On Thu, 8 Feb 2001, Mikael Pettersson wrote:
> No, poking into MSRs not explicitly defined on the current CPU is
> inherently unsafe. I have several x86 CPU data sheets here in front
> of me which say the same thing: "Don't write to undocumented MSRs."
Your point is right -- the problem are not undefined MSRs (that raise
#GP(0) on an access) but undocumented ones, sigh...
> You cannot assume that every single x86 out there stays clear of
> all Intel-defined MSRs. Intel has also expanded this set over time:
> older designs may not even have known about the APIC_BASE MSR.
Intel is actually sane -- you get #GP(0) for this MSR on P5. Others
might not and there are less cluefull vendors out there.
> 1. identify_cpu() (and more importantly get_cpu_vendor()) is called
[...]
> 2. include/asm-i386/processor.h #defines X86_VENDOR_INTEL as 0.
[...]
> 3. init/main.c calls time_init() before check_bugs() and thus
[...]
> 4. The cpu detection code rewrite in 2.4.0-test<something>
[...]
Yes, there are more problems as well. I'm working on it -- you may want
to look at the preliminary patch I sent here on Monday (strangely enough,
nobody out of linux-kernel seemed to be interested so far). Next version
should be available later this week -- the main problem with moving
identify_cpu() earlier are other cpu_data fields that get initialized
later, so more code needs to be actually rewritten.
> Ideally, identify_cpu() should be run before init_apic_mappings(),
> but my attempts to do so has so far had some weird side-effects
> (lost interrupts, incorrect bogomips, apparently stuck watchdog,
> and keyboard timeouts), so I won't touch that stuff.
You see. I'm going to move identify_cpu() very early anyway, but this
need a careful code review.
Maciej
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: [EMAIL PROTECTED], PGP key available +
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