From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 1 Feb 2017 17:59:48 +0000 Subject: [PATCH v4 2/4] arm64: Work around Falkor erratum 1003 In-Reply-To: <20170201174934.GF26507@e104818-lin.cambridge.arm.com> References: <20170125155232.10277-1-cov@codeaurora.org> <20170125155232.10277-2-cov@codeaurora.org> <20170131123735.GD11191@leverpostej> <36478002-4cd8-7f1c-1a25-8bfe35022a47@codeaurora.org> <3cab36fb-984a-beae-64db-6ce830ba94f6@arm.com> <20170201163358.GG8177@arm.com> <20170201173609.GE26507@e104818-lin.cambridge.arm.com> <20170201174105.GK8177@arm.com> <20170201174934.GF26507@e104818-lin.cambridge.arm.com> Message-ID: <20170201175947.GL8177@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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: > > On Wed, Feb 01, 2017 at 05:36:09PM +0000, Catalin Marinas wrote: > > > On Wed, Feb 01, 2017 at 04:33:58PM +0000, Will Deacon wrote: > > > > On Wed, Feb 01, 2017 at 11:29:22AM -0500, Christopher Covington wrote: > > > > > On 01/31/2017 12:56 PM, Marc Zyngier wrote: > > > > > > Given that all ARMv8 CPUs can support SW_PAN, it is more likely to be > > > > > > enabled than the ARMv8.1 PAN. I'd vote for supporting the workaround in > > > > > > that case too, and hope that people do enable the HW version. > > > > > > > > > > Okay, I'll do my best to add support for the SW PAN case. I rebased and > > > > > submitted v6 of the E1009 patch [1] so that it no longer depends on this > > > > > patch landing first, if you all are inclined to pick it up while work on > > > > > this E1003 patch continues. > > > > > > > > The alternative is not enabling SW_PAN (at runtime) if this errata is > > > > present, along with a warning stating that hardware-PAN should be > > > > enabled in kconfig instead. Not sure what distributions will make of that > > > > though. > > > > > > The problem with this patch is that when ARM64_SW_TTBR0_PAN is enabled > > > and in the absence of hardware PAN (or ARM64_PAN disabled), > > > cpu_do_switch_mm is no longer called for user process switching, so the > > > workaround is pretty much useless. > > > > Oh, I see what you mean now. > > > > > I'm ok with adding the Kconfig dependency below to > > > QCOM_FALKOR_ERRATUM_1003: > > > > > > depends on !ARM64_SW_TTBR0_PAN || ARM64_PAN > > > > > > together with a run-time warning if ARM64_SW_TTBR0_PAN is being used. > > > > That makes it look like hardware-PAN is the cause of the erratum. > > With the right Kconfig comment we could make this clearer. It's not just a comment though, the kconfig option for the workaround will disappear from menuconfig as long as the dependencies aren't met. The dependency is really that SW_PAN depends on !ERRATUM_1003, but that doesn't work for the distributions. > > 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 ? 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? Will