Re: [Xen-devel] [PATCH V9 4/5] xen/mm: Clean up pfec handling in gva_to_gfn

[Tim Deegan <tim@xxxxxxx>]

At 22:12 +0800 on 03 Feb (1454537524), Huaitong Han wrote:
> From: George Dunlap <george.dunlap@xxxxxxxxxx>
> 
> At the moment, the pfec argument to gva_to_gfn has two functions:
> 
> * To inform guest_walk what kind of access is happenind
> 
> * As a value to pass back into the guest in the event of a fault.
> 
> Unfortunately this is not quite treated consistently: the hvm_fetch_*
> function will "pre-clear" the PFEC_insn_fetch flag before calling
> gva_to_gfn; meaning guest_walk doesn't actually know whether a given
> access is an instruction fetch or not.  This works now, but will cause
> issues when pkeys are introduced, since guest_walk will need to know
> whether an access is an instruction fetch even if it doesn't return
> PFEC_insn_fetch.
> 
> Fix this by making a clean separation for in and out functionalities
> of the pfec argument:
> 
> 1. Always pass in the access type to gva_to_gfn
> 
> 2. Filter out inappropriate access flags before returning from gva_to_gfn.
> 
> (The PFEC_insn_fetch flag should only be passed to the guest if either NX or
> SMEP is enabled.  See Intel 64 Developer's Manual, Volume 3, Chapter Paging,
> PAGE-FAULT EXCEPTIONS)
> 
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> Signed-off-by: Huaitong Han <huaitong.han@xxxxxxxxx>
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Tim Deegan <tim@xxxxxxx>


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