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Subject[PATCH 2/2] KVM: x86: On emulation failure, convey the exit reason to userspace
Date
To aid in debugging.

Suggested-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
arch/x86/kvm/x86.c | 23 +++++++++++++++++------
include/uapi/linux/kvm.h | 2 ++
2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8166ad113fb2..48ef0dc68faf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7455,7 +7455,7 @@ 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)
+static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu, uint64_t flags)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
u32 insn_size = ctxt->fetch.end - ctxt->fetch.data;
@@ -7466,7 +7466,8 @@ 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 &&
+ (flags & KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES)) {
run->emulation_failure.ndata = 3;
run->emulation_failure.flags |=
KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES;
@@ -7476,6 +7477,14 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
memcpy(run->emulation_failure.insn_bytes,
ctxt->fetch.data, insn_size);
}
+
+ if (flags & KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON) {
+ 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);
+ }
}

static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
@@ -7492,16 +7501,18 @@ 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);
+ prepare_emulation_failure_exit(
+ vcpu,
+ KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES |
+ KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON);
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;
+ prepare_emulation_failure_exit(
+ vcpu, KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON);
return 0;
}

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 68c9e6d8bbda..3e4126652a67 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 +405,7 @@ struct kvm_run {
__u64 flags;
__u8 insn_size;
__u8 insn_bytes[15];
+ __u64 exit_reason;
} emulation_failure;
/* KVM_EXIT_OSI */
struct {
--
2.30.2
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