Re: [Qemu-devel] [QEMU 1.2 PATCH] i386: kvm: have a predefined set of default KVM feature bits

[Michael S. Tsirkin]

On Wed, Aug 29, 2012 at 12:04:25PM -0300, Eduardo Habkost wrote:
> We can't simply expose the GET_SUPPORTED_CPUID results directly to the
> guest, or the resulting guest-visible CPUID bits may change under the
> guest's feet when we live-migrate.
> 
> We still have to implement proper per-machine-type migration
> compatibility bits, but this at least is a workaround for cases where PV
> EOI would be silently enabled after a host kernel upgrade.
> 
> We also have to implement proper check/warnings about unsupported bits
> when using "-cpu check" or "-cpu enforce", because the default bits may
> be silently disabled if the host kernel doesn't support them.
> 
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
>  target-i386/cpu.c | 18 +++++++++++++++++-
>  target-i386/cpu.h | 10 ++++++++++
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 120a2e3..52042f0 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -283,6 +283,21 @@ typedef struct x86_def_t {
>            CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A)
>  #define TCG_SVM_FEATURES 0
>  
> +
> +/* List of KVM features we (try to) enable by default
> + * 
> + * CPUID_KVM_PV_EOI is not enabled until we have proper per-machine-type
> + * migration compatibility support
> + * 
> + * CPUID_KVM_MMU is not enabled because it is deprecated.
> + */
> +#define DEFAULT_KVM_FEATURES (CPUID_KVM_CLOCKSOURCE | \
> +                              CPUID_KVM_KVM_NOP_IO_DELAY | \
> +                              CPUID_KVM_CLOCKSOURCE2 | \
> +                              CPUID_KVM_KVM_ASYNC_PF | \
> +                              CPUID_KVM_STEAL_TIME | \
> +                              CPUID_KVM_CLOCKSOURCE_STABLE_BIT)
> +
>  /* maintains list of cpu model definitions
>   */
>  static x86_def_t *x86_defs = {NULL};
> @@ -887,7 +902,8 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, 
> const char *cpu_model)
>          memcpy(x86_cpu_def, def, sizeof(*def));
>      }
>  
> -    plus_kvm_features = ~0; /* not supported bits will be filtered out later 
> */
> +    /* not supported bits will be filtered out later */
> +    plus_kvm_features = DEFAULT_KVM_FEATURES;
>  
>      add_flagname_to_bitmaps("hypervisor", &plus_features,
>          &plus_ext_features, &plus_ext2_features, &plus_ext3_features,
> diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> index 60f9e97..5ce4baf 100644
> --- a/target-i386/cpu.h
> +++ b/target-i386/cpu.h
> @@ -440,6 +440,16 @@
>  #define CPUID_SVM_PAUSEFILTER  (1 << 10)
>  #define CPUID_SVM_PFTHRESHOLD  (1 << 12)
>  
> +/* CPUID[4000_0001h].EAX bits: */
> +#define CPUID_KVM_CLOCKSOURCE             (1 << 0)
> +#define CPUID_KVM_KVM_NOP_IO_DELAY        (1 << 1)
> +#define CPUID_KVM_MMU                     (1 << 2)
> +#define CPUID_KVM_CLOCKSOURCE2            (1 << 3)
> +#define CPUID_KVM_KVM_ASYNC_PF            (1 << 4)
> +#define CPUID_KVM_STEAL_TIME              (1 << 5)
> +#define CPUID_KVM_KVM_PV_EOI              (1 << 6)
> +#define CPUID_KVM_CLOCKSOURCE_STABLE_BIT  (1 << 24)
> +
>  #define CPUID_VENDOR_INTEL_1 0x756e6547 /* "Genu" */
>  #define CPUID_VENDOR_INTEL_2 0x49656e69 /* "ineI" */
>  #define CPUID_VENDOR_INTEL_3 0x6c65746e /* "ntel" */

Why duplicate macros that kvm linux header already has?

> -- 
> 1.7.11.4