Re: [PATCH v8 4/4] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

[André Almeida]

Em 16/09/2026 11:28, Mark Rutland escreveu:
> On Fri, Aug 21, 2026 at 06:50:45PM -0300, André Almeida wrote:
> > Based on aarch64 implementation, provide a 32 bit entry point for
> > this vDSO.
> >
> > In order to keep compatibility with arm64_futex_robust_unlock_get_pop(),
> > make sure to store the pop address at r2 and the compare result value
> > at r3.
>
> Before we add this to the compat vdso, we'll need to implement this on
> arch/arm/.
>
> Otherwise, my comments on the patch for the native vdso functions apply
> here too.

Right, and the compat entry point at arch/arm64/ would point to the 
__vdso_futex_robust_list32_try_unlock implementation at arch/arm/?

> Mark.
>
> > Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> > ---
> > v7:
> >   - The store needs to be a release store, so s/strex/stlex/
> >   - result reg clobber modified to "=&r" to make sure the compiler don't use
> >   the r3 reg for something else
> >   - pop_reg will be read after the execution so it should be an output
> >   parameter with "+Q"
> > ---
> >   arch/arm64/kernel/vdso.c            | 15 ++++++++++++++-
> >   arch/arm64/kernel/vdso32/Makefile   |  4 ++++
> >   arch/arm64/kernel/vdso32/vdso.lds.S |  9 +++++++++
> >   arch/arm64/kernel/vdso32/vfutex.c   | 34 ++++++++++++++++++++++++++++++++++
> >   4 files changed, 61 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> > index dc6b582736d0..5cae9c17ec72 100644
> > --- a/arch/arm64/kernel/vdso.c
> > +++ b/arch/arm64/kernel/vdso.c
> > @@ -78,11 +78,19 @@ static inline void vdso_futex_update_ips(struct mm_struct *mm)
> >   				VDSO_SYMBOL(vdso, futex_list64_try_unlock_cs_end));
> >   }
> >   
> > +static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm)
> > +{
> > +	unsigned long vdso = (unsigned long) mm->context.vdso;
> > +
> > +	__vdso_futex_update_ips(mm, true,
> > +				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_start),
> > +				VDSO_SYMBOL(vdso, futex_list32_try_unlock_cs_end));
> > +}
> >   #else
> >   static inline void vdso_futex_update_ips(struct mm_struct *mm) {}
> > +static inline void aarch32_vdso_futex_update_ips(struct mm_struct *mm) {}
> >   #endif /* CONFIG_FUTEX_ROBUST_UNLOCK */
> >   
> > -
> >   static int vdso_mremap(const struct vm_special_mapping *sm,
> >   		struct vm_area_struct *new_vma)
> >   {
> > @@ -195,6 +203,8 @@ static int aarch32_mremap(const struct vm_special_mapping *sm,
> >   {
> >   	current->mm->context.vdso = (void *)new_vma->vm_start;
> >   
> > +	aarch32_vdso_futex_update_ips(current->mm);
> > +
> >   	return 0;
> >   }
> >   
> > @@ -327,6 +337,7 @@ static int aarch32_sigreturn_setup(struct mm_struct *mm)
> >   	return PTR_ERR_OR_ZERO(ret);
> >   }
> >   
> > +
> >   int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> >   {
> >   	struct mm_struct *mm = current->mm;
> > @@ -347,6 +358,8 @@ int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> >   	}
> >   
> >   	ret = aarch32_sigreturn_setup(mm);
> > +
> > +	aarch32_vdso_futex_update_ips(mm);
> >   out:
> >   	mmap_write_unlock(mm);
> >   	return ret;
> > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> > index 4bd60f059f4a..f3190125c68b 100644
> > --- a/arch/arm64/kernel/vdso32/Makefile
> > +++ b/arch/arm64/kernel/vdso32/Makefile
> > @@ -97,6 +97,10 @@ munge := ../../../arm/vdso/vdsomunge
> >   hostprogs := $(munge)
> >   
> >   c-obj-vdso := note.o
> > +ifdef CONFIG_FUTEX_ROBUST_UNLOCK
> > +  c-obj-vdso += vfutex.o
> > +endif
> > +
> >   c-obj-vdso-gettimeofday := vgettimeofday.o
> >   
> >   ifneq ($(c-gettimeofday-y),)
> > diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
> > index 12bfc39e8aab..52ced27d6045 100644
> > --- a/arch/arm64/kernel/vdso32/vdso.lds.S
> > +++ b/arch/arm64/kernel/vdso32/vdso.lds.S
> > @@ -89,6 +89,15 @@ VERSION
> >   #endif /* CONFIG_COMPAT_32BIT_TIME */
> >   		__vdso_clock_gettime64;
> >   		__vdso_clock_getres_time64;
> > +#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
> > +		__vdso_futex_robust_list32_try_unlock;
> > +#endif
> >   	local: *;
> >   	};
> >   }
> > +
> > +#ifdef CONFIG_FUTEX_ROBUST_UNLOCK
> > +VDSO_futex_list32_try_unlock_cs_success = __futex_list32_try_unlock_cs_success;
> > +VDSO_futex_list32_try_unlock_cs_start = __futex_list32_try_unlock_cs_start;
> > +VDSO_futex_list32_try_unlock_cs_end = __futex_list32_try_unlock_cs_end;
> > +#endif
> > diff --git a/arch/arm64/kernel/vdso32/vfutex.c b/arch/arm64/kernel/vdso32/vfutex.c
> > new file mode 100644
> > index 000000000000..0d9080b17965
> > --- /dev/null
> > +++ b/arch/arm64/kernel/vdso32/vfutex.c
> > @@ -0,0 +1,34 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +#include <linux/stringify.h>
> > +#include <vdso/futex.h>
> > +
> > +__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop)
> > +{
> > +	register __u32 *pop_reg asm("r2") = pop, result_reg asm("r3") = 0;
> > +	__u32 val, zero = 0;
> > +
> > +	asm volatile (
> > +		".globl						  "
> > +		"__futex_list32_try_unlock_cs_start,		  "
> > +		"__futex_list32_try_unlock_cs_success,		  "
> > +		"__futex_list32_try_unlock_cs_end		\n"
> > +
> > +		"retry:						\n"
> > +		"	ldrex %[val], %[lock]			\n"
> > +		"	cmp %[tid], %[val]			\n"
> > +		"	bne __futex_list32_try_unlock_cs_end	\n"
> > +		"	stlex %[result], %[zero], %[lock]	\n"
> > +		"__futex_list32_try_unlock_cs_start:		\n"
> > +		"	cmp %[result], #0			\n"
> > +		"	bne retry				\n"
> > +		"__futex_list32_try_unlock_cs_success:		\n"
> > +		"	str %[zero], %[pop_reg]			\n"
> > +		"__futex_list32_try_unlock_cs_end:		\n"
> > +
> > +		: [val] "=&r" (val), [result] "=&r" (result_reg), [pop_reg] "+Q" (*pop_reg)
> > +		: [tid] "r" (tid), [lock] "Q" (*lock), [zero] "r" (zero)
> > +		: "cc", "memory"
> > +	);
> > +
> > +	return val;
> > +}
> >
> > --
> > 2.55.0