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SubjectRe: [PATCH] Pentium Pro - sysenter - doublefault
On Mon, 2003-08-25 at 02:29, Jamie Lokier wrote:
> Jamie Lokier wrote:
> > So that means the sysenter instruction _does_ exist on the PPro and
> > early Pentium II, but it isn't usable.
> If anyone has information on what the SYSENTER and SYSEXIT
> instructions actually do on Intel Pentium Pro or stepping<3 Pentium II
> processors, I am very interested.
> I'm intrigued to know if the buggy behaviour of these instructions is
> really unsafe, or simply hard to use so Intel changed the behaviour.
> (An example of hard to use would be SYSENTER not disabling
> interrupts). If they are safe but hard to use, perhaps the ingenuity
> of kernel hackers can work around the hardness >:)

Hi Jamie,

I tried your test on my machine. It fails with a segmentation
fault. I noticed that the Pentium II specifications update manual
starts with rev C0 stepping (ignoring mask rev < 3).
I'm inclined to forgive Intel for not publishing the scary errata that
goes with the first few mask revs, particularly for an old product.

When I was chasing the original problem, I added tracing code
(compiling the kernel with finstrument-functions) so that when I
got into kgdb after the double-fault I could see that it had just
completed a umask system call. I'm assuming that it failed on
the sysexit.

I keep the old Pentium Pro around because it has an NMI interrupt

I'm happy that Linus has merged the fix to disable correctly
disable sysenter for these machines.

Jim Houston - Concurrent Computer Corp

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