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V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Catalin Marinas , Paul Walmsley , Palmer Dabbelt , Albert Ou , Arnd Bergmann , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Nadav Amit , Andrea Arcangeli , Andy Lutomirski , Dave Hansen , Thomas Gleixner , Yu Zhao , x86@kernel.org Subject: Re: [PATCH 1/2] mm/tlb: fix fullmm semantics Message-ID: <20240103175743.GG5954@willie-the-truck> References: <20231228084642.1765-1-jszhang@kernel.org> <20231228084642.1765-2-jszhang@kernel.org> <20240103175001.GF5954@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240103175001.GF5954@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 25F23A001A X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 1f9858aewqtodt93a8q7xe6iejrjd11r X-HE-Tag: 1704304674-671733 X-HE-Meta: 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 OK5TYGAG NnNdcyhndmjCsCUeFv44C1kNG1TisDYBeaCNbduzSHmw8hlgfG8OWTUhcZLFmI9Guh9Jm7jYNQr2HuBUL5uBc4ExMoQNRTmFKwc+q6hmYIxArqvFXG28cL8zDLkT7igG3zHq+7wXpShdpTUI4z4iKF8hRiwHUVqsXh669wnXhApsZN+456EfvWrUtb6bFRCIm7ExbABS4WzZNpCnba6g4uySiqIDY+hJqUiagkD0h0ZpC5sHMRGXpoycEh7JnJaSFadDjCuIQaCEbwNZHE5a2ebeaBGDumeSF9x0lDkUHKKsCG6xheaS1eWSOW//W+CFpa5WGZMKeE1DRzMeqo0IvoWgpeACjNxb6IAa5ejivxA7FWubYnZ9eJYxeix38V4SjxlZot8Vn2V+3lheB0+ZGZhOlkeMFXyOfm7glHyaWjphRLLz25CBBOHA8goPqaOu5jL2gqeG7GZu5/vUeMUO1eQIiE+AIRCvj9Skzw5tnsBcWbM8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jan 03, 2024 at 05:50:01PM +0000, Will Deacon wrote: > On Thu, Dec 28, 2023 at 04:46:41PM +0800, Jisheng Zhang wrote: > > From: Nadav Amit > > > > fullmm in mmu_gather is supposed to indicate that the mm is torn-down > > (e.g., on process exit) and can therefore allow certain optimizations. > > However, tlb_finish_mmu() sets fullmm, when in fact it want to say that > > the TLB should be fully flushed. > > > > Change tlb_finish_mmu() to set need_flush_all and check this flag in > > tlb_flush_mmu_tlbonly() when deciding whether a flush is needed. > > > > At the same time, bring the arm64 fullmm on process exit optimization back. > > > > Signed-off-by: Nadav Amit > > Signed-off-by: Jisheng Zhang > > Cc: Andrea Arcangeli > > Cc: Andrew Morton > > Cc: Andy Lutomirski > > Cc: Dave Hansen > > Cc: Peter Zijlstra > > Cc: Thomas Gleixner > > Cc: Will Deacon > > Cc: Yu Zhao > > Cc: Nick Piggin > > Cc: x86@kernel.org > > --- > > arch/arm64/include/asm/tlb.h | 5 ++++- > > include/asm-generic/tlb.h | 2 +- > > mm/mmu_gather.c | 2 +- > > 3 files changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > > index 846c563689a8..6164c5f3b78f 100644 > > --- a/arch/arm64/include/asm/tlb.h > > +++ b/arch/arm64/include/asm/tlb.h > > @@ -62,7 +62,10 @@ static inline void tlb_flush(struct mmu_gather *tlb) > > * invalidating the walk-cache, since the ASID allocator won't > > * reallocate our ASID without invalidating the entire TLB. > > */ > > - if (tlb->fullmm) { > > + if (tlb->fullmm) > > + return; > > + > > + if (tlb->need_flush_all) { > > if (!last_level) > > flush_tlb_mm(tlb->mm); > > return; > > Why isn't the 'last_level' check sufficient here? In other words, when do > we perform a !last_level invalidation with 'fullmm' set outside of teardown? Sorry, logic inversion typo there. I should've said: When do we perform a last_level invalidation with 'fullmm' set outside of teardown? I remember this used to be the case for OOM ages ago, but 687cb0884a71 ("mm, oom_reaper: gather each vma to prevent leaking TLB entry") sorted that out. I'm not against making this clearer and/or more robust, I'm just trying to understand whether this is fixing a bug (as implied by the subject) or not. Will