linux-kernel - Re: [PATCH] [arm64/tlb] Fix mmu notifiers for range-based invalidates

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Message-ID: <3wosp7lqbcwzspgv7gq25ii5hdr3fztrvnhcha3uqcyellulro@xyz7gx7qjkq2>
Date: Thu, 6 Mar 2025 10:49:30 +1100
From: Alistair Popple <apopple@...dia.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Piotr Jaroszynski <pjaroszynski@...dia.com>, 
	Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	Robin Murphy <robin.murphy@....com>, Raghavendra Rao Ananta <rananta@...gle.com>, 
	SeongJae Park <sj@...nel.org>, Jason Gunthorpe <jgg@...dia.com>, 
	John Hubbard <jhubbard@...dia.com>, Nicolin Chen <nicolinc@...dia.com>, iommu@...ts.linux.dev, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] [arm64/tlb] Fix mmu notifiers for range-based invalidates

On Wed, Mar 05, 2025 at 06:48:19PM +0000, Catalin Marinas wrote:
> On Tue, Mar 04, 2025 at 12:51:27AM -0800, Piotr Jaroszynski wrote:
> > Update the __flush_tlb_range_op macro not to modify its parameters as
> > these are unexepcted semantics. In practice, this fixes the call to
> > mmu_notifier_arch_invalidate_secondary_tlbs() in
> > __flush_tlb_range_nosync() to use the correct range instead of an empty
> > range with start=end. The empty range was (un)lucky as it results in
> > taking the invalidate-all path that doesn't cause correctness issues,
> > but can certainly result in suboptimal perf.
> > 
> > This has been broken since commit 6bbd42e2df8f ("mmu_notifiers: call
> > invalidate_range() when invalidating TLBs") when the call to the
> > notifiers was added to __flush_tlb_range(). It predates the addition of
> > the __flush_tlb_range_op() macro from commit 360839027a6e ("arm64: tlb:
> > Refactor the core flush algorithm of __flush_tlb_range") that made the
> > bug hard to spot.
> 
> That's the problem with macros.

Yep, that's why I missed it when adding the notifier call. Anyway:

Reviewed-by: Alistair Popple <apopple@...dia.com>

> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> 
> Will, do you want to take this as a fix? It's only a performance
> regression, though you never know how it breaks the callers of the macro
> at some point.
> 
> > Fixes: 6bbd42e2df8f ("mmu_notifiers: call invalidate_range() when invalidating TLBs")
> > 
> > Signed-off-by: Piotr Jaroszynski <pjaroszynski@...dia.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Cc: Alistair Popple <apopple@...dia.com>
> > Cc: Raghavendra Rao Ananta <rananta@...gle.com>
> > Cc: SeongJae Park <sj@...nel.org>
> > Cc: Jason Gunthorpe <jgg@...dia.com>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: Nicolin Chen <nicolinc@...dia.com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: iommu@...ts.linux.dev
> > Cc: linux-mm@...ck.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: stable@...r.kernel.org
> > ---
> >  arch/arm64/include/asm/tlbflush.h | 22 ++++++++++++----------
> >  1 file changed, 12 insertions(+), 10 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> > index bc94e036a26b..8104aee4f9a0 100644
> > --- a/arch/arm64/include/asm/tlbflush.h
> > +++ b/arch/arm64/include/asm/tlbflush.h
> > @@ -396,33 +396,35 @@ static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
> >  #define __flush_tlb_range_op(op, start, pages, stride,			\
> >  				asid, tlb_level, tlbi_user, lpa2)	\
> >  do {									\
> > +	typeof(start) __flush_start = start;				\
> > +	typeof(pages) __flush_pages = pages;				\
> >  	int num = 0;							\
> >  	int scale = 3;							\
> >  	int shift = lpa2 ? 16 : PAGE_SHIFT;				\
> >  	unsigned long addr;						\
> >  									\
> > -	while (pages > 0) {						\
> > +	while (__flush_pages > 0) {					\
> >  		if (!system_supports_tlb_range() ||			\
> > -		    pages == 1 ||					\
> > -		    (lpa2 && start != ALIGN(start, SZ_64K))) {		\
> > -			addr = __TLBI_VADDR(start, asid);		\
> > +		    __flush_pages == 1 ||				\
> > +		    (lpa2 && __flush_start != ALIGN(__flush_start, SZ_64K))) {	\
> > +			addr = __TLBI_VADDR(__flush_start, asid);	\
> >  			__tlbi_level(op, addr, tlb_level);		\
> >  			if (tlbi_user)					\
> >  				__tlbi_user_level(op, addr, tlb_level);	\
> > -			start += stride;				\
> > -			pages -= stride >> PAGE_SHIFT;			\
> > +			__flush_start += stride;			\
> > +			__flush_pages -= stride >> PAGE_SHIFT;		\
> >  			continue;					\
> >  		}							\
> >  									\
> > -		num = __TLBI_RANGE_NUM(pages, scale);			\
> > +		num = __TLBI_RANGE_NUM(__flush_pages, scale);		\
> >  		if (num >= 0) {						\
> > -			addr = __TLBI_VADDR_RANGE(start >> shift, asid, \
> > +			addr = __TLBI_VADDR_RANGE(__flush_start >> shift, asid, \
> >  						scale, num, tlb_level);	\
> >  			__tlbi(r##op, addr);				\
> >  			if (tlbi_user)					\
> >  				__tlbi_user(r##op, addr);		\
> > -			start += __TLBI_RANGE_PAGES(num, scale) << PAGE_SHIFT; \
> > -			pages -= __TLBI_RANGE_PAGES(num, scale);	\
> > +			__flush_start += __TLBI_RANGE_PAGES(num, scale) << PAGE_SHIFT; \
> > +			__flush_pages -= __TLBI_RANGE_PAGES(num, scale);\
> >  		}							\
> >  		scale--;						\
> >  	}								\
> > 
> > base-commit: 99fa936e8e4f117d62f229003c9799686f74cebc
> > -- 
> > 2.22.1.7.gac84d6e93c.dirty
> 
> -- 
> Catalin