| Message ID | 20220810152033.946942-10-pgonda@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: selftests: Add simple SEV test | expand |
On Wed, Aug 10, 2022, Peter Gonda wrote: > atomic_test_and_set_bit() allows for atomic bitmap usage from KVM > selftests. > > Signed-off-by: Peter Gonda <pgonda@google.com> > Suggested-by: Sean Christopherson <seanjc@google.com> > --- > tools/arch/x86/include/asm/atomic.h | 7 +++++++ > tools/include/asm-generic/atomic-gcc.h | 15 +++++++++++++++ > 2 files changed, 22 insertions(+) > > diff --git a/tools/arch/x86/include/asm/atomic.h b/tools/arch/x86/include/asm/atomic.h > index 1f5e26aae9fc..01cc27ec4520 100644 > --- a/tools/arch/x86/include/asm/atomic.h > +++ b/tools/arch/x86/include/asm/atomic.h > @@ -8,6 +8,7 @@ > > #define LOCK_PREFIX "\n\tlock; " > > +#include <asm/asm.h> > #include <asm/cmpxchg.h> > > /* > @@ -70,4 +71,10 @@ static __always_inline int atomic_cmpxchg(atomic_t *v, int old, int new) > return cmpxchg(&v->counter, old, new); > } > > +static inline int atomic_test_and_set_bit(long nr, unsigned long *addr) > +{ > + GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(bts), *addr, "Ir", nr, "%0", "c"); > + Unnecessary newline. > +} > + > #endif /* _TOOLS_LINUX_ASM_X86_ATOMIC_H */ > diff --git a/tools/include/asm-generic/atomic-gcc.h b/tools/include/asm-generic/atomic-gcc.h > index 4c1966f7c77a..8d9b2d1768bf 100644 > --- a/tools/include/asm-generic/atomic-gcc.h > +++ b/tools/include/asm-generic/atomic-gcc.h > @@ -4,6 +4,7 @@ > > #include <linux/compiler.h> > #include <linux/types.h> > +#include <linux/bitops.h> > > /* > * Atomic operations that C can't guarantee us. Useful for > @@ -69,4 +70,18 @@ static inline int atomic_cmpxchg(atomic_t *v, int oldval, int newval) > return cmpxchg(&(v)->counter, oldval, newval); > } > +static inline int atomic_test_and_set_bit(long nr, unsigned long *addr) > +{ > + long old, val; > + unsigned long mask = BIT_MASK(nr); > + > + addr += BIT_WORD(nr); > + val = READ_ONCE(*addr); > + if (val & mask) > + return 1; Probably should drop the READ_ONCE() shortcut to stay consistent with the kernel proper. https://lore.kernel.org/all/CAHk-=wgSNiT5qJX53RHtWECsUiFq6d6VWYNAvu71ViOEan07yw@mail.gmail.com > + > + old = cmpxchg(addr, val, val & mask); This is wrong on two fronts: 1) cmpxchg() writes the entire new value, and 2) it fails if the old value is not an exact match with what's in memory. Bug #1 means that setting a bit will clear all existing bits, and bug #2 means that this will fail to set the bit if another atomic_test_and_set_bit() sneaks in between reading into "val" and doing the cmpxchg. And obviously dropping the READ_ONCE() above makes cmpxchg impossible (not a coincidence, it's simply the wrong operation to use). I believe what we want is: unsigned long mask = BIT_MASK(nr); long old; old = __sync_fetch_and_or(addr, mask); return !!(old & mask); > + return !!(old & mask); > +} > + > #endif /* __TOOLS_ASM_GENERIC_ATOMIC_H */ > -- > 2.37.1.559.g78731f0fdb-goog >
diff --git a/tools/arch/x86/include/asm/atomic.h b/tools/arch/x86/include/asm/atomic.h index 1f5e26aae9fc..01cc27ec4520 100644 --- a/tools/arch/x86/include/asm/atomic.h +++ b/tools/arch/x86/include/asm/atomic.h @@ -8,6 +8,7 @@ #define LOCK_PREFIX "\n\tlock; " +#include <asm/asm.h> #include <asm/cmpxchg.h> /* @@ -70,4 +71,10 @@ static __always_inline int atomic_cmpxchg(atomic_t *v, int old, int new) return cmpxchg(&v->counter, old, new); } +static inline int atomic_test_and_set_bit(long nr, unsigned long *addr) +{ + GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(bts), *addr, "Ir", nr, "%0", "c"); + +} + #endif /* _TOOLS_LINUX_ASM_X86_ATOMIC_H */ diff --git a/tools/include/asm-generic/atomic-gcc.h b/tools/include/asm-generic/atomic-gcc.h index 4c1966f7c77a..8d9b2d1768bf 100644 --- a/tools/include/asm-generic/atomic-gcc.h +++ b/tools/include/asm-generic/atomic-gcc.h @@ -4,6 +4,7 @@ #include <linux/compiler.h> #include <linux/types.h> +#include <linux/bitops.h> /* * Atomic operations that C can't guarantee us. Useful for @@ -69,4 +70,18 @@ static inline int atomic_cmpxchg(atomic_t *v, int oldval, int newval) return cmpxchg(&(v)->counter, oldval, newval); } +static inline int atomic_test_and_set_bit(long nr, unsigned long *addr) +{ + long old, val; + unsigned long mask = BIT_MASK(nr); + + addr += BIT_WORD(nr); + val = READ_ONCE(*addr); + if (val & mask) + return 1; + + old = cmpxchg(addr, val, val & mask); + return !!(old & mask); +} + #endif /* __TOOLS_ASM_GENERIC_ATOMIC_H */
atomic_test_and_set_bit() allows for atomic bitmap usage from KVM selftests. Signed-off-by: Peter Gonda <pgonda@google.com> Suggested-by: Sean Christopherson <seanjc@google.com> --- tools/arch/x86/include/asm/atomic.h | 7 +++++++ tools/include/asm-generic/atomic-gcc.h | 15 +++++++++++++++ 2 files changed, 22 insertions(+)