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SubjectRe: [PATCH] Re: UP APIC reenabling vs. cpu type detection o
On Fri, 9 Feb 2001, Petr Vandrovec wrote:

> > Why do you need to mask NMI at all?
> Because of you must provide some function which handles NMI, and as
> you cannot switch IDT and CR3 atomically together, NMI handler has
> to be on same address in both address spaces - at least temporary.

Can't it be?

> And in addition NMI handler in VM would have to switch address spaces
> back, execute NMI handler, and return CPU/MMU back to previous state -
> which may be just in the middle of normal VM<->Linux transition, so
> this context switching cannot use any global variable, it must
> save complete CPU/MMU state on stack. And it must not use any spinlock.

Do you need to pass NMIs to VM at all? NMIs as defined by the PC/AT
architecture are delivered as a result of memory parity errors or ISA
IOCHK errors. Is that functionality really needed in VM?

> If you have any idea how it can be done with NMI unmasked all the way
> around...

It depends on the application -- you may avoid problems by careful coding
and a nested NMI will never happen -- the CPU masks the NMI line
internally, from accepting an NMI till a subsequent iret.

+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+ e-mail:, PGP key available +

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