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[2003:d8:2f0a:2e00:89cb:c7f0:82f2:e43c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454dd537932sm55615205e9.20.2025.07.11.12.27.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Jul 2025 12:27:30 -0700 (PDT) Message-ID: <4253b58b-374d-40b4-87d8-f66926d65676@redhat.com> Date: Fri, 11 Jul 2025 21:27:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 10/14] x86/mm: Simplify clear_page_* To: Ankur Arora Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, mjguzik@gmail.com, luto@kernel.org, peterz@infradead.org, acme@kernel.org, namhyung@kernel.org, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com References: <20250710005926.1159009-1-ankur.a.arora@oracle.com> <20250710005926.1159009-11-ankur.a.arora@oracle.com> <377d74d6-a7f9-4e94-9276-168a26d49210@redhat.com> <874iviprkf.fsf@oracle.com> <87tt3imsxn.fsf@oracle.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6854120002 X-Stat-Signature: 1sjy1m48tanpgihxqsura1jkac7ux31a X-Rspam-User: X-HE-Tag: 1752262057-136154 X-HE-Meta: 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 cLVxvCvY 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 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 11.07.25 21:24, Ankur Arora wrote: > > David Hildenbrand writes: > >> On 11.07.25 19:26, Ankur Arora wrote: >>> David Hildenbrand writes: >>> >>>> On 10.07.25 02:59, Ankur Arora wrote: >>>>> clear_page_rep() and clear_page_erms() are wrappers around "REP; STOS" >>>>> variations. Inlining gets rid of an unnecessary CALL/RET (which isn't >>>>> free when using RETHUNK speculative execution mitigations.) >>>>> Fixup and rename clear_page_orig() to adapt to the changed calling >>>>> convention. >>>>> And, add a comment from Dave Hansen detailing various clearing mechanisms >>>>> used in clear_page(). >>>>> Signed-off-by: Ankur Arora >>>>> --- >>>>> arch/x86/include/asm/page_32.h | 6 +++++ >>>>> arch/x86/include/asm/page_64.h | 42 ++++++++++++++++++++++++++-------- >>>>> arch/x86/lib/clear_page_64.S | 39 +++++++------------------------ >>>>> 3 files changed, 46 insertions(+), 41 deletions(-) >>>>> diff --git a/arch/x86/include/asm/page_32.h b/arch/x86/include/asm/page_32.h >>>>> index 0c623706cb7e..a8ff43bb9652 100644 >>>>> --- a/arch/x86/include/asm/page_32.h >>>>> +++ b/arch/x86/include/asm/page_32.h >>>>> @@ -17,6 +17,12 @@ extern unsigned long __phys_addr(unsigned long); >>>>> #include >>>>> +/* >>>> >>>> /** if this was supposed to be kernel doc (which it looks like it is) >>>> >>>>> + * clear_page() - clear kernel page. >>>> >>>> "clear a kernel page" >>>> >>>> Although I am not sure what a "kernel page" is. >>>> >>>> Did you mean "clear a page using a kernel virtual address" ? >>> Thanks. Yes, this makes way more sense. >> >> FWIW, most clear_user_page() will just call clear_page(). The ones that don't, >> have to deal with the dcache flushing, as the page might have cache alias from >> another (mm) address space. >> >> So clear_page() is just about clearing page content using a kernel virtual >> address, and clear_user_page() is additionally taking care of any dcache >> aliases. > > Yeah that's a good point. > > Right now I'm assuming that clear_user_page() and clear_page() are > effectively identical. Which as you say, isn't true for all the > architectures that can't disambiguate dcache aliases. > > So maybe I should be adjusting the naming of the helpers a bit? > > Specifically, by calling clear_user_pages() from clear_pages_resched(). > Which on x86 etc can just call clear_pages(). Right, and calling it from folio_zero_user() :) -- Cheers, David / dhildenb