Re: [GIT PULL] RISC-V updates for v7.0

[Deepak Gupta <debug@rivosinc.com>]

On Thu, Feb 19, 2026 at 12:01:10AM +0000, Mark Brown wrote:
>On Wed, Feb 18, 2026 at 09:58:41PM +0000, Edgecombe, Rick P wrote:
>> On Wed, 2026-02-18 at 11:57 -0800, Deepak Gupta wrote:
>
>> > If we land arch-agnostic prctl for enabling branch tracking for userspace as
>> > part of risc-v patches, I am hoping we can leverage that for x86 "branch
>> > tracking enabling" as well. I don't know if "BTI" is enabled for userspace in
>> > the arm64 world but if it isn't then it can use the same prctl. This creates
>> > symmetry and convergence as well between major 3 arches for branch tracking
>> > support.
>
>BTI has been available to userspace for quite a while now.

Noted.

>
>> Arm already uses PROT_BTI to enable their landing pad like thing. It doesn't
>> need a prctl AFAIU. Peterz had been suggesting we do a similar PROT for x86 user
>> IBT. Although an additional prctl might still be required for x86. We'd have to
>> actually start taking the patches upstream to see.
>
>Yeah, for arm64 BTI the control is all per page rather than per thread
>or process.  Unless I'm forgetting something there's just not a global
>control for this in the hardware, it's all keyed off the page tables.

Aah this makes sense. This is different from x86 and risc-v. Since BTI is on
per-code page basis, kernel enables if loader (interpreter for executable) and
then likely loader sets PROT_BTI for rest of the user space dependencies.