Messages in this thread Patch in this message | | | Date | Tue, 27 Oct 2015 15:44:24 +0000 | From | Will Deacon <> | Subject | Re: [PATCH] ARM: SWP emulation: Restore original *data when failed |
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On Fri, Oct 16, 2015 at 11:37:29AM +0100, Catalin Marinas wrote: > On Fri, Oct 16, 2015 at 08:52:24AM +0100, Vladimir Murzin wrote: > > > On 15/10/15 14:02, Will Deacon wrote: > > >> diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c > > >> index bcee7abac68e..6039d1eb5912 100644 > > >> --- a/arch/arm64/kernel/armv8_deprecated.c > > >> +++ b/arch/arm64/kernel/armv8_deprecated.c > > >> @@ -284,12 +284,12 @@ static void register_insn_emulation_sysctl(struct ctl_table *table) > > >> __asm__ __volatile__( \ > > >> ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN, \ > > >> CONFIG_ARM64_PAN) \ > > >> - " mov %w2, %w1\n" \ > > >> - "0: ldxr"B" %w1, [%3]\n" \ > > >> - "1: stxr"B" %w0, %w2, [%3]\n" \ > > >> + "0: ldxr"B" %w2, [%3]\n" \ > > >> + "1: stxr"B" %w0, %w1, [%3]\n" \ > > >> " cbz %w0, 2f\n" \ > > >> " mov %w0, %w4\n" \ > > >> "2:\n" \ > > >> + " mov %w1, %w2\n" \ > > >> " .pushsection .fixup,\"ax\"\n" \ > > >> " .align 2\n" \ > > >> "3: mov %w0, %w5\n" \ > > > > On the second thought looks like we still update *data in case stxr > > fails (or I need more coffee). > > I'm on the second cup and I see the same problem. Even if stxr fails, we > fall back through "mov %w1, %w2", so *data is always updated with the > loaded value. Maybe something like below on top of Will's patch:
Yeah, sorry, my original patch was an untested mess. I think we can avoid the "cc" clobber by adding a branch to the slow-path, as below.
Still needs testing, mind.
Will
--->8
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c index 6039d1eb5912..937f5e58a4d3 100644 --- a/arch/arm64/kernel/armv8_deprecated.c +++ b/arch/arm64/kernel/armv8_deprecated.c @@ -288,17 +288,19 @@ static void register_insn_emulation_sysctl(struct ctl_table *table) "1: stxr"B" %w0, %w1, [%3]\n" \ " cbz %w0, 2f\n" \ " mov %w0, %w4\n" \ + " b 3f\n" \ "2:\n" \ " mov %w1, %w2\n" \ + "3:\n" \ " .pushsection .fixup,\"ax\"\n" \ " .align 2\n" \ - "3: mov %w0, %w5\n" \ - " b 2b\n" \ + "4: mov %w0, %w5\n" \ + " b 3b\n" \ " .popsection" \ " .pushsection __ex_table,\"a\"\n" \ " .align 3\n" \ - " .quad 0b, 3b\n" \ - " .quad 1b, 3b\n" \ + " .quad 0b, 4b\n" \ + " .quad 1b, 4b\n" \ " .popsection\n" \ ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN, \ CONFIG_ARM64_PAN) \
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