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SubjectRe: [PATCH] deal with interrupt shadow state for emulated instruction
H. Peter Anvin wrote:
> Avi Kivity wrote:
>
>> The comment about repeating 'mov ss' in the manual has that wonderful
>> word in it, May. That means we're perfectly allowed to ignore it and
>> just set the flag unconditionally.
>>
>>
>
> Realistically, though, this should only be done for a limited number of
> sequential instructions.
>
>

Why? Do you see a guest filling all of memory with 'mov ss' and
expecting to break out of it via an interrupt?

>> I doubt we'll ever see a repeated 'mov ss', once is more than enough.
>>
>
> True enough, except maliciously.
>

Why do we care? The guest can only harm itself, and if it wants to
disable interrupts, it would be a lot easier for it to run a plain 'cli'.

I guess it would be a problem if we emulated 'mov ss' for ordinary
userspace or vm86 mode, but we don't.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.



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