM_VCPUEVENT_VALID_NESTED_FLAG) { + if (!vcpu->kvm->arch.exception_nested_flag_enabled) + return -EINVAL; + } else { + events->exception_is_nested =3D 0; + } + if ((events->exception.injected || events->exception.pending) && (events->exception.nr > 31 || events->exception.nr =3D=3D NMI_VECTOR)) return -EINVAL; @@ -5792,6 +5804,7 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct = kvm_vcpu *vcpu, vcpu->arch.exception.error_code =3D events->exception.error_code; vcpu->arch.exception.has_payload =3D events->exception_has_payload; vcpu->arch.exception.payload =3D events->exception_payload; + vcpu->arch.exception.nested =3D events->exception_is_nested; =20 vcpu->arch.interrupt.injected =3D events->interrupt.injected; vcpu->arch.interrupt.nr =3D events->interrupt.nr; @@ -6912,6 +6925,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, kvm->arch.exception_payload_enabled =3D cap->args[0]; r =3D 0; break; + case KVM_CAP_EXCEPTION_NESTED_FLAG: + kvm->arch.exception_nested_flag_enabled =3D cap->args[0]; + r =3D 0; + break; case KVM_CAP_X86_TRIPLE_FAULT_EVENT: kvm->arch.triple_fault_event =3D cap->args[0]; r =3D 0; diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 6efa98a57ec1..c7d0b6ce1a33 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -963,6 +963,7 @@ struct kvm_enable_cap { #define KVM_CAP_RISCV_MP_STATE_RESET 242 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243 #define KVM_CAP_GUEST_MEMFD_MMAP 244 +#define KVM_CAP_EXCEPTION_NESTED_FLAG 245 =20 struct kvm_irq_routing_irqchip { __u32 irqchip; --=20 2.51.0