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    SubjectRe: [patch 08/41] x86/fpu: Restrict fpstate sanitizing to legacy components
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    On Fri, Jun 11 2021 at 12:18, Andy Lutomirski wrote:
    > On 6/11/21 12:03 PM, Andy Lutomirski wrote:
    >> On 6/11/21 9:15 AM, Thomas Gleixner wrote:
    >> Does this result in the mxcsr_mask and mxcsr fields being correct?
    >> There is a silly number of special cases there.

    Let me stare at that.

    > The SDM says, in a footnote in XRSTOR:
    >
    > There is an exception if RFBM[1] = 0 and RFBM[2] = 1. In this case, the
    > standard form of XRSTOR will load MXCSR from memory, even though MXCSR
    > is part of state component 1 — SSE. The compacted form of XRSTOR does
    > not make this exception.
    >
    > which makes me think that this code has a bug. Also, the code is
    > manifest nonsense for a different reason:
    >
    > if (!FP)
    > memset(the whole damn thing, 0);
    >
    > if (!SSE)
    > memset(just part of it, 0);
    >
    > which means that, if the FP bit is clear but the SSE bit is set, this
    > thing will clobber the SSE state.
    >
    > This code is garbage. So is the architecture that gave rise to this code.

    No argument about that :)

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