Re: [PATCH] xen/arm: p2m: fix pa_range_info for 52-bit pa range

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

On 10/18/22 12:02, Michal Orzel wrote:

Hi Michal,

> Hi Xenia,
>
> On 17/10/2022 19:32, Xenia Ragiadakou wrote:
> > Currently the pa_range_info for the 52-bit pa range advertizes that the
> > p2m root table consists of 8 concatenated tables at level 3, which does
> > not make much sense.
> I think the current code advertises 8 concatenated tables at level -1 (sl0=3 -> 
> root_level=-1)
> which is obviously incorrect, but the commit msg should be updated.
I did the same mistake in my email but I did not want to hijack the 
thread that 's why I did not come back to correct my error.
According to the manual, to support 52-bit pa range with 4KB granule 
with the root table at level -1, you need to set SL2=1 and SL0=0.
SL0=3 configures the root table at level 3.

> Funnily enough p2m_root_level is unsigned so it would lead to overflow
> (p2m_root_level would end up with (1 << 32) - 1 instead of -1).
Actually, currently, there is no support at all in XEN neither for LPA 
(LPA support for 4KB is not checked, VCTR DS and SL2 are not set etc) 
nor level -1 (the root table level is determined only based on sl0, the 
number of possible levels is hardcoded to 4 in many places etc). I don't 
think that there is even support for accessing other than the first 
table of concatenated root tables but I need to verify that (I assume 
this based on the way LPAE_TABLE_INDEX_GS is implemented).
This entry is populated in the pa_range_info table just to prevent XEN 
from falling into this
if ( pa_range >= ARRAY_SIZE(pa_range_info) || 
!pa_range_info[pa_range].pabits )
        panic("Unknown encoding of ID_AA64MMFR0_EL1.PARange %x\n", 
pa_range);
> > In order to support the 52-bit pa size with 4KB granule, the p2m root
> > table needs to be configured either as a single table at level -1 or
> > as 16 concatenated tables at level 0.
> > Since, currently there is not support for level -1, set the
> > root_order and sl0 fields of the corresponding pa_range_info according
> > to the second approach.
> >
> > Signed-off-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>
> ~Michal
--
Xenia