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

[Robert Hoo <robert.hu@linux.intel.com>]

On Wed, 2018-10-24 at 07:16 -0300, Eduardo Habkost wrote:
> 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.

How about in x86_cpu_filter_features() filters the MSR feature word, if
 its dependent CPUID feature bit is not set?
The filter results will be record in cpu->filtered_features, and print
out, like other filtered features.
> 
> > +        } msr;
> > +    };
> 
> [...]
>