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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 24/10/07 15:12, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> 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().

Okay.

 K.



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