Re: [PATCH] Pentium Pro - sysenter - doublefault

[Jamie Lokier]

Pavel Machek wrote:
> > "SEP is unsupported".  It's interesting that Pentium Pro erratum #82
> > is "SYSENTER/SYSEXIT instructions can implicitly load 'null segment
> > selector' to SS and CS registers", implying that SYSENTER does
> > _something_ useful on PPros.
> 
> Well, with CS==0 machine is not going to survive too long.
> If it only happens sometimes you might catch the double fault
> and fixup, but....

The erratum only applies when you load CS==0 _deliberately_, by setting
the MSR to that.

I'm wondering what happens when you don't do silly things - what is
the undocumented behaviour of SYSENTER/SYSEXIT on those chips?

I vaguely recall reading details about the behaviour change made by
Intel, around the time it was done, but I can't see to find it
anywhere.

-- Jamie
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