Re: [Xen-devel] [PATCH v3] x86/traps: Correct pagefault handling issues introduced in c/s d5c251c

[Tim Deegan <tim@xxxxxxx>]

At 16:53 +0000 on 14 Dec (1481734422), Andrew Cooper wrote:
> There are two bugs.
> 
> Firstly, the ASSERT(paging_mode_only_log_dirty(d)) can trip when servicing a
> hypervisor #PF in the context of an HVM guest, e.g. a copy_to_user() failure
> in the shadow pagetable code.
> 
> Secondly, the entry conditions paging_fault() were previously guarded on
> !paging_mode_external(d) which limited entry to PV contexts, but for both
> guest and hypervisor faults.  Switching this to paging_mode_log_dirty() opened
> it up to HVM contexts as well.
> 
> Reinstate the old !paging_mode_external(d) check, as it is actually the
> relevent fact, and extend the comment to explicitly state that hypervisor
> faults should follow this path.
> 
> Inside, we are now guarenteed to be in the context of a PV guest, so can
> safely use the assertion about log dirty.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Tim Deegan <tim@xxxxxxx>

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