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    SubjectRe: [PATCH v4 16/22] x86/fpu/xstate: Extend the table to map state components with features
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    On Sun, Feb 21 2021 at 10:56, Chang S. Bae wrote:
    > +struct xfeature_capflag_info {
    > + int xfeature_idx;
    > + short cpu_cap;

    First of all please format the struct members tabular as x86 does all
    over the place.

    What's the purpose of 'int' 'short' here? This data is unsinged. We have
    no negative feature bits and no negative xfeatures.

    Also if your intention is to save space, then you might want to look at
    the compiler output. It's not saving anything, it's still 8 byte because
    the compiler pads the struct.

    > +};
    > +
    > +static struct xfeature_capflag_info xfeature_capflags[] __initdata = {
    > + { XFEATURE_FP, X86_FEATURE_FPU },
    > + { XFEATURE_SSE, X86_FEATURE_XMM },
    > + { XFEATURE_YMM, X86_FEATURE_AVX },
    > + { XFEATURE_BNDREGS, X86_FEATURE_MPX },
    > + { XFEATURE_BNDCSR, X86_FEATURE_MPX },
    > + { XFEATURE_OPMASK, X86_FEATURE_AVX512F },
    > + { XFEATURE_ZMM_Hi256, X86_FEATURE_AVX512F },
    > + { XFEATURE_Hi16_ZMM, X86_FEATURE_AVX512F },
    > + { XFEATURE_PT_UNIMPLEMENTED_SO_FAR, X86_FEATURE_INTEL_PT },
    > + { XFEATURE_PKRU, X86_FEATURE_PKU },
    > + { XFEATURE_PASID, X86_FEATURE_ENQCMD },
    > };

    And you could have changed the existing table just so:

    static unsigned short xsave_cpuid_features[] __initdata = {
    [XFEATURE_FP] = X86_FEATURE_FPU,
    [XFEATURE_SSE] = X86_FEATURE_XMM,
    [XFEATURE_YMM] = X86_FEATURE_AVX,
    [XFEATURE_BNDREGS] = X86_FEATURE_MPX,
    [XFEATURE_BNDCSR] = X86_FEATURE_MPX,
    [XFEATURE_OPMASK] = X86_FEATURE_AVX512F,
    [XFEATURE_ZMM_Hi256] = X86_FEATURE_AVX512F,
    [XFEATURE_Hi16_ZMM] = X86_FEATURE_AVX512F,
    [XFEATURE_PT_UNIMPLEMENTED_SO_FAR] = X86_FEATURE_INTEL_PT,
    [XFEATURE_PKRU] = X86_FEATURE_PKU,
    [XFEATURE_PASID] = X86_FEATURE_ENQCMD,
    };

    and the implementation to:

    for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
    - if (xsave_cpuid_features[i] || !boot_cpu_has(xsave_cpuid_features[i]))
    + if (xsave_cpuid_features[i] || !boot_cpu_has(xsave_cpuid_features[i]))
    xfeatures_mask_all &= ~BIT_ULL(i);

    Even with the gaps for XTILE the table is smaller, the code is simpler...

    > + for (i = 0; i < ARRAY_SIZE(xfeature_capflags); i++) {
    > + short cpu_cap = xfeature_capflags[i].cpu_cap;
    > + int idx = xfeature_capflags[i].xfeature_idx;
    > +
    > + if (!boot_cpu_has(cpu_cap))
    > + xfeatures_mask_all &= ~BIT_ULL(idx);
    > }
    >
    > xfeatures_mask_all &= fpu__get_supported_xfeatures_mask();

    Thanks,

    tglx

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