Hi Catalin, > On Tue, Feb 10, 2026 at 05:01:33PM +0000, Yeoreum Yun wrote: > > > Why not keep uaccess_enable_privileged() in > > > arch_futex_atomic_op_inuser() and cmpxchg for all cases and make it a > > > no-op if FEAT_LSUI is implemented together with FEAT_PAN? > > > > This is because I had a assumption FEAT_PAN must be present > > when FEAT_LSUI is presented and this was not considering the virtualisation > > case. > > and FEAT_PAN is present uaccess_ttbr0_enable() becomes nop and > > following feedback you gave - > > https://lore.kernel.org/all/[email protected]/ > > and the reason you mention last, It doesn't need to call mte_enable_tco(). > > > > That's why I thought it doesn't need to call uaccess_enable_privileged(). > > > > But for a compatibility with SW_PAN, I think we can put only > > uaccess_ttbr0_enable() in arch_futex_atomic_op_inuser() and cmpxchg simply > > instead of adding a new APIs uaccess_enable_futex() and > > by doing this I think has_lsui() can be removed with its WRAN. > > Yes, I think you can use uaccess_ttbr0_enable() when we take the > FEAT_LSUI path. What I meant above was for uaccess_enable_privileged() > to avoid PAN disabling if we have FEAT_LSUI as we know all cases would > be executed with user privileges. > > Either way, we don't need a new uaccess_enable_futex().
Yes. But like raw_copy_from/to_user() where use ldtr*/sttr* when MOPS isn't enabled, It seems better to use uaccess_ttbr0_enable() instead of making special handling for LSUI in uaccess_enable_privileged(). This seems more consistent since ldtr*/sttr* are similar function of LSUI (doesn't disable PAN) and doesn't enable mto. > > > > BTW, with the removal of uaccess_enable_privileged(), we now get MTE tag > > > checks for the futex operations. I think that's good as it matches the > > > other uaccess ops, though it's a slight ABI change. If we want to > > > preserve the old behaviour, we definitely need > > > uaccess_enable_privileged() that only does mte_enable_tco(). > > > > I think we don't need to preserve the old behaviour. so we can skip > > mte_enable_tco() in case of FEAT_LSUI is presented. > > Just spell it out in the commit log that we have a slight ABI change. I > don't think we'll have a problem but it needs at least checking with > some user-space (libc, Android) people. I see. Thanks! > > -- > Catalin -- Sincerely, Yeoreum Yun
