RE: [PATCH][SVM] remove FFXSR CPUID bit for AMD-V HVM guests

["Jan Beulich" <jbeulich@novell.com>]

>There is no known issue with FFSRX at this time, an alternative (that
>works) is to modify the code in long_mode_do_msr_write() to not gp fault
>on FFSRX bit being set (this was the original failure).  
>
>        if ( msr_content & ~(EFER_FFSRX | EFER_LME | EFER_LMA | EFER_NX
>| EFER_SCE) )
>        {
>            gdprintk(XENLOG_WARNING, "Trying to set reserved bit in "
>                     "EFER: %"PRIx64"\n", msr_content);
>            goto gp_fault;
>        }
>
>The above code also allows windows to continue installation and function
>seemingly properly.

Then I'd favor this change over the posted one.

>So, to answer your Q, there is not a particular known failure case for
>3DNow! Or FFSRX disablement - the issue would be that there has been no
>directed testing effort concerning 3DNow and FFSRX usages in the guest
>to determine if would be any issues per se.  

For FFSRX, I can't see what issues you would expect. For 3dnow, it's as
good (or as bad) as other MMX or XMM stuff trying to access MMIO, I would
guess: if any of this is used anywhere, I guess some updates to emulation
might be needed.

Jan