Re: [Xen-devel] [PATCH, fixed] linux/x86: use sysenter/syscall for 32-bit apps on 64-bit Xen

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>However, in case (2) the i386 guest kernel unconditionally goes for
>sysenter, and the hypervisor will accept this because CPUID has advertised
>SEP. *But* AMD CPUs do not support sysenter except in legacy mode! The
>correct thing to do is to use syscall. The hypervisor 32-on-64 compat code
>would accept CALLBACKTYPE_syscall, but the Linux i386 code here doesn't
>appear to make use of it. So I would imagine that the i386 kernel running on
>AMD hardware would cause all user processes to crash when they SYSENTER.

I intentionally avoided adding syscall stuff to the 32-bit kernel, since that 
isn't
there in the native kernel either (as it's not really usable on native). 
Therefore
I'd suggest clearing SEP for pv32-on-64 guests in emulate_forced_invalid_op().

Jan


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