On Thu, Dec 06, 2018 at 02:35:20PM +0000, Suzuki K Poulose wrote: > > > On 06/12/2018 12:26, Steve Capper wrote: > > On Wed, Dec 05, 2018 at 06:22:27PM +0000, Suzuki K Poulose wrote: > > > Hi Steve, > > > > > [...] > > > I think we may need a check for the secondary CPUs to make sure that they have > > > the 52bit support once the boot CPU has decided to use the feature and fail the > > > CPU bring up (just like we do for the granule support). > > > > > > Suzuki > > > > Hi Suzuki, > > I have just written a patch to detect a mismatch between 52-bit VA that > > is being tested now. > > > > As 52-bit kernel VA support is coming in future, the patch checks for a > > mismatch during the secondary boot path and, if one is found, prevents > > the secondary from booting (and displays an error message to the user). > > Right now, it is the boot CPU which decides the Userspace 52bit VA, isn't it ? > Irrespective of the kernel VA support, the userspace must be able to run on > all the CPUs on the system, right ? So don't we need it now, with this series ? Hi Suzuki, Yes the boot CPU determines vabits_user. My idea was to have the secondary CPUs check to see if vabits_user was 52, and if so, then check to see if it's capable of supporting 52-bit. If not, then it stops booting (and sets a flag to indicate why). This check will be valid for 52-bit userspace support and also valid for 52-bit kernel support (as the check is performed before the secondary mmu is enabled). I didn't want to write a higher level detection routine for the userspace support and then have to re-write it later when introducing 52-bit kernel support. I'm happy to do what works though, I thought this way was simplest :-). Cheers, -- Steve
