From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 57BF557861; Tue, 30 Jan 2024 08:45:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706604351; cv=none; b=NvDhH/+bLjIB+1PSiiikbLNmiZ/B9fb/1EHI2t8CzavBecy5LH4rzDHzagWmvzLVLTL/jEeyF7HNbQAQvMQ0fXGneqQlGVJRk+kKpzKlVKADOnJQz3zPSFn4FXwxDF2D5ggHjda76Ip0fum+izUxzPmQiONPEBvSizDCUapWHLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706604351; c=relaxed/simple; bh=YPivXGUwsgxM6K1OyqG9VqP6YDZRo0TgVHoytzvbpTk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LBkSOvvy0GeFekgq5cJaCG9J1F1DTM8foyah8TljxyjFB8LFTp9IzAKORRZlwDpDFRFB+7ViSK6iuQmRLUikuWkPih5nz5mqPhbSaRPp1mm5rcp10c3eS6g5cpMD6+M33Ex0MHI2lTFKsrzQpvXaGtuehgPgpOo/MjhaWkr+tok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 600E3DA7; Tue, 30 Jan 2024 00:46:31 -0800 (PST) Received: from [10.57.79.54] (unknown [10.57.79.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8B93E3F738; Tue, 30 Jan 2024 00:45:43 -0800 (PST) Message-ID: Date: Tue, 30 Jan 2024 08:45:41 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 3/9] mm/memory: further separate anon and pagecache folio handling in zap_present_pte() Content-Language: en-GB To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Catalin Marinas , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Michael Ellerman , Christophe Leroy , "Naveen N. Rao" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org References: <20240129143221.263763-1-david@redhat.com> <20240129143221.263763-4-david@redhat.com> <40cfb242-ceb0-44c6-afe7-c1744825dc62@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 30/01/2024 08:37, David Hildenbrand wrote: > On 30.01.24 09:31, Ryan Roberts wrote: >> On 29/01/2024 14:32, David Hildenbrand wrote: >>> We don't need up-to-date accessed-dirty information for anon folios and can >>> simply work with the ptent we already have. Also, we know the RSS counter >>> we want to update. >>> >>> We can safely move arch_check_zapped_pte() + tlb_remove_tlb_entry() + >>> zap_install_uffd_wp_if_needed() after updating the folio and RSS. >>> >>> While at it, only call zap_install_uffd_wp_if_needed() if there is even >>> any chance that pte_install_uffd_wp_if_needed() would do *something*. >>> That is, just don't bother if uffd-wp does not apply. >>> >>> Signed-off-by: David Hildenbrand >>> --- >>>   mm/memory.c | 16 +++++++++++----- >>>   1 file changed, 11 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 69502cdc0a7d..20bc13ab8db2 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -1552,12 +1552,9 @@ static inline void zap_present_pte(struct mmu_gather >>> *tlb, >>>       folio = page_folio(page); >>>       if (unlikely(!should_zap_folio(details, folio))) >>>           return; >>> -    ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); >>> -    arch_check_zapped_pte(vma, ptent); >>> -    tlb_remove_tlb_entry(tlb, pte, addr); >>> -    zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent); >>>         if (!folio_test_anon(folio)) { >>> +        ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); >>>           if (pte_dirty(ptent)) { >>>               folio_mark_dirty(folio); >>>               if (tlb_delay_rmap(tlb)) { >>> @@ -1567,8 +1564,17 @@ static inline void zap_present_pte(struct mmu_gather >>> *tlb, >>>           } >>>           if (pte_young(ptent) && likely(vma_has_recency(vma))) >>>               folio_mark_accessed(folio); >>> +        rss[mm_counter(folio)]--; >>> +    } else { >>> +        /* We don't need up-to-date accessed/dirty bits. */ >>> +        ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); >>> +        rss[MM_ANONPAGES]--; >>>       } >>> -    rss[mm_counter(folio)]--; >>> +    arch_check_zapped_pte(vma, ptent); >> >> Isn't the x86 (only) implementation of this relying on the dirty bit? So doesn't >> that imply you still need get_and_clear for anon? (And in hindsight I think that >> logic would apply to the previous patch too?) > > x86 uses the encoding !writable && dirty to indicate special shadow stacks. That > is, the hw dirty bit is set by software (to create that combination), not by > hardware. > > So you don't have to sync against any hw changes of the hw dirty bit. What you > had in the original PTE you read is sufficient. > Right, got it. In that case: Reviewed-by: Ryan Roberts