* Sebastian Reichel <s...@kernel.org> [150405 06:40]: > Hi, > > On Sun, Apr 05, 2015 at 06:13:47AM +0200, Matthijs van Duin wrote: > > On 4 April 2015 at 00:52, Tony Lindgren <t...@atomide.com> wrote: > > > Right, it affects n900 for sure. My point is that it also seems to > > > affect 37xx versions not listed to suffer from this issue. > > > > They shouldn't... erratum 430973 only affected Cortex-A8 r1, and the > > dm37xx should have an r3p2 right? > > > > A word of caution though: at least on the DM814x and AM335x, secure > > ROM sets bit 6 (IBE) in the Auxiliary Control Register, thereby > > enabling BTB invalidate instructions (which normally execute as nops). > > This is presumably a leftover of the erratum 430973 workaround, but it > > means there is a risk of running afoul of erratum 687067 if BTB > > invalidate by MVA instructions are actually used. > > > > I would actually suggest clearing IBE if it set on Cortex-A8 r2 or > > later processors and a secure monitor call is available to do so > > (there is on the DM814x and AM335x, dunno about the 37xx), also for > > performance reasons: BTB invalidates are quite expensive instructions > > (when enabled). > > So if I understand the issue correct, it would be ok to enable the > 430973 workaround in cpu_v7_switch_mm for arm multiplatform kernels > (mcr p15, 0, r2, c7, c5, 6 @ flush BTAC/BTB). On unaffected > Cortex-A8 platforms the IBE bit should be unset (resulting in a nop > instead of the BTB flush).
Well we only want to enable for cortex-a8 revisions affected by 430973, so a custom cpu_v7_switch_mm seems like the way to go there. And then we need checks for clearing IBE for unaffected cortex-a8 revisions. I'll check to today if I have IBE bit set on the systems where I'm seeing issues that should not be affected by 430973. > So assuming, that the same is true for non Cortex-A8 platforms: Can > the workaround simply be enabled by default if CPU_V7 is selected? It should be enabled conditionally. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
