Re: [PATCH] arm64: suspend: Save and restore TPIDR2_EL0 across CPU suspend

[Wei Wang]

On Tue, Nov 3, 2026 at 7:49 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
>
> On Tue, Nov 03, 2026 at 11:50:03AM +0000, Will Deacon wrote:
> > On Mon, Nov 02, 2026 at 11:48:13PM +0000, Wei Wang wrote:
> > > On systems with FEAT_SME, TPIDR2_EL0 is part of userspace thread state:
> > > the AAPCS64 SME ABI uses it as the ZA lazy-save pointer, and the kernel
> > > context-switches it eagerly in tls_thread_switch(). While a task is
> > > running, the live register is the only copy of its value.
>
> [...]
>
> > There's a lot of unnecessary (AI-generated?) detail in here. Please can
> > you trim this down a bit? I don't think we care about the firmware part,
> > the stuff about idle or the bionic crash. The bottom line is that we're
> > not saving/restoring a live EL0 register across suspend/resume.
>
> I should get an LLM to trim it down when applying ;).
>

Fair point, I'll send a v2 with a trimmed commit message.

> > > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> > > index 7afbece885a3..c7b7fa6491c3 100644
> > > --- a/arch/arm64/mm/proc.S
> > > +++ b/arch/arm64/mm/proc.S
> > > @@ -103,6 +103,10 @@ SYM_FUNC_START(cpu_do_suspend)
> > >  alternative_if ARM64_HAS_TCR2
> > >     mrs     x2, REG_TCR2_EL1
> > >     str     x2, [x0, #104]
> > > +alternative_else_nop_endif
> > > +alternative_if ARM64_SME
> > > +   mrs_s   x2, SYS_TPIDR2_EL0
> > > +   str     x2, [x0, #112]
> > >  alternative_else_nop_endif
> > >     ret
> > >  SYM_FUNC_END(cpu_do_suspend)
> > > @@ -142,6 +146,10 @@ alternative_if ARM64_HAS_TCR2
> > >     ldr     x2, [x0, #104]
> > >     msr     REG_TCR2_EL1, x2
> > >  alternative_else_nop_endif
> > > +alternative_if ARM64_SME
> > > +   ldr     x2, [x0, #112]
> > > +   msr_s   SYS_TPIDR2_EL0, x2
> > > +alternative_else_nop_endif
> >
> > nit: We use msr and REG_* for TCR2, so it would be more consistent to do
> > the same for TPIDR2_EL0 if the assembler is happy with it.
>
> TPIDR2 is not defined in arch/arm64/tools/sysreg yet (for some reason,
> only TPIDR_EL1 is). Since this is a cc stable, I think we can leave it
> as is and do a TPIDR* cleanup going forward.
>
> --
> Catalin