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KVM: x86: On emulation failure, convey the exit reason, etc. to userspace

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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@oracle.com>
Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210920103737.2696756-4-david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Edmondson 2021-09-20 11:37:36 +01:00 committed by Paolo Bonzini
parent 0a62a0319a
commit e615e35589
4 changed files with 69 additions and 18 deletions
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3
arch/x86/include/asm/kvm_host.h
View file

@ -1667,6 +1667,9 @@ 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,
u64 *data, u8 ndata);
void kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu);
void kvm_enable_efer_bits(u64);
bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);

5
arch/x86/kvm/vmx/vmx.c
View file

@ -5408,10 +5408,7 @@ 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);
return 0;
}

73
arch/x86/kvm/x86.c
View file

@ -7664,29 +7664,78 @@ 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, u64 *data,
u8 ndata, u8 *insn_bytes, u8 insn_size)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
u32 insn_size = ctxt->fetch.end - ctxt->fetch.data;
struct kvm_run *run = vcpu->run;
u64 info[5];
u8 info_start;
/*
* Zero the whole array used to retrieve the exit info, as casting to
* u32 for select entries will leave some chunks uninitialized.
*/
memset(&info, 0, sizeof(info));
static_call(kvm_x86_get_exit_info)(vcpu, (u32 *)&info[0], &info[1],
&info[2], (u32 *)&info[3],
(u32 *)&info[4]);
run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION;
run->emulation_failure.ndata = 0;
/*
* There's currently space for 13 entries, but 5 are used for the exit
* reason and info. Restrict to 4 to reduce the maintenance burden
* when expanding kvm_run.emulation_failure in the future.
*/
if (WARN_ON_ONCE(ndata > 4))
ndata = 4;
/* Always include the flags as a 'data' entry. */
info_start = 1;
run->emulation_failure.flags = 0;
if (insn_size) {
run->emulation_failure.ndata = 3;
BUILD_BUG_ON((sizeof(run->emulation_failure.insn_size) +
sizeof(run->emulation_failure.insn_bytes) != 16));
info_start += 2;
run->emulation_failure.flags |=
KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES;
run->emulation_failure.insn_size = insn_size;
memset(run->emulation_failure.insn_bytes, 0x90,
sizeof(run->emulation_failure.insn_bytes));
memcpy(run->emulation_failure.insn_bytes,
ctxt->fetch.data, insn_size);
memcpy(run->emulation_failure.insn_bytes, insn_bytes, insn_size);
}
memcpy(&run->internal.data[info_start], info, sizeof(info));
memcpy(&run->internal.data[info_start + ARRAY_SIZE(info)], data,
ndata * sizeof(data[0]));
run->emulation_failure.ndata = info_start + ARRAY_SIZE(info) + ndata;
}
static void prepare_emulation_ctxt_failure_exit(struct kvm_vcpu *vcpu)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
prepare_emulation_failure_exit(vcpu, NULL, 0, ctxt->fetch.data,
ctxt->fetch.end - ctxt->fetch.data);
}
void __kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu, u64 *data,
u8 ndata)
{
prepare_emulation_failure_exit(vcpu, data, ndata, NULL, 0);
}
EXPORT_SYMBOL_GPL(__kvm_prepare_emulation_failure_exit);
void kvm_prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
{
__kvm_prepare_emulation_failure_exit(vcpu, NULL, 0);
}
EXPORT_SYMBOL_GPL(kvm_prepare_emulation_failure_exit);
static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
{
struct kvm *kvm = vcpu->kvm;
@ -7701,16 +7750,14 @@ 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);
prepare_emulation_ctxt_failure_exit(vcpu);
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_ctxt_failure_exit(vcpu);
return 0;
}
@ -12336,9 +12383,7 @@ 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);
return 0;
}

6
include/uapi/linux/kvm.h
View file

@ -398,6 +398,11 @@ 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 the format is unspecified and is
* not represented in "flags". Any such information is *not* ABI!
*/
struct {
__u32 suberror;
@ -409,6 +414,7 @@ struct kvm_run {
__u8 insn_bytes[15];
};
};
/* Arbitrary debug data may follow. */
} emulation_failure;
/* KVM_EXIT_OSI */
struct {