* Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions @ 2013-12-04 1:36 H. Peter Anvin 2013-12-04 8:59 ` Ingo Molnar 2013-12-04 22:51 ` [tip:x86/urgent] x86, bitops: Correct the assembly constraints to testing bitops tip-bot for H. Peter Anvin 0 siblings, 2 replies; 5+ messages in thread From: H. Peter Anvin @ 2013-12-04 1:36 UTC (permalink / raw) To: Peter Zijlstra; +Cc: Ingo Molnar, Jesse Brandeburg, Linux Kernel Mailing List Hi guys, 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions causes a regression, because it incorrectly changed the constraints of bitops. Specifically, the GEN_BINARY_RMWcc() hardcodes a constraint as "er", but it needs to be "Ir" for the bitops themselves. "I" is correct (as opposed to "J" even on 64 bits, because we only generate the 64-bit version when we have a register operand. Unfortunately there isn't a way we can get gcc+gas to generate a version with an offset pointer. -hpa ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions 2013-12-04 1:36 Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions H. Peter Anvin @ 2013-12-04 8:59 ` Ingo Molnar 2013-12-04 16:44 ` H. Peter Anvin 2013-12-04 22:51 ` [tip:x86/urgent] x86, bitops: Correct the assembly constraints to testing bitops tip-bot for H. Peter Anvin 1 sibling, 1 reply; 5+ messages in thread From: Ingo Molnar @ 2013-12-04 8:59 UTC (permalink / raw) To: H. Peter Anvin Cc: Peter Zijlstra, Jesse Brandeburg, Linux Kernel Mailing List * H. Peter Anvin <hpa@zytor.com> wrote: > Hi guys, > > 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() > functions > > causes a regression, because it incorrectly changed the constraints of > bitops. > > Specifically, the GEN_BINARY_RMWcc() hardcodes a constraint as "er", but > it needs to be "Ir" for the bitops themselves. "I" is correct (as > opposed to "J" even on 64 bits, because we only generate the 64-bit > version when we have a register operand. > > Unfortunately there isn't a way we can get gcc+gas to generate a version > with an offset pointer. Does the regression manifest itself in any actual breakage - if yes, how does it look like? (People experiencing similar symptoms will be helped by seeing a fix matching their problems.) Thanks, ngo ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions 2013-12-04 8:59 ` Ingo Molnar @ 2013-12-04 16:44 ` H. Peter Anvin 2014-01-31 21:32 ` Alex Williamson 0 siblings, 1 reply; 5+ messages in thread From: H. Peter Anvin @ 2013-12-04 16:44 UTC (permalink / raw) To: Ingo Molnar; +Cc: Peter Zijlstra, Jesse Brandeburg, Linux Kernel Mailing List On 12/04/2013 12:59 AM, Ingo Molnar wrote: > > * H. Peter Anvin <hpa@zytor.com> wrote: > >> Hi guys, >> >> 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() >> functions >> >> causes a regression, because it incorrectly changed the constraints of >> bitops. >> >> Specifically, the GEN_BINARY_RMWcc() hardcodes a constraint as "er", but >> it needs to be "Ir" for the bitops themselves. "I" is correct (as >> opposed to "J" even on 64 bits, because we only generate the 64-bit >> version when we have a register operand. >> >> Unfortunately there isn't a way we can get gcc+gas to generate a version >> with an offset pointer. > > Does the regression manifest itself in any actual breakage - if yes, > how does it look like? (People experiencing similar symptoms will be > helped by seeing a fix matching their problems.) > It was discovered because it caused a build failure in a not-yet-submitted driver patch. This happens when someone uses test_and_set_bit() or another similar operation on a fixed bit index above 255; the assembler throws an error at that point and the build fails. *HOWEVER*, for bit indicies in the range 32-255, the current code will instead silently miscompile, as the CPU will truncate the argument to 5 bits. I don't know if there are any such instances in the current kernel, but it is entirely possible there is, with unknown but potentially disastrous results. -hpa ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions 2013-12-04 16:44 ` H. Peter Anvin @ 2014-01-31 21:32 ` Alex Williamson 0 siblings, 0 replies; 5+ messages in thread From: Alex Williamson @ 2014-01-31 21:32 UTC (permalink / raw) To: H. Peter Anvin Cc: Ingo Molnar, Peter Zijlstra, Jesse Brandeburg, Linux Kernel Mailing List On Wed, 2013-12-04 at 08:44 -0800, H. Peter Anvin wrote: > On 12/04/2013 12:59 AM, Ingo Molnar wrote: > > > > * H. Peter Anvin <hpa@zytor.com> wrote: > > > >> Hi guys, > >> > >> 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() > >> functions > >> > >> causes a regression, because it incorrectly changed the constraints of > >> bitops. > >> > >> Specifically, the GEN_BINARY_RMWcc() hardcodes a constraint as "er", but > >> it needs to be "Ir" for the bitops themselves. "I" is correct (as > >> opposed to "J" even on 64 bits, because we only generate the 64-bit > >> version when we have a register operand. > >> > >> Unfortunately there isn't a way we can get gcc+gas to generate a version > >> with an offset pointer. > > > > Does the regression manifest itself in any actual breakage - if yes, > > how does it look like? (People experiencing similar symptoms will be > > helped by seeing a fix matching their problems.) > > > > It was discovered because it caused a build failure in a > not-yet-submitted driver patch. This happens when someone uses > test_and_set_bit() or another similar operation on a fixed bit index > above 255; the assembler throws an error at that point and the build fails. > > *HOWEVER*, for bit indicies in the range 32-255, the current code will > instead silently miscompile, as the CPU will truncate the argument to 5 > bits. I don't know if there are any such instances in the current > kernel, but it is entirely possible there is, with unknown but > potentially disastrous results. I'm seeing reports from folks using vfio for PCI device assignment through QEMU that hugepages aren't being released on VM shutdown and reverting 0c44c2d0f459 resolves the problem. I haven't confirmed this myself nor do I pretend to understand the changes this commit makes. Thanks, Alex ^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip:x86/urgent] x86, bitops: Correct the assembly constraints to testing bitops 2013-12-04 1:36 Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions H. Peter Anvin 2013-12-04 8:59 ` Ingo Molnar @ 2013-12-04 22:51 ` tip-bot for H. Peter Anvin 1 sibling, 0 replies; 5+ messages in thread From: tip-bot for H. Peter Anvin @ 2013-12-04 22:51 UTC (permalink / raw) To: linux-tip-commits Cc: linux-kernel, hpa, mingo, peterz, tglx, jesse.brandeburg, hpa Commit-ID: e0f6dec35f9286e78879fe1ac92803fd69fc4fdc Gitweb: http://git.kernel.org/tip/e0f6dec35f9286e78879fe1ac92803fd69fc4fdc Author: H. Peter Anvin <hpa@linux.intel.com> AuthorDate: Wed, 4 Dec 2013 14:31:28 -0800 Committer: H. Peter Anvin <hpa@linux.intel.com> CommitDate: Wed, 4 Dec 2013 14:31:28 -0800 x86, bitops: Correct the assembly constraints to testing bitops In checkin: 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions the various functions which do modify and test were unified and optimized using "asm goto". However, this change missed the detail that the bitops require an "Ir" constraint rather than an "er" constraint ("I" = integer constant from 0-31, "e" = signed 32-bit integer constant). This would cause code to miscompile if these functions were used on constant bit positions 32-255 and the build to fail if used on constant bit positions above 255. Add the constraints as a parameter to the GEN_BINARY_RMWcc() macro to avoid this problem. Reported-by: Jesse Brandeburg <jesse.brandeburg@intel.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/529E8719.4070202@zytor.com --- arch/x86/include/asm/atomic.h | 4 ++-- arch/x86/include/asm/atomic64_64.h | 4 ++-- arch/x86/include/asm/bitops.h | 6 +++--- arch/x86/include/asm/local.h | 4 ++-- arch/x86/include/asm/rmwcc.h | 8 ++++---- 5 files changed, 13 insertions(+), 13 deletions(-) diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h index da31c8b..b17f4f4 100644 --- a/arch/x86/include/asm/atomic.h +++ b/arch/x86/include/asm/atomic.h @@ -77,7 +77,7 @@ static inline void atomic_sub(int i, atomic_t *v) */ static inline int atomic_sub_and_test(int i, atomic_t *v) { - GEN_BINARY_RMWcc(LOCK_PREFIX "subl", v->counter, i, "%0", "e"); + GEN_BINARY_RMWcc(LOCK_PREFIX "subl", v->counter, "er", i, "%0", "e"); } /** @@ -141,7 +141,7 @@ static inline int atomic_inc_and_test(atomic_t *v) */ static inline int atomic_add_negative(int i, atomic_t *v) { - GEN_BINARY_RMWcc(LOCK_PREFIX "addl", v->counter, i, "%0", "s"); + GEN_BINARY_RMWcc(LOCK_PREFIX "addl", v->counter, "er", i, "%0", "s"); } /** diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h index 3f065c9..46e9052 100644 --- a/arch/x86/include/asm/atomic64_64.h +++ b/arch/x86/include/asm/atomic64_64.h @@ -72,7 +72,7 @@ static inline void atomic64_sub(long i, atomic64_t *v) */ static inline int atomic64_sub_and_test(long i, atomic64_t *v) { - GEN_BINARY_RMWcc(LOCK_PREFIX "subq", v->counter, i, "%0", "e"); + GEN_BINARY_RMWcc(LOCK_PREFIX "subq", v->counter, "er", i, "%0", "e"); } /** @@ -138,7 +138,7 @@ static inline int atomic64_inc_and_test(atomic64_t *v) */ static inline int atomic64_add_negative(long i, atomic64_t *v) { - GEN_BINARY_RMWcc(LOCK_PREFIX "addq", v->counter, i, "%0", "s"); + GEN_BINARY_RMWcc(LOCK_PREFIX "addq", v->counter, "er", i, "%0", "s"); } /** diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h index 6d76d09..9fc1af7 100644 --- a/arch/x86/include/asm/bitops.h +++ b/arch/x86/include/asm/bitops.h @@ -205,7 +205,7 @@ static inline void change_bit(long nr, volatile unsigned long *addr) */ static inline int test_and_set_bit(long nr, volatile unsigned long *addr) { - GEN_BINARY_RMWcc(LOCK_PREFIX "bts", *addr, nr, "%0", "c"); + GEN_BINARY_RMWcc(LOCK_PREFIX "bts", *addr, "Ir", nr, "%0", "c"); } /** @@ -251,7 +251,7 @@ static inline int __test_and_set_bit(long nr, volatile unsigned long *addr) */ static inline int test_and_clear_bit(long nr, volatile unsigned long *addr) { - GEN_BINARY_RMWcc(LOCK_PREFIX "btr", *addr, nr, "%0", "c"); + GEN_BINARY_RMWcc(LOCK_PREFIX "btr", *addr, "Ir", nr, "%0", "c"); } /** @@ -304,7 +304,7 @@ static inline int __test_and_change_bit(long nr, volatile unsigned long *addr) */ static inline int test_and_change_bit(long nr, volatile unsigned long *addr) { - GEN_BINARY_RMWcc(LOCK_PREFIX "btc", *addr, nr, "%0", "c"); + GEN_BINARY_RMWcc(LOCK_PREFIX "btc", *addr, "Ir", nr, "%0", "c"); } static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr) diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h index 5b23e60..4ad6560 100644 --- a/arch/x86/include/asm/local.h +++ b/arch/x86/include/asm/local.h @@ -52,7 +52,7 @@ static inline void local_sub(long i, local_t *l) */ static inline int local_sub_and_test(long i, local_t *l) { - GEN_BINARY_RMWcc(_ASM_SUB, l->a.counter, i, "%0", "e"); + GEN_BINARY_RMWcc(_ASM_SUB, l->a.counter, "er", i, "%0", "e"); } /** @@ -92,7 +92,7 @@ static inline int local_inc_and_test(local_t *l) */ static inline int local_add_negative(long i, local_t *l) { - GEN_BINARY_RMWcc(_ASM_ADD, l->a.counter, i, "%0", "s"); + GEN_BINARY_RMWcc(_ASM_ADD, l->a.counter, "er", i, "%0", "s"); } /** diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h index 1ff990f..8f7866a 100644 --- a/arch/x86/include/asm/rmwcc.h +++ b/arch/x86/include/asm/rmwcc.h @@ -16,8 +16,8 @@ cc_label: \ #define GEN_UNARY_RMWcc(op, var, arg0, cc) \ __GEN_RMWcc(op " " arg0, var, cc) -#define GEN_BINARY_RMWcc(op, var, val, arg0, cc) \ - __GEN_RMWcc(op " %1, " arg0, var, cc, "er" (val)) +#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc) \ + __GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val)) #else /* !CC_HAVE_ASM_GOTO */ @@ -33,8 +33,8 @@ do { \ #define GEN_UNARY_RMWcc(op, var, arg0, cc) \ __GEN_RMWcc(op " " arg0, var, cc) -#define GEN_BINARY_RMWcc(op, var, val, arg0, cc) \ - __GEN_RMWcc(op " %2, " arg0, var, cc, "er" (val)) +#define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc) \ + __GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val)) #endif /* CC_HAVE_ASM_GOTO */ ^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2014-01-31 21:33 UTC | newest] Thread overview: 5+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2013-12-04 1:36 Regression due to 0c44c2d0f459 x86: Use asm goto to implement better modify_and_test() functions H. Peter Anvin 2013-12-04 8:59 ` Ingo Molnar 2013-12-04 16:44 ` H. Peter Anvin 2014-01-31 21:32 ` Alex Williamson 2013-12-04 22:51 ` [tip:x86/urgent] x86, bitops: Correct the assembly constraints to testing bitops tip-bot for H. Peter Anvin
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