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    SubjectRe: [PATCH v2 4/7] export paravirtual cpuid flags in KVM_GET_SUPPORTED_CPUID
    On 05/03/2010 06:52 PM, Glauber Costa wrote:
    > 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/include/asm/kvm_para.h | 4 ++++
    > arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++++++
    > 2 files changed, 31 insertions(+), 0 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    > index 9734808..f019f8c 100644
    > --- a/arch/x86/include/asm/kvm_para.h
    > +++ b/arch/x86/include/asm/kvm_para.h
    > @@ -16,6 +16,10 @@
    > #define KVM_FEATURE_CLOCKSOURCE 0
    > #define KVM_FEATURE_NOP_IO_DELAY 1
    > #define KVM_FEATURE_MMU_OP 2
    > +/* This indicates that the new set of kvmclock msrs
    > + * are available. The use of 0x11 and 0x12 is deprecated
    > + */
    > +#define KVM_FEATURE_CLOCKSOURCE2 3
    >

    Separate patch.

    >
    > #define MSR_KVM_WALL_CLOCK 0x11
    > #define MSR_KVM_SYSTEM_TIME 0x12
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index eb84947..8a7cdda 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -1971,6 +1971,20 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
    > }
    > break;
    > }
    > + case 0x40000000: {
    >

    Use symbolic name, please.

    > + char signature[] = "KVMKVMKVM";
    > + u32 *sigptr = (u32 *)signature;
    > + entry->eax = 1;
    >

    Where did this come from?

    > + entry->ebx = sigptr[0];
    > + entry->ecx = sigptr[1];
    > + entry->edx = sigptr[2];
    >

    Overflow, you're reading 12 bytes from a 10-byte variable.

    > + break;
    > + }
    > + case 0x40000001:
    > + entry->eax = (1<< KVM_FEATURE_CLOCKSOURCE) |
    > + (1<< KVM_FEATURE_NOP_IO_DELAY) |
    > + (1<< KVM_FEATURE_CLOCKSOURCE2);
    >

    Indentation...

    Also, have to initialize all fields, since the real cpu won't initialize
    them for you.

    Sidenote: the real cpu may be a kvm vcpu, so it may in fact support
    those features.

    > + break;
    > case 0x80000000:
    > entry->eax = min(entry->eax, 0x8000001a);
    > break;
    > @@ -2017,6 +2031,19 @@ 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], 0x40000000, 0,&nent, cpuid->nent);
    > + limit = cpuid_entries[nent - 1].eax;
    >

    The kvm cpuid does not follow the limit thing.

    > + for (func = 0x40000001; func<= limit&& nent< cpuid->nent; ++func)
    > + do_cpuid_ent(&cpuid_entries[nent], func, 0,
    > + &nent, cpuid->nent);
    > +
    > r = -E2BIG;
    >

    To avoid confusion, please write Documentation/kvm/cpuid.txt based on
    the current qemu-kvm code, and implement this patch according to the
    documentation.

    --
    error compiling committee.c: too many arguments to function



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