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

[Razvan Cojocaru <rzvncj@xxxxxxxxx>]

> Razvan, have you tried the n2rwx mode? It'll cause an event for the first 
> access to each page. It'll automatically patch the access (hence 2 rwx) to 
> allow execution to continue unhindered.
>
> So user-space doesn't decide anything, but gets informed about everything 
> (within the constraints of mem event, i.e. no foreign mappings, no Xen 
> mappings).
Hello, yes, I did look at that. Unfortunately, my userspace application 
needs to be notified about subsequent writes to the same page, and once 
the page goes to rwx mode there are no further events. So that's not a 
very useful mechanism.
> If you want to know about every write and decide on every write… you can't have 
> your cake and eat it too, right?
Right.

Thanks,
Razvan Cojocaru

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