[PATCH v3 2/3] KVM: x86: On emulation failure, convey the exit reason, etc. to userspace
From: David Edmondson
Date: Thu Jul 29 2021 - 09:46:16 EST
Should instruction emulation fail, include the VM exit reason, etc. in
the emulation_failure data passed to userspace, in order that the VMM
can report it as a debugging aid when describing the failure.
Suggested-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
Signed-off-by: David Edmondson <david.edmondson@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 5 ++++
arch/x86/kvm/vmx/vmx.c | 5 +---
arch/x86/kvm/x86.c | 53 ++++++++++++++++++++++++++-------
include/uapi/linux/kvm.h | 7 +++++
4 files changed, 56 insertions(+), 14 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index dfb902930cdc..17da43c1aa67 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1630,6 +1630,11 @@ extern u64 kvm_mce_cap_supported;
int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
void *insn, int insn_len);
+void kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu,
+ bool instruction_bytes,
+ void *data, unsigned int ndata);
+void kvm_prepare_emulation_failure_exit_with_reason(struct kvm_vcpu *vcpu,
+ bool instruction_bytes);
void kvm_enable_efer_bits(u64);
bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fefdecb0ff3d..a8d303c7c099 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5367,10 +5367,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
if (vmx->emulation_required && !vmx->rmode.vm86_active &&
vcpu->arch.exception.pending) {
- vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
- vcpu->run->internal.suberror =
- KVM_INTERNAL_ERROR_EMULATION;
- vcpu->run->internal.ndata = 0;
+ kvm_prepare_emulation_failure_exit_with_reason(vcpu, false);
return 0;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a4fd10604f72..a97bacd8922f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7456,7 +7456,9 @@ void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip)
}
EXPORT_SYMBOL_GPL(kvm_inject_realmode_interrupt);
-static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
+void kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu,
+ bool instruction_bytes,
+ void *data, unsigned int ndata)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
u32 insn_size = ctxt->fetch.end - ctxt->fetch.data;
@@ -7464,10 +7466,10 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION;
- run->emulation_failure.ndata = 0;
+ run->emulation_failure.ndata = 1; /* Always include the flags. */
run->emulation_failure.flags = 0;
- if (insn_size) {
+ if (instruction_bytes && insn_size) {
run->emulation_failure.ndata = 3;
run->emulation_failure.flags |=
KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES;
@@ -7477,7 +7479,42 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
memcpy(run->emulation_failure.insn_bytes,
ctxt->fetch.data, insn_size);
}
+
+ ndata = min((size_t)ndata, sizeof(run->internal.data) -
+ run->emulation_failure.ndata * sizeof(u64));
+ if (ndata) {
+ unsigned int offset =
+ offsetof(struct kvm_run, emulation_failure.flags) +
+ run->emulation_failure.ndata * sizeof(u64);
+
+ memcpy((void *)run + offset, data, ndata);
+ run->emulation_failure.ndata += ndata / sizeof(u64);
+ }
+}
+EXPORT_SYMBOL_GPL(kvm_prepare_emulation_failure_exit);
+
+void kvm_prepare_emulation_failure_exit_with_reason(struct kvm_vcpu *vcpu,
+ bool instruction_bytes)
+{
+ struct {
+ __u64 exit_reason;
+ __u64 exit_info1;
+ __u64 exit_info2;
+ __u32 intr_info;
+ __u32 error_code;
+ } exit_reason;
+
+ static_call(kvm_x86_get_exit_info)(vcpu,
+ &exit_reason.exit_reason,
+ &exit_reason.exit_info1,
+ &exit_reason.exit_info2,
+ &exit_reason.intr_info,
+ &exit_reason.error_code);
+
+ kvm_prepare_emulation_failure_exit(vcpu, instruction_bytes,
+ &exit_reason, sizeof(exit_reason));
}
+EXPORT_SYMBOL_GPL(kvm_prepare_emulation_failure_exit_with_reason);
static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
{
@@ -7493,16 +7530,14 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
if (kvm->arch.exit_on_emulation_error ||
(emulation_type & EMULTYPE_SKIP)) {
- prepare_emulation_failure_exit(vcpu);
+ kvm_prepare_emulation_failure_exit_with_reason(vcpu, true);
return 0;
}
kvm_queue_exception(vcpu, UD_VECTOR);
if (!is_guest_mode(vcpu) && static_call(kvm_x86_get_cpl)(vcpu) == 0) {
- vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
- vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
- vcpu->run->internal.ndata = 0;
+ kvm_prepare_emulation_failure_exit_with_reason(vcpu, false);
return 0;
}
@@ -12095,9 +12130,7 @@ int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
* doesn't seem to be a real use-case behind such requests, just return
* KVM_EXIT_INTERNAL_ERROR for now.
*/
- vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
- vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
- vcpu->run->internal.ndata = 0;
+ kvm_prepare_emulation_failure_exit_with_reason(vcpu, false);
return 0;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d9e4aabcb31a..f1ef4117b824 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -397,6 +397,12 @@ struct kvm_run {
* "ndata" is correct, that new fields are enumerated in "flags",
* and that each flag enumerates fields that are 64-bit aligned
* and sized (so that ndata+internal.data[] is valid/accurate).
+ *
+ * Space beyond the defined fields may be used to
+ * store arbitrary debug information relating to the
+ * emulation failure. It is accounted for in "ndata"
+ * but otherwise unspecified and is not represented in
+ * "flags".
*/
struct {
__u32 suberror;
@@ -404,6 +410,7 @@ struct kvm_run {
__u64 flags;
__u8 insn_size;
__u8 insn_bytes[15];
+ /* Arbitrary debug data may follow. */
} emulation_failure;
/* KVM_EXIT_OSI */
struct {
--
2.30.2