On 02/01/2017 01:38 PM, Catalin Marinas wrote: > 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.
Thanks all. I've used "select ARM64_PAN if ARM64_SW_TTBR0_PAN" in v6. Thanks, Cov -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
