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SubjectRe: [Part2 PATCH v5 31/31] KVM: X86: Restart the guest when insn_len is zero and SEV is enabled
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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?

Thanks,

Paolo

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