[PATCH umr] Skip ahead if PDE entry is actually a PTE entry. (v2)

Tom St Denis tom.stdenis at amd.com
Mon Nov 6 18:39:26 UTC 2017

On 06/11/17 01:34 PM, Christian König wrote:
> Am 06.11.2017 um 19:28 schrieb Tom St Denis:
>> On 06/11/17 05:01 AM, Christian König wrote:
>>> Am 04.11.2017 um 18:15 schrieb Tom St Denis:
>>>> Signed-off-by: Tom St Denis <tom.stdenis at amd.com>
>>> Still not perfect, but good enough for now. Patch is Tested-by: 
>>> Christian König <christian.koenig at amd.com>.
>>> I think you need to rework the VM walking a bit, cause we need to 
>>> support the T bit as well in the future and your code make a few 
>>> assumptions which doesn't allow that.
>> Doesn't the T bit imply V=0 which means the page isn't backed by 
>> memory.  Not much umr could do about that other than to print out the 
>> T bit.
> No, the T bit means translate further. In other words it is the counter 
> part of the P bit and means that a PTE should be handled as a PDE.
> But for this to have meaning you also need to handle the fragment size 
> as well (Now I have you totally confused, haven't I? :).

Yes :-)

I thought fragment size was more for hinting to the cache controller and 
not actually part of the VM decoding.

Also the PI docs say T => "Tiled (PRT)" and from what I gather that just 
means the page is valid but might not be backed so instead of raising a 
page fault you raise a new fault that the application (?) handles 

There's an 'F' bit that is labeled "translate further".

Reading section 8 of said document seems to indicate you're confusing 
bits F and T or my doc is wildly out of date (or we're talking about 
different IP revisions)


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