Re: [PATCH 2/4] arm64: tlb: Pass the corresponding mm to __tlbi_sync_s1ish()

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Mar 05, 2026 at 02:33:18PM +0000, Will Deacon wrote:
> On Mon, Mar 02, 2026 at 04:57:55PM +0000, Catalin Marinas wrote:
> > The mm structure will be used for workarounds that need limiting to
> > specific tasks.
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > ---
> >  arch/arm64/include/asm/tlbflush.h | 10 +++++-----
> >  arch/arm64/kernel/sys_compat.c    |  2 +-
> >  2 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> > index 19be0f7bfca5..14f116bfec73 100644
> > --- a/arch/arm64/include/asm/tlbflush.h
> > +++ b/arch/arm64/include/asm/tlbflush.h
> > @@ -185,7 +185,7 @@ do {										\
> >   * Complete broadcast TLB maintenance issued by the host which invalidates
> >   * stage 1 information in the host's own translation regime.
> >   */
> > -static inline void __tlbi_sync_s1ish(void)
> > +static inline void __tlbi_sync_s1ish(struct mm_struct *mm)
> >  {
> >  	dsb(ish);
> >  	__repeat_tlbi_sync(vale1is, 0);
> > @@ -317,7 +317,7 @@ static inline void flush_tlb_mm(struct mm_struct *mm)
> >  	asid = __TLBI_VADDR(0, ASID(mm));
> >  	__tlbi(aside1is, asid);
> >  	__tlbi_user(aside1is, asid);
> > -	__tlbi_sync_s1ish();
> > +	__tlbi_sync_s1ish(mm);
> >  	mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL);
> >  }
> >  
> > @@ -371,7 +371,7 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
> >  				  unsigned long uaddr)
> >  {
> >  	flush_tlb_page_nosync(vma, uaddr);
> > -	__tlbi_sync_s1ish();
> > +	__tlbi_sync_s1ish(vma->vm_mm);
> >  }
> >  
> >  static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> > @@ -391,7 +391,7 @@ static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> >   */
> >  static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
> >  {
> > -	__tlbi_sync_s1ish();
> > +	__tlbi_sync_s1ish(NULL);
> 
> Hmm, it seems a bit rubbish to pass NULL here as that means that we'll
> deploy the mitigation regardless of the mm flags when finishing the
> batch.
> 
> It also looks like we could end up doing the workaround multiple times
> if arch_tlbbatch_add_pending() is passed a large enough region that we
> call __flush_tlb_range_limit_excess() fires.
> 
> So perhaps we should stash the mm in 'struct arch_tlbflush_unmap_batch'
> alongside some state to track whether or not we have uncompleted TLB
> maintenance in flight?

The problem is that arch_tlbbatch_flush() can be called to synchronise
multiple mm structures that were touched by TTU. We can't have the mm in
arch_tlbflush_unmap_batch. But we can track if any of the mms had
MMCF_SME_DVMSYNC flag set, something like below (needs testing, tidying
up). TBH, I did not notice any problem in benchmarking as I guess we
haven't exercised the TTU path much, so did not bother to optimise it.

For the TTU case, I don't think we need to worry about the excess limit
and doing the IPI twice. But I'll double check the code paths tomorrow.

diff --git a/arch/arm64/include/asm/tlbbatch.h b/arch/arm64/include/asm/tlbbatch.h
index fedb0b87b8db..e756eaca6cb8 100644
--- a/arch/arm64/include/asm/tlbbatch.h
+++ b/arch/arm64/include/asm/tlbbatch.h
@@ -7,6 +7,8 @@ struct arch_tlbflush_unmap_batch {
 	 * For arm64, HW can do tlb shootdown, so we don't
 	 * need to record cpumask for sending IPI
 	 */
+
+	bool sme_dvmsync;
 };

 #endif /* _ARCH_ARM64_TLBBATCH_H */
diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
index e3ea0246a4f4..c1141a684854 100644
--- a/arch/arm64/include/asm/tlbflush.h
+++ b/arch/arm64/include/asm/tlbflush.h
@@ -201,10 +201,15 @@ do {										\
  * Complete broadcast TLB maintenance issued by the host which invalidates
  * stage 1 information in the host's own translation regime.
  */
-static inline void __tlbi_sync_s1ish(struct mm_struct *mm)
+static inline void __tlbi_sync_s1ish_no_sme_dvmsync(void)
 {
 	dsb(ish);
 	__repeat_tlbi_sync(vale1is, 0);
+}
+
+static inline void __tlbi_sync_s1ish(struct mm_struct *mm)
+{
+	__tlbi_sync_s1ish_no_sme_dvmsync();
 	sme_dvmsync(mm);
 }

@@ -408,7 +413,11 @@ static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
  */
 static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
 {
-	__tlbi_sync_s1ish(NULL);
+	__tlbi_sync_s1ish_no_sme_dvmsync();
+	if (batch->sme_dvmsync) {
+		batch->sme_dvmsync = false;
+		sme_dvmsync(NULL);
+	}
 }

 /*
@@ -613,6 +622,8 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b
 		struct mm_struct *mm, unsigned long start, unsigned long end)
 {
 	__flush_tlb_range_nosync(mm, start, end, PAGE_SIZE, true, 3);
+	if (test_bit(ilog2(MMCF_SME_DVMSYNC), &mm->context.flags))
+		batch->sme_dvmsync = true;
 }

 static inline bool __pte_flags_need_flush(ptdesc_t oldval, ptdesc_t newval)