[PATCH] KVM: VMX: Formally define KVM's "0xdead" exit reason used for failed VM-Enter
From: Sean Christopherson <seanjc@google.com>
Date: 2026-09-21 23:56:58
Also in:
lkml
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
Add EXIT_REASON_UNDEFINED to track KVM's magic "0xdead" value that's used to stuff the exit reason on a failed VM-Enter so that the magic can be reused by TDX, and to make it more obvious that it's an arbitrary, KVM- defined value (though the whole "dead" thing makes it pretty darn obvious). Opportunistically add a compile-time assert to ensure the KVM-defined exit reason never collides with a "real" exit reason. No functional change intended. Cc: Xiaoyao Li <redacted> Cc: Yan Zhao <redacted> Cc: Binbin Wu <redacted> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/include/asm/vmx.h | 8 ++++++++ arch/x86/kvm/vmx/vmx.c | 4 +++- 2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 3f1b3096ff04..e49b836c7313 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h@@ -20,6 +20,14 @@ #include <asm/trapnr.h> #include <asm/vmxfeatures.h> +/* + * UNDEFINED is a KVM-defined value used to indicate that the basic exit reason + * is undefined/invalid, e.g. on VM-Fail or if TDX never attempted VM-Enter. + * The value itself is arbitrary, it just needs to not collide with a real exit + * reason. + */ +#define EXIT_REASON_UNDEFINED 0xdead + struct vmcs_hdr { u32 revision_id:31; u32 shadow_vmcs:1;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 612ab07d4100..c897dbf0e954 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c@@ -6388,6 +6388,8 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = { static const int kvm_vmx_max_exit_handlers = ARRAY_SIZE(kvm_vmx_exit_handlers); +static_assert(EXIT_REASON_UNDEFINED >= ARRAY_SIZE(kvm_vmx_exit_handlers)); + void vmx_get_exit_info(struct kvm_vcpu *vcpu, u32 *reason, u64 *info1, u64 *info2, u32 *intr_info, u32 *error_code) {
@@ -7474,7 +7476,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, vmx_enable_fb_clear(vmx); if (unlikely(vmx->fail)) { - vmx->vt.exit_reason.full = 0xdead; + vmx->vt.exit_reason.full = EXIT_REASON_UNDEFINED; goto out; }
base-commit: d4b7fb647204f0c81dfeae2d1a708e4d858e0c94 -- 2.55.0.1082.g2b9226bbc0-goog