On 27/01/2026 15:03, Ard Biesheuvel wrote: > On Tue, 27 Jan 2026 at 10:45, Ryan Roberts <[email protected]> wrote: >> >> On 26/01/2026 09:26, Ard Biesheuvel wrote: >>> From: Ard Biesheuvel <[email protected]> >>> >>> Currently, pgattr_change_is_safe() is overly pedantic when it comes to >>> descriptors with the contiguous hint attribute set, as it rejects >>> assignments even if the old and the new value are the same. >>> >>> So relax the check to allow that. >> >> But why do we require the relaxation? Why are we re-writing a PTE in the >> first >> place? Either the caller already knows it's the same in which case it can be >> avoided, or it doesn't know in which case it is accidentally the same and >> couple >> probably just as easily been accidentally different? So it's better to warn >> regardless I would think? >> > > Based on rule RJQQTC in your reply to another patch in this series, my > conclusion here is that we can drop this check entirely.
Hmm, I don't think that would be quite right; The rule permits _some_ bits of the PTE to change in a live mapping as long as the CONT bit remains unchanged. If you change the CONT bit on a live mapping, you could end up with overlapping TLB entries which would not go well on a system without bbml2.
