From: Sean Christopherson Date: Tue, 18 Nov 2025 22:23:26 +0000 (-0800) Subject: KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath X-Git-Tag: v6.19-rc1~103^2~9^2~14 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=63669bd1d50f0b5cdb7bb390a0955b7b26821152;p=thirdparty%2Flinux.git KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath Handle Machine Checks (#MC) that happen on VM-Enter (VMX or TDX) outside of KVM's fastpath so that as much host state as possible is re-loaded before invoking the kernel's #MC handler. The only requirement is that KVM invokes the #MC handler before enabling IRQs (and even that could _probably_ be related to handling #MCs before enabling preemption). Waiting to handle #MCs until "more" host state is loaded hardens KVM against flaws in the #MC handler, which has historically been quite brittle. E.g. prior to commit 5567d11c21a1 ("x86/mce: Send #MC singal from task work"), the #MC code could trigger a schedule() with IRQs and preemption disabled. That led to a KVM hack-a-fix in commit 1811d979c716 ("x86/kvm: move kvm_load/put_guest_xcr0 into atomic context"). Note, vmx_handle_exit_irqoff() is common to VMX and TDX guests. Cc: Tony Lindgren Cc: Rick Edgecombe Cc: Jon Kohler Reviewed-by: Tony Lindgren Link: https://patch.msgid.link/20251118222328.2265758-3-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 163f854a39f25..6d41d2fc8043c 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -1063,9 +1063,6 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) if (unlikely((tdx->vp_enter_ret & TDX_SW_ERROR) == TDX_SW_ERROR)) return EXIT_FASTPATH_NONE; - if (unlikely(vmx_get_exit_reason(vcpu).basic == EXIT_REASON_MCE_DURING_VMENTRY)) - kvm_machine_check(); - trace_kvm_exit(vcpu, KVM_ISA_VMX); if (unlikely(tdx_failed_vmentry(vcpu))) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 634f591d253e7..788c9e81f2ba5 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7074,10 +7074,19 @@ void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu) if (to_vt(vcpu)->emulation_required) return; - if (vmx_get_exit_reason(vcpu).basic == EXIT_REASON_EXTERNAL_INTERRUPT) + switch (vmx_get_exit_reason(vcpu).basic) { + case EXIT_REASON_EXTERNAL_INTERRUPT: handle_external_interrupt_irqoff(vcpu, vmx_get_intr_info(vcpu)); - else if (vmx_get_exit_reason(vcpu).basic == EXIT_REASON_EXCEPTION_NMI) + break; + case EXIT_REASON_EXCEPTION_NMI: handle_exception_irqoff(vcpu, vmx_get_intr_info(vcpu)); + break; + case EXIT_REASON_MCE_DURING_VMENTRY: + kvm_machine_check(); + break; + default: + break; + } } /* @@ -7526,9 +7535,6 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) if (unlikely(vmx->fail)) return EXIT_FASTPATH_NONE; - if (unlikely((u16)vmx_get_exit_reason(vcpu).basic == EXIT_REASON_MCE_DURING_VMENTRY)) - kvm_machine_check(); - trace_kvm_exit(vcpu, KVM_ISA_VMX); if (unlikely(vmx_get_exit_reason(vcpu).failed_vmentry))