Re: [PATCH] x86: machine check exception handling

["Jan Beulich" <jbeulich@novell.com>]

>>> Keir Fraser <Keir.Fraser@cl.cam.ac.uk> 22.06.07 09:15 >>>
>On 22/6/07 07:57, "Jan Beulich" <jbeulich@novell.com> wrote:
>
>>> 3. Most contentious, I'm sure: removed VMX changes that would keep
>>> interrupts disabled across NMI/MCE. The reason is simply that SVM does not
>>> bother with this. If there is a requirement that NMI/MCE be called with
>>> particular constraints on EFLAGS, then we should make that clear and fix up
>>> both VMX and SVM in a separate patch. The pain of this is that it would
>>> probably require extra checks on critical vmexit paths. Is it *really* that
>>> bad for #MC to get interrupted?
>> 
>> Yes, I think it is bad - the machine is known to be a in bad condition
>> already,
>> and by allowing external interrupts you make the situation even worse.
>> Consequently I think SVM should be fixed to only conditionally enable
>> interrupts, just like VMX does.
>
>What issue do you think ExtInts will introduce? A crash before we get a
>fatal error dump onto the Xen console? This argument seems more than a
>little dubious to me.

Why - such a crash would be *very* difficult to debug, as you likely wouldn't
be able to guess the original reason.

> But if we want to complicate the CLI/STI logic of VMX
>and SVM then I think we should do that by pushing STI/CLI (or STGI/CLGI)
>handling into the individual cases of the main demux switch statements in
>vmx.c and svm.c.

Jan