Commit e615e355 authored by David Edmondson's avatar David Edmondson Committed by Paolo Bonzini
Browse files

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



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: default avatarJoao Martins <joao.m.martins@oracle.com>
Signed-off-by: default avatarDavid Edmondson <david.edmondson@oracle.com>
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210920103737.2696756-4-david.edmondson@oracle.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0a62a031

arch/x86/include/asm/kvm_host.h

+3 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/vmx/vmx.c

+1 −4
Original line number Diff line number Diff line
@@ -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;

		}

arch/x86/kvm/x86.c

+59 −14
Original line number Diff line number Diff line
@@ -7664,28 +7664,77 @@ 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)

{
@@ -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;

}

include/uapi/linux/kvm.h

+6 −0
Original line number Diff line number Diff line
@@ -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 {