Re: [Xen-devel] [PATCH] x86: machine check exception handling

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 22/6/07 07:57, "Jan Beulich" <jbeulich@xxxxxxxxxx> 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. 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.

 -- Keir



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