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Re: [Xen-devel] [Patch] x86emul: simplify prefix handling for VMFUNC

>>> On 21.09.16 at 00:35, <paul.c.lai@xxxxxxxxx> wrote:
> On Tue, Sep 20, 2016 at 09:50:15AM -0600, Jan Beulich wrote:
>> Paul, there's been no reply to
>> https://lists.xenproject.org/archives/html/xen-devel/2016-09/msg00380.html 
> The refered to patch, commit a1b1572833, adds a check for vmfunc.
> I look a little time to look at the SDM and finally found the reference.
> The vmfunc can be found in Table A-6 "Opcode Extensions for One- and Two-
> byte Opcodes by Group Number" on page A-18 Vol. 2D of the
>  e64-ia-32-architectures-software-developer-manual-325462.pdf.
> The values for vmfunc match the values in the code.
> I also took the liberty of looking at the other existing cases in the
> switch statement, and can find RDTSCP and INVLPG. The CLZERO extension
> value is a mystery to me.

Well - the question raised was whether the documentation is
perhaps wrong. VMFUNC allowing 66, F2, and F3 prefixes when
other opcodes in its neighborhood (e.g. xsetbv, xtest, xend)
don't seems at least suspicious. Extensions originating from AMD
(rdtscp, clzero) can't be reasonably taken for reference.


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