On 18/10/2017 11:26, Paolo Bonzini wrote:
> On 04/10/2017 15:17, Brijesh Singh wrote:
>> + /*
>> + * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
>> + * This can happen if a guest gets a page-fault on data access but the HW
>> + * table walker is not able to read the instruction page (e.g instruction
>> + * page is not present in memory).
>> + *
>> + * Typically, when insn_len is zero, x86_emulate_instruction() walks the
>> + * guest page table and fetches the instruction bytes from guest memory.
>> + * When SEV is enabled, the guest memory is encrypted with guest-specific
>> + * key hence hypervisor will not able to fetch the instruction bytes.
>> + * In those cases we simply restart the guest.
>> + */
>> + if (unlikely(!insn_len) &&
>> + kvm_x86_ops->mem_enc_enabled &&
>> + kvm_x86_ops->mem_enc_enabled(vcpu))
>> + return 1;
>> +
>
> Is it needed to test mem_enc_enabled? Could it instead test for the
> availability of decode assists?
More precisely, you could test "unlikely(insn && !insn_len)" here and,
in svm.c, pass insn as
static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
svm->vmcb->control.insn_bytes : 0
Paolo
