[PATCH v8 11/21] KVM: VMX: Virtualize FRED event_data

Xin Li (Intel)
2025-10-14T01:11:14Z

Set injected-event data when injecting a #PF, #DB, or #NM caused
by extended feature disable using FRED event delivery, and save
original-event data for being used as injected-event data.

Unlike IDT using some extra CPU register as part of an event
context, e.g., %cr2 for #PF, FRED saves a complete event context
in its stack frame, e.g., FRED saves the faulting linear address
of a #PF into the event data field defined in its stack frame.

Thus a new VMX control field called injected-event data is added
to provide the event data that will be pushed into a FRED stack
frame for VM entries that inject an event using FRED event delivery.
In addition, a new VM exit information field called original-event
data is added to store the event data that would have saved into a
FRED stack frame for VM exits that occur during FRED event delivery.
After such a VM exit is handled to allow the original-event to be
delivered, the data in the original-event data VMCS field needs to
be set into the injected-event data VMCS field for the injection of
the original event.

Signed-off-by: Xin Li <xin3.li@intel.com>
[ Sean: reworked event data injection for nested ]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
---

Change in v5:
* Add TB from Xuelian Guo.

Change in v3:
* Rework event data injection for nested (Chao Gao & Sean Christopherson).

Changes in v2:
* Document event data should be equal to CR2/DR6/IA32_XFD_ERR instead
of using WARN_ON() (Chao Gao).
* Zero event data if a #NM was not caused by extended feature disable
(Chao Gao).
---
arch/x86/include/asm/kvm_host.h | 3 ++-
arch/x86/include/asm/vmx.h | 4 ++++
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 22 ++++++++++++++++++----
arch/x86/kvm/x86.c | 16 +++++++++++++++-
5 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 43a18e265289..550a8716a227 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -760,6 +760,7 @@ struct kvm_queued_exception {
u32 error_code;
unsigned long payload;
bool has_payload;
+ u64 event_data;
};

/*
@@ -2230,7 +2231,7 @@ void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr);
void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, unsigned long payload);
void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned int nr,
- bool has_error_code, u32 error_code);
+ bool has_error_code, u32 error_code, u64 event_data);
void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
void kvm_inject_emulated_page_fault(struct kvm_vcpu *vcpu,
struct x86_exception *fault);
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 6f8b8947c60c..539af190ad3e 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -269,8 +269,12 @@ enum vmcs_field {
PID_POINTER_TABLE_HIGH = 0x00002043,
SECONDARY_VM_EXIT_CONTROLS = 0x00002044,
SECONDARY_VM_EXIT_CONTROLS_HIGH = 0x00002045,
+ INJECTED_EVENT_DATA = 0x00002052,
+ INJECTED_EVENT_DATA_HIGH = 0x00002053,
GUEST_PHYSICAL_ADDRESS = 0x00002400,
GUEST_PHYSICAL_ADDRESS_HIGH = 0x00002401,
+ ORIGINAL_EVENT_DATA = 0x00002404,
+ ORIGINAL_EVENT_DATA_HIGH = 0x00002405,
VMCS_LINK_POINTER = 0x00002800,
VMCS_LINK_POINTER_HIGH = 0x00002801,
GUEST_IA32_DEBUGCTL = 0x00002802,
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 153c12dbf3eb..f52bfc69fff7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4099,7 +4099,7 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)

kvm_requeue_exception(vcpu, vector,
exitintinfo & SVM_EXITINTINFO_VALID_ERR,
- error_code);
+ error_code, 0);
break;
}
case SVM_EXITINTINFO_TYPE_INTR:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f797e6b12721..b2fd4842157c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1860,6 +1860,9 @@ void vmx_inject_exception(struct kvm_vcpu *vcpu)

vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);

+ if (is_fred_enabled(vcpu))
+ vmcs_write64(INJECTED_EVENT_DATA, ex->event_data);
+
vmx_clear_hlt(vcpu);
}

@@ -7280,7 +7283,8 @@ static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
static void __vmx_complete_interrupts(struct kvm_vcpu *vcpu,
u32 idt_vectoring_info,
int instr_len_field,
- int error_code_field)
+ int error_code_field,
+ int event_data_field)
{
u8 vector;
int type;
@@ -7315,13 +7319,17 @@ static void __vmx_complete_interrupts(struct kvm_vcpu *vcpu,
fallthrough;
case INTR_TYPE_HARD_EXCEPTION: {
u32 error_code = 0;
+ u64 event_data = 0;

if (idt_vectoring_info & VECTORING_INFO_DELIVER_CODE_MASK)
error_code = vmcs_read32(error_code_field);
+ if (is_fred_enabled(vcpu))
+ event_data = vmcs_read64(event_data_field);

kvm_requeue_exception(vcpu, vector,
idt_vectoring_info & VECTORING_INFO_DELIVER_CODE_MASK,
- error_code);
+ error_code,
+ event_data);
break;
}
case INTR_TYPE_SOFT_INTR:
@@ -7339,7 +7347,8 @@ static void vmx_complete_interrupts(struct vcpu_vmx *vmx)
{
__vmx_complete_interrupts(&vmx->vcpu, vmx->idt_vectoring_info,
VM_EXIT_INSTRUCTION_LEN,
- IDT_VECTORING_ERROR_CODE);
+ IDT_VECTORING_ERROR_CODE,
+ ORIGINAL_EVENT_DATA);
}

void vmx_cancel_injection(struct kvm_vcpu *vcpu)
@@ -7347,7 +7356,8 @@ void vmx_cancel_injection(struct kvm_vcpu *vcpu)
__vmx_complete_interrupts(vcpu,
vmcs_read32(VM_ENTRY_INTR_INFO_FIELD),
VM_ENTRY_INSTRUCTION_LEN,
- VM_ENTRY_EXCEPTION_ERROR_CODE);
+ VM_ENTRY_EXCEPTION_ERROR_CODE,
+ INJECTED_EVENT_DATA);

vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);
}
@@ -7501,6 +7511,10 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,

vmx_disable_fb_clear(vmx);

+ /*
+ * Note, even though FRED delivers the faulting linear address via the
+ * event data field on the stack, CR2 is still updated.
+ */
if (vcpu->arch.cr2 != native_read_cr2())
native_write_cr2(vcpu->arch.cr2);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 80c490e71853..8a01225ea8a6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -815,9 +815,22 @@ void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu,
* breakpoint), it is reserved and must be zero in DR6.
*/
vcpu->arch.dr6 &= ~BIT(12);
+
+ /*
+ * FRED #DB event data matches DR6, but follows the polarity of
+ * VMX's pending debug exceptions, not DR6.
+ */
+ ex->event_data = ex->payload & ~BIT(12);
+ break;
+ case NM_VECTOR:
+ ex->event_data = ex->payload;
break;
case PF_VECTOR:
vcpu->arch.cr2 = ex->payload;
+ ex->event_data = ex->payload;
+ break;
+ default:
+ ex->event_data = 0;
break;
}

@@ -925,7 +938,7 @@ static void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,
}

void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned int nr,
- bool has_error_code, u32 error_code)
+ bool has_error_code, u32 error_code, u64 event_data)
{

/*
@@ -950,6 +963,7 @@ void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned int nr,
vcpu->arch.exception.error_code = error_code;
vcpu->arch.exception.has_payload = false;
vcpu->arch.exception.payload = 0;
+ vcpu->arch.exception.event_data = event_data;
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_requeue_exception);

--
2.51.0