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

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Message-ID: <20250305193551.GB32246@willie-the-truck>
Date: Wed, 5 Mar 2025 19:35:52 +0000
From: Will Deacon <will@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Piotr Jaroszynski <pjaroszynski@...dia.com>,
	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 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.
> 
> 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.

Yeah, I'll pick it up but I'm travelling atm so it may have to wait until
next week.

Will