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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fab5250ddsm58327435e9.6.2025.10.10.06.03.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Oct 2025 06:03:37 -0700 (PDT) Message-ID: <5a98e3a4-287b-414f-801a-8054ece14662@redhat.com> Date: Fri, 10 Oct 2025 15:03:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 10/16] mm: define clear_pages(), clear_user_pages() From: David Hildenbrand 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: <20250917152418.4077386-1-ankur.a.arora@oracle.com> <20250917152418.4077386-11-ankur.a.arora@oracle.com> <5ec85b0b-9848-4cee-98f4-37953d504773@redhat.com> <87y0q4ewzf.fsf@oracle.com> <6743ead5-4d61-4274-a24f-13a8a8265aee@redhat.com> <87frcbayt2.fsf@oracle.com> <1b4e3a1a-eeff-4d48-9b1b-d20af1d94be2@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6F195A002B X-Stat-Signature: 8f3dgngw5gmdbqfmhm3tem6kn356i848 X-HE-Tag: 1760101424-8585 X-HE-Meta: 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 Pli8MO8n c1XUrGDFkvLbfIbEDWo70502FIYeeJ7BsHqgMS15LzVTZhU7q47VRQB0/WgHQITn3t1eSQbgrVHySQp1XaCHGhO8fUvGcfpUPhwsnBVkfm3Vj8BtLiw2tCSEJe9S1U7CQCr7GftNbg3rSxnTCDBKolyzakO87RWHSv1lzeoIPHWP3aoYz7rFAN+VrLNL/9HJlePUzdSNl2Uc75Vc= 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 10.10.25 12:37, David Hildenbrand wrote: > On 25.09.25 07:25, Ankur Arora wrote: >> >> David Hildenbrand writes: >> >>> On 23.09.25 22:26, Ankur Arora wrote: >>>> David Hildenbrand writes: >>>> >>>>> On 17.09.25 17:24, Ankur Arora wrote: >>>>>> Define fallback versions of clear_pages(), clear_user_pages(). >>>>>> In absence of architectural primitives, we just clear pages >>>>>> sequentially. >>>>>> Signed-off-by: Ankur Arora >>>>>> --- >>>>>> include/linux/mm.h | 38 ++++++++++++++++++++++++++++++++++++++ >>>>>> 1 file changed, 38 insertions(+) >>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>>>> index 1ae97a0b8ec7..0cde9b01da5e 100644 >>>>>> --- a/include/linux/mm.h >>>>>> +++ b/include/linux/mm.h >>>>>> @@ -3768,6 +3768,44 @@ static inline void clear_page_guard(struct zone *zone, struct page *page, >>>>>> unsigned int order) {} >>>>>> #endif /* CONFIG_DEBUG_PAGEALLOC */ >>>>>> +#ifndef clear_pages >>>>>> +/** >>>>>> + * clear_pages() - clear a page range using a kernel virtual address. >>>>> >>>>> I'd just call this "clear a page range for kernel-internal use" >>>>> >>>>>> + * @addr: start address >>>>>> + * @npages: number of pages >>>>>> + * >>>>>> + * Assumes that (@addr, +@npages) references a kernel region. >>>>> >>>>> And say here simply that "Use clear_user_pages() instead for clearing a page >>>>> range to be mapped to user space". >>>> So, comments that actually speak to the use instead of technically >>>> correct but unhelpful generalities :). Thanks, good lesson. >>>> >>>>>> + * Does absolutely no exception handling. >>>>>> + */ >>>>>> +static inline void clear_pages(void *addr, unsigned int npages) >>>>>> +{ >>>>>> + do { >>>>>> + clear_page(addr); >>>>>> + addr += PAGE_SIZE; >>>>>> + } while (--npages); >>>>>> +} >>>>>> +#endif >>>>>> + >>>>>> +#ifndef clear_user_pages >>>>>> +/** >>>>>> + * clear_user_pages() - clear a page range mapped by the user. >>>>> >>>>> I'd call this then "clear a page range to be mapped to user space" >>>>> >>>>> Because it's usually called before we actually map it and it will properly flush >>>>> the dcache if required. >>>> Makes sense. >>>> >>>>>> + * @addr: kernel mapped address >>>>> >>>>> "start address" >>>>> >>>>>> + * @vaddr: user mapped address >>>>> >>>>> "start address of the user mapping" ? >>>>> >>>>>> + * @pg: start page >>>>> >>>>> Please just call it "page". I know, clear_user_page() has this weird page vs. pg >>>>> thingy, but let's do it better here. >>>>> >>>>>> + * @npages: number of pages >>>>>> + * >>>>>> + * Assumes that the region (@addr, +@npages) has been validated >>>>>> + * already so this does no exception handling. >>>>>> + */ >>>>>> +#define clear_user_pages(addr, vaddr, pg, npages) \ >>>>>> +do { \ >>>>>> + clear_user_page(addr, vaddr, pg); \ >>>>>> + addr += PAGE_SIZE; \ >>>>>> + vaddr += PAGE_SIZE; \ >>>>>> + pg++; \ >>>>>> +} while (--npages) >>>>>> +#endif >>>>> >>>>> Should indent with one tab. >>>> Will do. Also acking to the ones above. >>>> >>>>> Any reason this is not a static inline function? >>>> Alas yes. Most architecture code defines clear_user_page() as a macro >>>> where, if they need a to flush the dcache or otherwise do something >>>> special, they need access to some external primitive. And this primitive >>>> which might not be visible in contexts that we include this header. >>>> For instance this one on sparc: >>>> https://lore.kernel.org/lkml/202509030338.DlQJTxIk-lkp@intel.com/ >>>> Defining as a macro to get around that. But maybe there's a better >>>> way? >>> >>> Can we just move it to mm/utils.c and not have it be an inline function? >> >> Thanks. Yeah, that's a good place for it. > > So, I'm looking into this and I think we should fixup the arch if possible. > > I now have > > commit 0f90e18abec6b6080af9ee5583cbba28d483a87d (HEAD) > Author: David Hildenbrand > Date: Fri Oct 10 06:09:51 2025 -0400 > > treewide: provide a generic clear_user_page() variant > > Let's drop all variants that effectively map to clear_page() and > provide it in a generic variant instead. > > We'll use __HAVE_ARCH_CLEAR_USER_PAGE, similar to > __HAVE_ARCH_COPY_USER_HIGHPAGE, to indicate whether an architecture > provides it's own variant. > > Maybe at some point these should be CONFIG_ options. > > Signed-off-by: David Hildenbrand > > > To get started. Did you only run into the issue with sparc or was there > another one problematic? > Okay, m68k is nasty as well. Change of plans, let's keep a clear_user_pages() variant in mm/utils.c when the arch has special clear_user_page() needs. -- Cheers David / dhildenb