Re: [Qemu-devel] [PATCH v5 2/3] x86: Data structure changes to support MSR based features

[Eduardo Habkost <ehabkost@redhat.com>]

On Mon, Oct 15, 2018 at 12:47:24PM +0800, Robert Hoo wrote:
> Add FeatureWordType indicator in struct FeatureWordInfo.
> Change feature_word_info[] accordingly.
> Change existing functions that refer to feature_word_info[] accordingly.
> 
> Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> ---
>  target/i386/cpu.c | 188 +++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 136 insertions(+), 52 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index c88876d..d191b9c 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -770,17 +770,36 @@ static void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
>            /* missing:
>            CPUID_XSAVE_XSAVEC, CPUID_XSAVE_XSAVES */
>  
> +typedef enum FeatureWordType {
> +   CPUID_FEATURE_WORD,
> +   MSR_FEATURE_WORD,
> +} FeatureWordType;
> +
>  typedef struct FeatureWordInfo {
> +    FeatureWordType type;
>      /* feature flags names are taken from "Intel Processor Identification and
>       * the CPUID Instruction" and AMD's "CPUID Specification".
>       * In cases of disagreement between feature naming conventions,
>       * aliases may be added.
>       */
>      const char *feat_names[32];
> -    uint32_t cpuid_eax;   /* Input EAX for CPUID */
> -    bool cpuid_needs_ecx; /* CPUID instruction uses ECX as input */
> -    uint32_t cpuid_ecx;   /* Input ECX value for CPUID */
> -    int cpuid_reg;        /* output register (R_* constant) */
> +    union {
> +        /* If type==CPUID_FEATURE_WORD */
> +        struct {
> +            uint32_t eax;   /* Input EAX for CPUID */
> +            bool needs_ecx; /* CPUID instruction uses ECX as input */
> +            uint32_t ecx;   /* Input ECX value for CPUID */
> +            int reg;        /* output register (R_* constant) */
> +        } cpuid;
> +        /* If type==MSR_FEATURE_WORD */
> +        struct {
> +            uint32_t index;
> +            struct {   /*CPUID that enumerate this MSR*/
> +                FeatureWord cpuid_class;
> +                uint32_t    cpuid_flag;
> +            } cpuid_dep;

Aren't you going to use this field anywhere?  Probably we want to
prevent the VM from starting if a bit is set in the feature world
but the cpuid_dep bit is not set.

e.g.:
  qemu-system-x86_64 -cpu Skylake-Client,-arch-capabilities,+rsba
probably should fail to start.

> +        } msr;
> +    };
[...]

-- 
Eduardo