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kvm: x86: Allow userspace to handle emulation errors

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Add a fallback mechanism to the in-kernel instruction emulator that
allows userspace the opportunity to process an instruction the emulator
was unable to.  When the in-kernel instruction emulator fails to process
an instruction it will either inject a #UD into the guest or exit to
userspace with exit reason KVM_INTERNAL_ERROR.  This is because it does
not know how to proceed in an appropriate manner.  This feature lets
userspace get involved to see if it can figure out a better path
forward.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20210510144834.658457-2-aaronlewis@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Aaron Lewis 2021-05-10 07:48:33 -07:00 committed by Paolo Bonzini
parent 27de925044
commit 19238e75bd
4 changed files with 85 additions and 4 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

20
Documentation/virt/kvm/api.rst
View file

@ -6546,6 +6546,7 @@ KVM_RUN_BUS_LOCK flag is used to distinguish between them.
This capability can be used to check / enable 2nd DAWR feature provided
by POWER10 processor.
7.24 KVM_CAP_VM_COPY_ENC_CONTEXT_FROM
-------------------------------------
@ -6603,6 +6604,25 @@ present in the "ibm,hypertas-functions" device-tree property.
This capability is enabled for hypervisors on platforms like POWER9
that support radix MMU.
7.27 KVM_CAP_EXIT_ON_EMULATION_FAILURE
--------------------------------------
:Architectures: x86
:Parameters: args[0] whether the feature should be enabled or not
When this capability is enabled, an emulation failure will result in an exit
to userspace with KVM_INTERNAL_ERROR (except when the emulator was invoked
to handle a VMware backdoor instruction). Furthermore, KVM will now provide up
to 15 instruction bytes for any exit to userspace resulting from an emulation
failure. When these exits to userspace occur use the emulation_failure struct
instead of the internal struct. They both have the same layout, but the
emulation_failure struct matches the content better. It also explicitly
defines the 'flags' field which is used to describe the fields in the struct
that are valid (ie: if KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES is
set in the 'flags' field then both 'insn_size' and 'insn_bytes' have valid data
in them.)
8. Other capabilities.
======================

6
arch/x86/include/asm/kvm_host.h
View file

@ -1114,6 +1114,12 @@ struct kvm_arch {
bool exception_payload_enabled;
bool bus_lock_detection_enabled;
/*
* If exit_on_emulation_error is set, and the in-kernel instruction
* emulator fails to emulate an instruction, allow userspace
* the opportunity to look at it.
*/
bool exit_on_emulation_error;
/* Deflect RDMSR and WRMSR to user space when they trigger a #GP */
u32 user_space_msr_mask;

40
arch/x86/kvm/x86.c
View file

@ -4010,6 +4010,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
#endif
case KVM_CAP_VM_COPY_ENC_CONTEXT_FROM:
case KVM_CAP_SREGS2:
case KVM_CAP_EXIT_ON_EMULATION_FAILURE:
r = 1;
break;
case KVM_CAP_EXIT_HYPERCALL:
@ -5649,6 +5650,13 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.hypercall_exit_enabled = cap->args[0];
r = 0;
break;
case KVM_CAP_EXIT_ON_EMULATION_FAILURE:
r = -EINVAL;
if (cap->args[0] & ~1)
break;
kvm->arch.exit_on_emulation_error = cap->args[0];
r = 0;
break;
default:
r = -EINVAL;
break;
@ -7444,8 +7452,33 @@ 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)
{
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
u32 insn_size = ctxt->fetch.end - ctxt->fetch.data;
struct kvm_run *run = vcpu->run;
run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION;
run->emulation_failure.ndata = 0;
run->emulation_failure.flags = 0;
if (insn_size) {
run->emulation_failure.ndata = 3;
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);
}
}
static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
{
struct kvm *kvm = vcpu->kvm;
++vcpu->stat.insn_emulation_fail;
trace_kvm_emulate_insn_failed(vcpu);
@ -7454,10 +7487,9 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
return 1;
}
if (emulation_type & EMULTYPE_SKIP) {
vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
vcpu->run->internal.ndata = 0;
if (kvm->arch.exit_on_emulation_error ||
(emulation_type & EMULTYPE_SKIP)) {
prepare_emulation_failure_exit(vcpu);
return 0;
}

23
include/uapi/linux/kvm.h
View file

@ -280,6 +280,9 @@ struct kvm_xen_exit {
/* Encounter unexpected vm-exit reason */
#define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4
/* Flags that describe what fields in emulation_failure hold valid data. */
#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0)
/* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
struct kvm_run {
/* in */
@ -383,6 +386,25 @@ struct kvm_run {
__u32 ndata;
__u64 data[16];
} internal;
/*
* KVM_INTERNAL_ERROR_EMULATION
*
* "struct emulation_failure" is an overlay of "struct internal"
* that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of
* KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error
* sub-types, this struct is ABI! It also needs to be backwards
* compatible with "struct internal". Take special care that
* "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).
*/
struct {
__u32 suberror;
__u32 ndata;
__u64 flags;
__u8 insn_size;
__u8 insn_bytes[15];
} emulation_failure;
/* KVM_EXIT_OSI */
struct {
__u64 gprs[32];
@ -1088,6 +1110,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_EXIT_HYPERCALL 201
#define KVM_CAP_PPC_RPT_INVALIDATE 202
#define KVM_CAP_BINARY_STATS_FD 203
#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
#ifdef KVM_CAP_IRQ_ROUTING