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    SubjectRe: [RFC PATCH v2 24/32] kvm: x86: prepare for SEV guest management API support
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    On 02/03/2017 16:17, Brijesh Singh wrote:
    > ASID management:
    > - Reserve asid range for SEV guest, SEV asid range is obtained through
    > CPUID Fn8000_001f[ECX]. A non-SEV guest can use any asid outside the SEV
    > asid range.

    How is backwards compatibility handled?

    > - SEV guest must have asid value within asid range obtained through CPUID.
    > - SEV guest must have the same asid for all vcpu's. A TLB flush is required
    > if different vcpu for the same ASID is to be run on the same host CPU.

    [...]

    > +
    > + /* which host cpu was used for running this vcpu */
    > + bool last_cpuid;

    Should be unsigned int.

    >
    > + /* Assign the asid allocated for this SEV guest */
    > + svm->vmcb->control.asid = asid;
    > +
    > + /* Flush guest TLB:
    > + * - when different VMCB for the same ASID is to be run on the
    > + * same host CPU
    > + * or
    > + * - this VMCB was executed on different host cpu in previous VMRUNs.
    > + */
    > + if (sd->sev_vmcbs[asid] != (void *)svm->vmcb ||

    Why the cast?

    > + svm->last_cpuid != cpu)
    > + svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ALL_ASID;

    If there is a match, you don't need to do anything else (neither reset
    the asid, nor mark it as dirty, nor update the fields), so:

    if (sd->sev_vmcbs[asid] == svm->vmcb &&
    svm->last_cpuid == cpu)
    return;

    svm->last_cpuid = cpu;
    sd->sev_vmcbs[asid] = svm->vmcb;
    svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ALL_ASID;
    svm->vmcb->control.asid = asid;
    mark_dirty(svm->vmcb, VMCB_ASID);

    (plus comments ;)).

    Also, why not TLB_CONTROL_FLUSH_ASID if possible?

    > + svm->last_cpuid = cpu;
    > + sd->sev_vmcbs[asid] = (void *)svm->vmcb;
    > +
    > + mark_dirty(svm->vmcb, VMCB_ASID);

    [...]

    >
    > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
    > index fef7d83..9df37a2 100644
    > --- a/include/uapi/linux/kvm.h
    > +++ b/include/uapi/linux/kvm.h
    > @@ -1284,6 +1284,104 @@ struct kvm_s390_ucas_mapping {
    > /* Memory Encryption Commands */
    > #define KVM_MEMORY_ENCRYPT_OP _IOWR(KVMIO, 0xb8, unsigned long)
    >
    > +/* Secure Encrypted Virtualization mode */
    > +enum sev_cmd_id {

    Please add documentation in Documentation/virtual/kvm/memory_encrypt.txt.

    Paolo

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