Hi, > On 23 Aug 2021, at 14:22, Julien Grall <[email protected]> wrote: > > > > On 23/08/2021 13:39, Bertrand Marquis wrote: >> Hi Julien, > > Hi Bertrand, > >>> On 23 Aug 2021, at 12:47, Julien Grall <[email protected]> wrote: >>> >>> Hi Bertrand, >>> >>> On 23/08/2021 11:32, Bertrand Marquis wrote: >>>> Replace the code in p2m trying to find a sane value for the VMID size >>>> supported and the PAR to use. We are now using the boot cpuinfo as the >>>> values there are sanitized during boot and the value for those >>>> parameters is now the safest possible value on the system. >>>> On arm32, the system will panic if there are different types of core so >>>> those checks were not needed anyway. >>> >>> So the assumption is that if you have the same MIDR, then you must have the >>> same features. I understand this is what Xen assumes today but I never >>> viewed that check as the truth. It is more to limit the damage on most >>> platform. >> This was the assumption before, I did not change anything but just explained >> in the commit message why this was not possible to come to this code. > > Yes. This is not a new, however I thought I would mention it because I want > to avoid continuing to use wrong assumptions. > > However, this code is arm64 only as it is #ifdef right? (Sorry I should have > looked at the code the first time) So ... > >>> >>> So can you confirm whether this is something that Arm guarantees? >> For a specific MIDR from Arm (ie a Cortex) the PAR is fixed and VMID size to. >> But for an other Arm architecture processor I cannot say. >>> >>> That said, I am not against removing the code. But I would like the comment >>> to be amended if this is not a correct assumption. >> Would the following be acceptable: >> On arm32, Xen is not booting on systems having different MIDR amongst cores >> and it is assumed that cores with the same MIDR will have the same PAR and >> VMID size. > ... I would just drop any mention of arm32 here.
Ok Cheers Bertrand > > Cheers, > > -- > Julien Grall
