Re: [Xen-devel] [PATCH V2] mem_event: Allow emulating an instruction that caused a page fault

[Razvan Cojocaru <rzvncj@xxxxxxxxx>]

> #DF (-1, +12 = 55).  Now that's a pretty unlikely scenario (and I may
> have got some of the details wrong) but the upshot is: a single x86
> instruction can access enormous amounts of memory, so turning off
> protection and single-stepping, especially if you don't trust the OS, is
> exposing a lot more than the single frame you took the first fault on.
Thank you, Tim, for clearing that up. Now, 'touching' a page is quite 
different from 'writing to' a page, and I'm really only interested in 
the latter. So, in a scenario where reads are permitted by default and 
we're only interested in writes, are we still talking about these 
limitations? A MOVSW, for example, only needs to write to a single page, 
even though it does touch more pages in read mode.
Thanks,
Razvan Cojocaru

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