Messages in this thread | | | Date | Tue, 20 May 2008 12:01:23 +0200 | From | Andi Kleen <> | Subject | Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions |
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Suresh Siddha wrote: > On Mon, May 19, 2008 at 04:52:01PM +0200, Mikael Pettersson wrote: >>> But we can >>> use some what similar magic, if the fxsave/fxrstor give away >>> some of the fields at the end of fxsave image (today it is reserved >>> and ignored during fxsave/fxrstor) for software use. >>> We can then use these fields at the end of fpstate, to indicate the presence of >>> xstate. But this requires some architecture changes like giving >>> away this space for SW use. We can take this to architects and >>> see what they think. >> If the HW doesn't store anything valuable there, we could store >> SW flags/cookies there on signal delivery, and clear them before >> fxrstor (unless the HW is known to ignore those fields). >> But it depends on how forgiving the HW is. > > Ok. CPU folks are planning to make some of the bytes at the end of fxsave > image, SW usable.
Are they always zeroed in earlier CPUs though? If not that wouldn't work 100% reliably because whatever cookie you put in could have been there before by chance.
I don't see anything in the SDM guaranteeing zeroing.
-Andi
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