[PATCH v3 10/20] KVM: VMX: Support instruction information extension

Chang S. Bae
2026-04-28T05:26:27Z

Define the VMCS field offset for the extended instruction information.
Then, support 5-bit register indices retrieval from VMCS fields.

Note the APX enumeration alone indicates the extension is available.
However, software must not assume that previously reserved bits were zero
on older implementations.

Link: https://lore.kernel.org/7bb14722-c036-4835-8ed9-046b4e67909e@redhat.com
Link: https://lore.kernel.org/aakEsXJgO-3m2xca@google.com
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
---
V2 -> V3: Drop the data structure that matches with the field format (Sean)
---
arch/x86/include/asm/vmx.h | 2 ++
arch/x86/kvm/vmx/vmx.h | 42 +++++++++++++++++++++++++++-----------
2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 37080382df54..978cd6ac6483 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -276,6 +276,8 @@ enum vmcs_field {
PID_POINTER_TABLE_HIGH = 0x00002043,
GUEST_PHYSICAL_ADDRESS = 0x00002400,
GUEST_PHYSICAL_ADDRESS_HIGH = 0x00002401,
+ EXTENDED_INSTRUCTION_INFO = 0x00002406,
+ EXTENDED_INSTRUCTION_INFO_HIGH = 0x00002407,
VMCS_LINK_POINTER = 0x00002800,
VMCS_LINK_POINTER_HIGH = 0x00002801,
GUEST_IA32_DEBUGCTL = 0x00002802,
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 4d29d32fa87c..862a9cb4f653 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -323,9 +323,18 @@ static __always_inline unsigned long vmx_get_exit_qual(struct kvm_vcpu *vcpu)
return vt->exit_qualification;
}

+/*
+ * The APX enumeration guarantees the presence of the extended fields.
+ * The host CPUID bit alone is sufficient to rely on it.
+ */
+static inline bool vmx_instr_info_extended(void)
+{
+ return static_cpu_has(X86_FEATURE_APX);
+}
+
static inline int vmx_get_exit_qual_reg(struct kvm_vcpu *vcpu)
{
- return (vmx_get_exit_qual(vcpu) >> 8) & 0xf;
+ return (vmx_get_exit_qual(vcpu) >> 8) & (vmx_instr_info_extended() ? 0x1f : 0xf);
}

static __always_inline u32 vmx_get_intr_info(struct kvm_vcpu *vcpu)
@@ -706,20 +715,22 @@ static inline bool vmx_guest_state_valid(struct kvm_vcpu *vcpu)

void dump_vmcs(struct kvm_vcpu *vcpu);

-/* A placeholder to smoothen 64-bit extension */
static inline u64 vmx_get_instr_info(void)
{
- return vmcs_read32(VMX_INSTRUCTION_INFO);
+ return vmx_instr_info_extended() ? vmcs_read64(EXTENDED_INSTRUCTION_INFO) :
+ vmcs_read32(VMX_INSTRUCTION_INFO);
}

static inline int vmx_get_instr_info_reg(u64 instr_info)
{
- return (instr_info >> 3) & 0xf;
+ return vmx_instr_info_extended() ? (instr_info >> 16) & 0x1f :
+ (instr_info >> 3) & 0xf;
}

static inline int vmx_get_instr_info_reg2(u64 instr_info)
{
- return (instr_info >> 28) & 0xf;
+ return vmx_instr_info_extended() ? (instr_info >> 40) & 0x1f :
+ (instr_info >> 28) & 0xf;
}

static inline int vmx_get_instr_info_scaling(u64 instr_info)
@@ -729,37 +740,44 @@ static inline int vmx_get_instr_info_scaling(u64 instr_info)

static inline int vmx_get_instr_info_addr_size(u64 instr_info)
{
- return (instr_info >> 7) & 7;
+ return vmx_instr_info_extended() ? (instr_info >> 2) & 3 :
+ (instr_info >> 7) & 7;
}

static inline bool vmx_get_instr_info_is_reg(u64 instr_info)
{
- return !!(instr_info & BIT(10));
+ return vmx_instr_info_extended() ? !!(instr_info & BIT(4)) :
+ !!(instr_info & BIT(10));
}

static inline int vmx_get_instr_info_seg_reg(u64 instr_info)
{
- return (instr_info >> 15) & 7;
+ return vmx_instr_info_extended() ? (instr_info >> 7) & 7 :
+ (instr_info >> 15) & 7;
}

static inline int vmx_get_instr_info_index_reg(u64 instr_info)
{
- return (instr_info >> 18) & 0xf;
+ return vmx_instr_info_extended() ? (instr_info >> 24) & 0x1f :
+ (instr_info >> 18) & 0xf;
}

static inline bool vmx_get_instr_info_index_is_valid(u64 instr_info)
{
- return !(instr_info & BIT(22));
+ return vmx_instr_info_extended() ? !(instr_info & BIT(10)) :
+ !(instr_info & BIT(22));
}

static inline int vmx_get_instr_info_base_reg(u64 instr_info)
{
- return (instr_info >> 23) & 0xf;
+ return vmx_instr_info_extended() ? (instr_info >> 32) & 0x1f :
+ (instr_info >> 23) & 0xf;
}

static inline bool vmx_get_instr_info_base_is_valid(u64 instr_info)
{
- return !(instr_info & BIT(27));
+ return vmx_instr_info_extended() ? !(instr_info & BIT(11)) :
+ !(instr_info & BIT(27));
}

static inline bool vmx_can_use_ipiv(struct kvm_vcpu *vcpu)
--
2.51.0