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    SubjectRe: [PATCH v9 10/26] x86/fpu/xstate: Update the XSTATE buffer address finder to support dynamic states
    On Fri, Jul 30, 2021 at 07:59:41AM -0700, Chang S. Bae wrote:
    > __raw_xsave_addr() returns the requested component's pointer in an XSTATE
    > buffer, by simply looking up the offset table. The offset used to be fixed,
    > but, with dynamic user states, it becomes variable.
    >
    > get_xstate_size() has a routine to find an offset at runtime. Refactor to
    > use it for the address finder.
    >
    > Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
    > Reviewed-by: Len Brown <len.brown@intel.com>
    > Cc: x86@kernel.org
    > Cc: linux-kernel@vger.kernel.org
    > ---
    > Changes from v5:
    > * Updated for future proofed __raw_xsave_addr().
    >
    > Changes from v3:
    > * Added the function description in the kernel-doc style. (Borislav Petkov)
    > * Removed 'no functional change' in the changelog. (Borislav Petkov)
    > ---
    > arch/x86/kernel/fpu/xstate.c | 78 ++++++++++++++++++++++++------------
    > 1 file changed, 53 insertions(+), 25 deletions(-)
    >
    > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
    > index 26f6d5e0f1ed..98ab10e4da3b 100644
    > --- a/arch/x86/kernel/fpu/xstate.c
    > +++ b/arch/x86/kernel/fpu/xstate.c
    > @@ -182,6 +182,38 @@ static bool xfeature_is_supervisor(int xfeature_nr)
    > return ecx & 1;
    > }
    >
    > +/**
    > + * get_xstate_comp_offset - Find the feature's offset in the compacted
    > + * format.
    > + * @mask: This bitmap tells which components reserved in the format.

    There's that "reserved" confusion thing. Rewrite pls.

    > + * @feature_nr: The feature number
    > + *
    > + * Returns: The offset value
    > + */
    > +static unsigned int get_xstate_comp_offset(u64 mask, int feature_nr)
    > +{
    > + u64 xmask = BIT_ULL(feature_nr + 1) - 1;
    > + unsigned int next_offset, offset = 0;
    > + int i;
    > +
    > + if ((xfeatures_mask_all & xmask) == (mask & xmask))
    > + return xstate_comp_offsets[feature_nr];
    > +
    > + /*
    > + * With the given mask, no relevant size is found. Calculate it by
    > + * summing up each state size.
    > + */
    > + for (next_offset = FXSAVE_SIZE + XSAVE_HDR_SIZE, i = FIRST_EXTENDED_XFEATURE;
    > + i <= feature_nr; i++) {
    > + if (!(mask & BIT_ULL(i)))
    > + continue;
    > +
    > + offset = xstate_aligns[i] ? ALIGN(next_offset, 64) : next_offset;
    > + next_offset += xstate_sizes[i];

    Why is this more complex than it has to be?

    IOW, why can't you simply do:

    offset = FXSAVE_SIZE + XSAVE_HDR_SIZE;
    for (i = FIRST_EXTENDED_XFEATURE; i <= feature_nr; i++) {
    if (!(mask & BIT_ULL(i)))
    continue;

    if (xstate_aligns[i])
    offset = ALIGN(offset, 64);

    offset += xstate_sizes[i];
    }
    return offset;

    like it was before?

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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