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

[Thomas Gleixner <tglx@kernel.org>]

On Wed, May 27 2026 at 22:02, André Almeida wrote:

> 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@kernel.org>
>
> [...]
>
>> +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@t-8ch.de/

Sure. Let me change that.