Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Balasubrmanian, Vignesh]

On 5/8/2024 6:32 PM, Thomas Gleixner wrote:
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>
>
> On Tue, May 07 2024 at 15:23, Vignesh Balasubramanian wrote:
> > +struct xfeat_component {
> > +     u32 xfeat_type;
> > +     u32 xfeat_sz;
> > +     u32 xfeat_off;
> > +     u32 xfeat_flags;
> > +} __packed;
> Why repeating xfeat_ for all member names?
>
>      u32       type;
>      u32       size;
>      u32       offset;
>      u32       flags;
>
> is sufficient and obvious, no?
>
> > +enum custom_feature {
> > +     FEATURE_XSAVE_FP = 0,
> > +     FEATURE_XSAVE_SSE = 1,
> > +     FEATURE_XSAVE_YMM = 2,
> > +     FEATURE_XSAVE_BNDREGS = 3,
> > +     FEATURE_XSAVE_BNDCSR = 4,
> > +     FEATURE_XSAVE_OPMASK = 5,
> > +     FEATURE_XSAVE_ZMM_Hi256 = 6,
> > +     FEATURE_XSAVE_Hi16_ZMM = 7,
> > +     FEATURE_XSAVE_PT = 8,
> > +     FEATURE_XSAVE_PKRU = 9,
> > +     FEATURE_XSAVE_PASID = 10,
> > +     FEATURE_XSAVE_CET_USER = 11,
> > +     FEATURE_XSAVE_CET_SHADOW_STACK = 12,
> > +     FEATURE_XSAVE_HDC = 13,
> > +     FEATURE_XSAVE_UINTR = 14,
> > +     FEATURE_XSAVE_LBR = 15,
> > +     FEATURE_XSAVE_HWP = 16,
> > +     FEATURE_XSAVE_XTILE_CFG = 17,
> > +     FEATURE_XSAVE_XTILE_DATA = 18,
> > +     FEATURE_MAX,
> > +     FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
> > +     FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
> > +};
> Why can't this use the existing 'enum xfeature' which is providing
> exactly the same information already?
First version of patch was similar to what you mentioned here and other 
review comments to use existing kernel definitions.
https://lore.kernel.org/linux-mm/20240314112359.50713-1-vigbalas@xxxxxxx/T/

As per the review comment 
https://lore.kernel.org/linux-mm/20240314162954.GAZfMmAnYQoRjRbRzc@fat_crate.local/ 
, modified the patch to be a independent of kernel internal definitions.
Though this enum and below function  "get_sub_leaf" are not useful now,  
it will be required when we extend for a new/different features.

Please let  us know your suggestions.

I will fix all other review comments in my next version.

> > +#ifdef CONFIG_COREDUMP
> > +static int get_sub_leaf(int custom_xfeat)
> > +{
> > +     switch (custom_xfeat) {
> > +     case FEATURE_XSAVE_YMM:                 return XFEATURE_YMM;
> > +     case FEATURE_XSAVE_BNDREGS:             return XFEATURE_BNDREGS;
> > +     case FEATURE_XSAVE_BNDCSR:              return XFEATURE_BNDCSR;
> > +     case FEATURE_XSAVE_OPMASK:              return XFEATURE_OPMASK;
> > +     case FEATURE_XSAVE_ZMM_Hi256:           return XFEATURE_ZMM_Hi256;
> > +     case FEATURE_XSAVE_Hi16_ZMM:            return XFEATURE_Hi16_ZMM;
> > +     case FEATURE_XSAVE_PT:                  return XFEATURE_PT_UNIMPLEMENTED_SO_FAR;
> > +     case FEATURE_XSAVE_PKRU:                return XFEATURE_PKRU;
> > +     case FEATURE_XSAVE_PASID:               return XFEATURE_PASID;
> > +     case FEATURE_XSAVE_CET_USER:            return XFEATURE_CET_USER;
> > +     case FEATURE_XSAVE_CET_SHADOW_STACK:    return XFEATURE_CET_KERNEL_UNUSED;
> > +     case FEATURE_XSAVE_HDC:                 return XFEATURE_RSRVD_COMP_13;
> > +     case FEATURE_XSAVE_UINTR:               return XFEATURE_RSRVD_COMP_14;
> > +     case FEATURE_XSAVE_LBR:                 return XFEATURE_LBR;
> > +     case FEATURE_XSAVE_HWP:                 return XFEATURE_RSRVD_COMP_16;
> > +     case FEATURE_XSAVE_XTILE_CFG:           return XFEATURE_XTILE_CFG;
> > +     case FEATURE_XSAVE_XTILE_DATA:          return XFEATURE_XTILE_DATA;
> > +     default:
> > +             pr_warn_ratelimited("Not a valid XSAVE Feature.");
> > +             return 0;
> > +     }
> > +}
> This function then maps the identical enums one to one. The only actual
> "functionality" is the default case and that's completely pointless.
thanks,
vigneshbalu.