On Wed, Feb 01, 2017 at 06:34:01PM +0000, Will Deacon wrote: > 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. The problem is that ARM64_PAN is an ARMv8.1 feature and currently grouped accordingly in Kconfig. ARM64_SW_TTBR0_PAN is complementary (and even not recommended on ARMv8.1). We can do this if we break the ARMv8.x feature grouping but just for this erratum, I don't think it's worth. -- Catalin
