On Wed, Jan 07, 2015 at 11:11:48AM +0000, Will Deacon wrote: > On Wed, Jan 07, 2015 at 10:58:24AM +0000, Leo Yan wrote: > > On Wed, Jan 07, 2015 at 10:10:34AM +0000, Suzuki K. Poulose wrote: > > > On 07/01/15 05:52, Leo Yan wrote: > > > >Currently kernel has set the bit SCTLR_EL1.SED, so the SETEND > > > >instruction will be treated as UNALLOCATED; this error can be > > > >reproduced when ARMv8 cpu runs with EL1/aarch64 and EL0/aarch32 > > > >mode, finally kernel will trap the exception if the userspace > > > >libs use SETEND instruction. > > > > > > > >So this patch clears bit SCTLR_EL1.SED to support SETEND instruction. > > > > > > > The best way to do this, is via the instruction emulation framework > > > added by Punit, which handles the armv8 deprecated/obsoleted > > > instructions. This is now queued for 3.19. > > > I have a patchset which adds the 'SETEND' emulation support to the > > > framework. This will enable better handling of the feature, > > > including finding out the users of the deprecated instruction (when > > > we switch to the emulation mode). > > > > > > > i'm a little confuse for this point: > > > > if the deprecated instructions cannot be supported by CPU, then only > > can use emulation; on the other hand, if CPU can natively support the > > deprecated instruction, why we cannot directly enable this h/w feature? > > if use the emulation mode, suppose here will have performance penalty. > > > > how about u think for this? :-) > > A *huge* advantage of emulation is that we can print a diagnostic to dmesg > warning the user that they are making use of a CPU feature that is likely to > disappear from future revisions of the hardware. We've not been great at > doing this in the past, which led to all the fun around SWP emulation that > you can find in the list archives. > > Furthermore, I think the emulation framework does allow the hardware support > to be enabled, it just doesn't make that the default behaviour. > > In other words; use the emulation to find out where SETEND is being used > and fix those applications wherever you can. In the cases where you're > stuck with a legacy binary, you can enable CPU support if it is available > but that's not a longterm solution. >
Thanks for clarification; Let's use emulation framework as formal method. Thanks, Leo Yan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
