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    Subject[PATCH 5/9] export paravirtual cpuid flags in KVM_GET_SUPPORTED_CPUID
    Date
    Right now, we were using individual KVM_CAP entities to communicate
    userspace about which cpuids we support. This is suboptimal, since it
    generates a delay between the feature arriving in the host, and
    being available at the guest.

    A much better mechanism is to list para features in KVM_GET_SUPPORTED_CPUID.
    This makes userspace automatically aware of what we provide. And if we
    ever add a new cpuid bit in the future, we have to do that again,
    which create some complexity and delay in feature adoption.

    Signed-off-by: Glauber Costa <glommer@redhat.com>
    ---
    arch/x86/kvm/x86.c | 34 ++++++++++++++++++++++++++++++++++
    1 files changed, 34 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index eb84947..a51b560 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -1971,6 +1971,23 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
    }
    break;
    }
    + case KVM_CPUID_SIGNATURE: {
    + char signature[12] = "KVMKVMKVM\0\0";
    + u32 *sigptr = (u32 *)signature;
    + entry->eax = 0;
    + entry->ebx = sigptr[0];
    + entry->ecx = sigptr[1];
    + entry->edx = sigptr[2];
    + break;
    + }
    + case KVM_CPUID_FEATURES:
    + entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
    + (1 << KVM_FEATURE_NOP_IO_DELAY) |
    + (1 << KVM_FEATURE_CLOCKSOURCE2);
    + entry->ebx = 0;
    + entry->ecx = 0;
    + entry->edx = 0;
    + break;
    case 0x80000000:
    entry->eax = min(entry->eax, 0x8000001a);
    break;
    @@ -2017,6 +2034,23 @@ static int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
    for (func = 0x80000001; func <= limit && nent < cpuid->nent; ++func)
    do_cpuid_ent(&cpuid_entries[nent], func, 0,
    &nent, cpuid->nent);
    +
    +
    +
    + r = -E2BIG;
    + if (nent >= cpuid->nent)
    + goto out_free;
    +
    + do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_SIGNATURE, 0, &nent,
    + cpuid->nent);
    +
    + r = -E2BIG;
    + if (nent >= cpuid->nent)
    + goto out_free;
    +
    + do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_FEATURES, 0, &nent,
    + cpuid->nent);
    +
    r = -E2BIG;
    if (nent >= cpuid->nent)
    goto out_free;
    --
    1.6.2.2


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