Re: [patch V4 09/14] futex: Add robust futex unlock IP range

[André Almeida]

Em 02/04/2026 12:21, Thomas Gleixner escreveu:
> There will be a VDSO function to unlock robust futexes in user space. The
> unlock sequence is racy vs. clearing the list_pending_op pointer in the
> tasks robust list head. To plug this race the kernel needs to know the
> instruction window. As the VDSO is per MM the addresses are stored in
> mm_struct::futex.
>
> Architectures which implement support for this have to update these
> addresses when the VDSO is (re)mapped and indicate the pending op pointer
> size which is matching the IP.
>
> Arguably this could be resolved by chasing mm->context->vdso->image, but
> that's architecture specific and requires to touch quite some cache
> lines. Having it in mm::futex reduces the cache line impact and avoids
> having yet another set of architecture specific functionality.
>
> To support multi size robust list applications (gaming) this provides two
> ranges when COMPAT is enabled.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>

[...]

> +void futex_reset_cs_ranges(struct futex_mm_data *fd);
> +
> +static inline void futex_set_vdso_cs_range(struct futex_mm_data *fd, unsigned int idx,
> +					   unsigned long vdso, unsigned long start,
> +					   unsigned long end, bool sz32)
> +{
> +	fd->unlock.cs_ranges[idx].start_ip = vdso + start;
> +	fd->unlock.cs_ranges[idx].len = end - start;
> +	fd->unlock.cs_ranges[idx].pop_size32 = sz32;
> +}

Can we have the "vdso +" done by the caller? VDSO_SYMBOL() that I used 
for aarch64 adds the base address as well, see here: 
https://lore.kernel.org/lkml/f8e83a24-0b04-4c88-9f67-0879875be25c@xxxxxxxx/

Apart from that:
	Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxx>