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Groups > linux.kernel > #1256860 > unrolled thread
| Started by | Will Deacon <will.deacon@arm.com> |
|---|---|
| First post | 2015-10-27 16:50 +0100 |
| Last post | 2015-10-28 17:20 +0100 |
| Articles | 2 — 1 participant |
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Re: [PATCH] ARM: SWP emulation: Restore original *data when failed Will Deacon <will.deacon@arm.com> - 2015-10-27 16:50 +0100
Re: [PATCH] ARM: SWP emulation: Restore original *data when failed Will Deacon <will.deacon@arm.com> - 2015-10-28 17:20 +0100
| From | Will Deacon <will.deacon@arm.com> |
|---|---|
| Date | 2015-10-27 16:50 +0100 |
| Subject | Re: [PATCH] ARM: SWP emulation: Restore original *data when failed |
| Message-ID | <qoeFA-6WP-5@gated-at.bofh.it> |
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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| From | Will Deacon <will.deacon@arm.com> |
|---|---|
| Date | 2015-10-28 17:20 +0100 |
| Message-ID | <qoBC9-4V4-1@gated-at.bofh.it> |
| In reply to | #1256860 |
On Tue, Oct 27, 2015 at 03:44:24PM +0000, Will Deacon wrote:
> 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.
Right, it passes the simple test case I wrote (which fails under mainline).
Will
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