Re: [beta patch] SSE copy_page() / clear_page()

From: Manfred Spraul (manfred@colorfullife.com)
Date: Sat Feb 10 2001 - 04:09:41 EST

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    Doug Ledford wrote:
    >
    > > I have this strong suspicion that your kernel will lock up in a bad way
    > > of you have somebody do something like divide by zero without actually
    > > touching a single FP instruction after the divide (so that the error has
    > > happened, but has not yet been raised as an exception).
    >
    > Or much worse, let the kernel mix-and-match SSE and MMX optimized routines
    > without doing full saves of the FPU on SSE routines, which leads to FPU saves
    > in MMX routines with kernel data in the SSE registers, which then shows up
    > when the app touches those SSE registers and you get use space corruption. My
    > code to handle this type of situation was *very* complex, and I don't think I
    > ever got it quite perfectly right without simply imposing a rule that the
    > kernel could never use both SSE and MMX instructions on the same CPU.
    >

    I don't see that problem:
    * sse_{copy,clear}_page() restore the sse registers before returning.
    * the fpu saves into current->thread.i387.f{,x}save never happen from
    interrupts.

    How can kernel sse values end up in user space? I'm sure I overlook
    something, but what? 

    --
	Manfred
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