Should instruction emulation fail, include the VM exit reason 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 <[email protected]>
Signed-off-by: David Edmondson <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/vmx/vmx.c | 5 +----
arch/x86/kvm/x86.c | 22 +++++++++++++---------
include/uapi/linux/kvm.h | 7 +++++++
4 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0ee580c68839..2e411e26e40e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1630,6 +1630,8 @@ 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 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 d9a4d6cf6406..4fb240204c2c 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(vcpu, false);
return 0;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 17468d983fbd..bf30b445b65d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7452,7 +7452,8 @@ 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)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
u32 insn_size = ctxt->fetch.end - ctxt->fetch.data;
@@ -7463,7 +7464,7 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
run->emulation_failure.ndata = 0;
run->emulation_failure.flags = 0;
- if (insn_size) {
+ if (insn_size && instruction_bytes) {
run->emulation_failure.ndata = 3;
run->emulation_failure.flags |=
KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES;
@@ -7473,7 +7474,14 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
memcpy(run->emulation_failure.insn_bytes,
ctxt->fetch.data, insn_size);
}
+
+ run->emulation_failure.ndata = 4;
+ run->emulation_failure.flags |=
+ KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON;
+ run->emulation_failure.exit_reason =
+ static_call(kvm_x86_get_exit_reason)(vcpu);
}
+EXPORT_SYMBOL_GPL(kvm_prepare_emulation_failure_exit);
static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
{
@@ -7489,16 +7497,14 @@ 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(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(vcpu, false);
return 0;
}
@@ -12092,9 +12098,7 @@ 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(vcpu, false);
return 0;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d9e4aabcb31a..863195371272 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -282,6 +282,7 @@ struct kvm_xen_exit {
/* Flags that describe what fields in emulation_failure hold valid data. */
#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0)
+#define KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON (1ULL << 1)
/* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
struct kvm_run {
@@ -404,6 +405,12 @@ struct kvm_run {
__u64 flags;
__u8 insn_size;
__u8 insn_bytes[15];
+ /*
+ * The "exit reason" extracted from the
+ * VMCS/VMCB that was the cause of attempted
+ * emulation.
+ */
+ __u64 exit_reason;
} emulation_failure;
/* KVM_EXIT_OSI */
struct {
--
2.30.2
On Tue, Jul 06, 2021, David Edmondson wrote:
> Should instruction emulation fail, include the VM exit reason in the
> emulation_failure data passed to userspace, in order that the VMM can
> report it as a debugging aid when describing the failure.
...
> @@ -7473,7 +7474,14 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
> memcpy(run->emulation_failure.insn_bytes,
> ctxt->fetch.data, insn_size);
> }
> +
> + run->emulation_failure.ndata = 4;
> + run->emulation_failure.flags |=
> + KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON;
> + run->emulation_failure.exit_reason =
> + static_call(kvm_x86_get_exit_reason)(vcpu);
> }
...
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index d9e4aabcb31a..863195371272 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -282,6 +282,7 @@ struct kvm_xen_exit {
>
> /* Flags that describe what fields in emulation_failure hold valid data. */
> #define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0)
> +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON (1ULL << 1)
>
> /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
> struct kvm_run {
> @@ -404,6 +405,12 @@ struct kvm_run {
> __u64 flags;
> __u8 insn_size;
> __u8 insn_bytes[15];
> + /*
> + * The "exit reason" extracted from the
> + * VMCS/VMCB that was the cause of attempted
> + * emulation.
> + */
> + __u64 exit_reason;
Rather than providing just the exit reason and adding another kvm_x86_ops hook,
I would prefer to extend kvm_x86_get_exit_info() to also provide the exit reason
and use that. E.g. on VMX, all exceptions funnel through a single exit reason.
Dumping exit_info_{1,2} and error_code in addition to intr_info might not be all
that useful, but I can't see in harm either, and more info is generally a good
thing.
The only other user of kvm_x86_get_exit_info() is for tracepoints, those could
be modified to not pass in the exit reason.
> } emulation_failure;
> /* KVM_EXIT_OSI */
> struct {
> --
> 2.30.2
>
On Friday, 2021-07-09 at 15:47:08 UTC, Sean Christopherson wrote:
> On Tue, Jul 06, 2021, David Edmondson wrote:
>> Should instruction emulation fail, include the VM exit reason in the
>> emulation_failure data passed to userspace, in order that the VMM can
>> report it as a debugging aid when describing the failure.
>
> ...
>
>> @@ -7473,7 +7474,14 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
>> memcpy(run->emulation_failure.insn_bytes,
>> ctxt->fetch.data, insn_size);
>> }
>> +
>> + run->emulation_failure.ndata = 4;
>> + run->emulation_failure.flags |=
>> + KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON;
>> + run->emulation_failure.exit_reason =
>> + static_call(kvm_x86_get_exit_reason)(vcpu);
>> }
>
> ...
>
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index d9e4aabcb31a..863195371272 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -282,6 +282,7 @@ struct kvm_xen_exit {
>>
>> /* Flags that describe what fields in emulation_failure hold valid data. */
>> #define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0)
>> +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON (1ULL << 1)
>>
>> /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
>> struct kvm_run {
>> @@ -404,6 +405,12 @@ struct kvm_run {
>> __u64 flags;
>> __u8 insn_size;
>> __u8 insn_bytes[15];
>> + /*
>> + * The "exit reason" extracted from the
>> + * VMCS/VMCB that was the cause of attempted
>> + * emulation.
>> + */
>> + __u64 exit_reason;
>
> Rather than providing just the exit reason and adding another kvm_x86_ops hook,
> I would prefer to extend kvm_x86_get_exit_info() to also provide the exit reason
> and use that. E.g. on VMX, all exceptions funnel through a single exit reason.
> Dumping exit_info_{1,2} and error_code in addition to intr_info might not be all
> that useful, but I can't see in harm either, and more info is generally a good
> thing.
>
> The only other user of kvm_x86_get_exit_info() is for tracepoints, those could
> be modified to not pass in the exit reason.
Okay.
>> } emulation_failure;
>> /* KVM_EXIT_OSI */
>> struct {
>> --
>> 2.30.2
>>
dme.
--
What did you learn today? I learnt nothing.