On Wed, Feb 01, 2017 at 06:22:44PM +0000, Catalin Marinas wrote: > On Wed, Feb 01, 2017 at 05:59:48PM +0000, Will Deacon wrote: > > On Wed, Feb 01, 2017 at 05:49:34PM +0000, Catalin Marinas wrote: > > > On Wed, Feb 01, 2017 at 05:41:05PM +0000, Will Deacon wrote: > > > > Maybe > > > > just select ARM64_PAN if the erratum workaround is selected, then > > > > runtime warning if we find that the h/w doesn't have PAN but does have > > > > the erratum (which should never fire)? > > > > > > You still need this workaround even if you don't want any PAN (both sw > > > and hw PAN disabled). I wouldn't want to select ARM64_PAN since it's not > > > a dependency. It's more like if you do need a PAN, make sure you only > > > use the hw one. > > > > True, in the case that all PAN options are disabled we still want this > > to work. How about: > > > > select ARM64_PAN if ARM64_SW_TTBR0_PAN > > As I replied to myself, the above would work for me as well, so let's go > for this. > > > In fact, what's the reason for supporting SW_PAN and ARM64_PAN as a > > config combination? Why not just have "PAN" that enables them both and > > uses the hardware feature if it's there? > > Because SW PAN has a non-trivial performance hit. You would enable SW > PAN only if you are paranoid about security. HW PAN, OTOH, is very cheap > and I wouldn't want to miss enabling it in a single Image supporting > ARMv8.0 and ARMv8.1 just because SW PAN is slow on ARMv8.0. > > IOW, ARM64_PAN is default y while ARM64_SW_TTBR0_PAN is default n.
Ok, in that case, then how about another permutation: we make ARM64_SW_TTBR0_PAN depend on ARM64_PAN? Then when you select "PAN Support" you get a new menu option underneath it for the emulation? I think that solves the erratum case and the use-case above. Will
