Re: [Xen-devel] [PATCH v2 1/2] arm/mem_access: adjust check_and_get_page to not rely on current

[George Dunlap <dunlapg@xxxxxxxxx>]

On Wed, Dec 14, 2016 at 8:05 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
>>> Note that ARM does not provide any hardware instruction to translate
>>> an IPA (guest physical address) to a PA. So we have a walker there.
>>>
>>> We also a walk for debugging guest page table (though only when it is
>>> using LPAE). I guess it could be re-used in the case where it is not
>>> possible to do it in hardware. Although, it would be rewritten to make
>>> it safe.
>>
>>
>> This sounds like the kind of thing which would be generally useful,
>> although I'd like to understand the problem better before making
>> suggestions.
>
>
> memaccess will restrict permission of certain memory regions in stage-2 page
> table. For the purpose of the example, lets say read-access as been
> restricted.
>
> One of these memory regions may contain the stage-1 page table. Do you agree
> that the guest will not able to read stage-1 page table due the restriction?

But only if the memory is read-protected, right?  If a guest PT
(stage-1) has read permission but not write permission, the hardware
walker should still work, shouldn't it?

 -George

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