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b=pW6a1ge/2iJNiBwbLWAnBy7dB+z64UWvW/6WI+bGI+5m8Lvq7RPsUL9+rqjKW5OfP ZGRSwTWCO+dLoETToAo064G7cx48rQm3qkd62nyHJrZFV9IsOszth+ids3XYU9q9y/ OJmtPfNBrFIE/uG49bPv6quTnZDCXWW3XF5iDng/+twMNVOeqWdozny6kQK26wuoA1 XEL490Rrw/b5zwEpY5wQCQMWj2PzKTaTfDqsl+GGOjDvsJXT+1pFo/RB9Ysmv/WxRW k0wXY9/p0xHZyxsn9QK42AGbZWAL6E5n8r5n8eC6Z0/BYbB9+XxKlzXYjaYFt1sdH7 FOiaMsOFeRCiQ== Message-ID: Date: Mon, 24 Nov 2025 11:26:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 2/7] mm: introduce clear_pages() and clear_user_pages() To: "Christophe Leroy (CS GROUP)" , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Cc: 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, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com References: <20251121202352.494700-1-ankur.a.arora@oracle.com> <20251121202352.494700-3-ankur.a.arora@oracle.com> <10a90b15-3e26-451a-bebf-f7ad8ba67d1b@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <10a90b15-3e26-451a-bebf-f7ad8ba67d1b@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8E005160005 X-Stat-Signature: mtpkibn84bhnw6wnpbtmea1szt7jnwtc X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1763980024-267439 X-HE-Meta: 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 Xpq17Unn vvATLPl21m56hn8m943mmrQP0aoUd6NtDYhzTNrBMhCFG2HD5klw9P+f6Pc9g8jIe5lcHWTEQ6jgMg1NkRCw6cc7rDHJsRjvakdXQ2I7ui/y6fi5Swp1YCdf/Twr9BDWwOZ5C2+tTIwG7x3v1c5X0F/H4vwvkQMuqM7PLPD5XW2Kj2Em/h/8Yc/pBEfseYXouOlbM4KfnuKUFTZt4E6cKKlM/ixnYTgdFKYC0Up8cs309NSoOl9TRz9ZkfNhGe/tyhvd1QmgZ8JNyoe8Y/4juH+h4JnUBZLW+MR3W8PBDkksiemURfDphKtFKDA== 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: Replying here while I am already at it. >> +#ifndef clear_pages >> +/** >> + * clear_pages() - clear a page range for kernel-internal use. >> + * @addr: start address >> + * @npages: number of pages >> + * >> + * Use clear_user_pages() instead when clearing a page range to be >> + * mapped to user space. >> + * >> + * Does absolutely no exception handling. >> + */ >> +static inline void clear_pages(void *addr, unsigned int npages) >> +{ >> + do { >> + clear_page(addr); >> + addr += PAGE_SIZE; >> + } while (--npages); > > Why a 'do while' instead of a 'while' ? More efficient when we know that npages > 0. > > Are you certain that this function will never ever be called with a nul > npages ? That is the expectation here, yes. We should probably document that expectation. > >> +} >> +#endif >> + >> #ifndef clear_user_page >> /** >> * clear_user_page() - clear a page to be mapped to user space >> @@ -3901,6 +3921,27 @@ static inline void clear_user_page(void *addr, unsigned long vaddr, struct page >> } >> #endif >> >> +/** >> + * clear_user_pages() - clear a page range to be mapped to user space >> + * @addr: start address >> + * @vaddr: start address of the user mapping >> + * @page: start page >> + * @npages: number of pages >> + * >> + * Assumes that the region (@addr, +@npages) has been validated >> + * already so this does no exception handling. >> + */ >> +#ifdef clear_user_pages >> +void clear_user_pages(void *addr, unsigned long vaddr, >> + struct page *page, unsigned int npages); > > By doing this you forbid architectures to define it as a static inline, > is that wanted ? Note that this is not the intention. The intention is to either use a direct mapping to clear_pages(), or fallback to the variant in mm/util.c. The architecture is currently never expected to provide clear_user_pages(). Wondering if we can make that cleaner. I'm wondering if the dependency on highmem.h here in mm.h is rather the problem. How I hate this macro crap with arch overrides. > >> +#else >> +static inline void clear_user_pages(void *addr, unsigned long vaddr, >> + struct page *page, unsigned int npages) >> +{ >> + clear_pages(addr, npages); >> +} >> +#endif >> + >> #ifdef __HAVE_ARCH_GATE_AREA >> extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm); >> extern int in_gate_area_no_mm(unsigned long addr); >> diff --git a/mm/util.c b/mm/util.c >> index 8989d5767528..3c6cd44db1bd 100644 >> --- a/mm/util.c >> +++ b/mm/util.c >> @@ -1344,3 +1344,16 @@ bool page_range_contiguous(const struct page *page, unsigned long nr_pages) >> } >> EXPORT_SYMBOL(page_range_contiguous); >> #endif >> + >> +#ifdef clear_user_page >> +void clear_user_pages(void *addr, > > What happens if clear_user_page is defined but not clear_user_pages ? In > that case it seems like the definition in linux/mm.h will conflict. The generic mm.h variant will not set clear_user_page() and consequently we map directly to clear_pages(). -- Cheers David