RE: [Xen-devel] [PATCH] small adjustment to asm constraints forc/s19400

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> "Tian, Kevin" <kevin.tian@xxxxxxxxx> 31.03.09 11:47 >>>
>Well, got your point. Those three SYSENTER MSRs are lost after resume.
>We'll verify whether this is the only missing parts.  BTW, in our box 32-on
>-32 S3 works fine, does that mean SYSENTER/SYSEXIT not used in pure
>32bit pv environment, since in Xen 32bit path also misses that important
>recovery?

A 32-bit hypervisor does not expose sysenter to the guest (the feature bit
gets cleared) - iirc this is to prevent the guest from thinking that using
sysenter would provide a performance benefit. Hence restoring these MSRs
in that case would only be needed if Xen itself made use of sysenter, which
however it doesn't (except for the now only theoretical case of the
supervisor-mode-kernel feature).

Jan


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