Messages in this thread | | | Date | Tue, 14 Apr 2009 19:14:12 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH] deal with interrupt shadow state for emulated instruction |
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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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