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

#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.

Razvan Cojocaru

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