Re: [PATCH] deal with interrupt shadow state for emulated instruction

[Avi Kivity <avi@redhat.com>]

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.