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

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Message-ID: <Z8iccxCo7tkqvE_p@arm.com>
Date: Wed, 5 Mar 2025 18:48:19 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Piotr Jaroszynski <pjaroszynski@...dia.com>
Cc: Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	Robin Murphy <robin.murphy@....com>,
	Alistair Popple <apopple@...dia.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 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.

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