From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 244732FB0BD for ; Mon, 24 Nov 2025 10:27:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763980024; cv=none; b=aFNT3SyIO+iuk/OocfreqQr/aMzfRAsKhvnXpwq0w85W0wnOOywC8FolFP4cxEe/Azga4XSt3oXZzxS54MC46Lp0pg/16mueNjsiXzy5kET3SXdeAdky4cKfUIWWEs+HYF9k3deARi0qS+BVBdZy2W2iEFOjdmquYYRKeULqRpU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763980024; c=relaxed/simple; bh=Cw/QN7149lkWKCoCGFt6hcJE5ihImjpJqd3DyabjBzM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TrEr19xPoBI5DDEqXuR1xy1mz1l3qvh1/cRWHzGYpllq9HX/J+NEU8XEfDWjIG//hrjXF8hFHCNcISQud2OJEU/ApB+65JNiICP9SshyOhrY6WzbSbtO0rbzITENx9TD/2HEdt0QpJgJaHh8/aS9muwfqLwe1sNqSznGEClbmEY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pW6a1ge/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pW6a1ge/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AA1CC116D0; Mon, 24 Nov 2025 10:26:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763980023; bh=Cw/QN7149lkWKCoCGFt6hcJE5ihImjpJqd3DyabjBzM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 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 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 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