Messages in this thread Patch in this message | | | Date | Wed, 7 Jan 2015 18:58:24 +0800 | From | Leo Yan <> | Subject | Re: [PATCH] arm64: mm: support instruction SETEND |
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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? :-)
> >Signed-off-by: Leo Yan <leo.yan@linaro.org> > >Signed-off-by: Xiaolong Ye <yexl@marvell.com> > >--- > > arch/arm64/mm/proc.S | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > >diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > >index 4e778b1..66a7363 100644 > >--- a/arch/arm64/mm/proc.S > >+++ b/arch/arm64/mm/proc.S > >@@ -249,9 +249,9 @@ ENDPROC(__cpu_setup) > > * CE0 XWHW CZ ME TEEA S > > * .... .IEE .... NEAI TE.I ..AD DEN0 ACAM > > * 0011 0... 1101 ..0. ..0. 10.. .... .... < hardware reserved > >- * .... .1.. .... 01.1 11.1 ..01 0001 1101 < software settings > >+ * .... .1.. .... 01.1 11.1 ..00 0001 1101 < software settings > > */ > > .type crval, #object > > crval: > >- .word 0x000802e2 // clear > >- .word 0x0405d11d // set > >+ .word 0x000803e2 // clear > >+ .word 0x0405d01d // set > > > >
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