From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A5C0FD1A639 for ; Fri, 9 Jan 2026 15:04:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 178936B0089; Fri, 9 Jan 2026 10:04:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 125C96B008A; Fri, 9 Jan 2026 10:04:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0287E6B008C; Fri, 9 Jan 2026 10:04:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id EABD86B0089 for ; Fri, 9 Jan 2026 10:04:00 -0500 (EST) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id BA5F216010F for ; Fri, 9 Jan 2026 15:04:00 +0000 (UTC) X-FDA: 84312745440.17.88176BB Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf13.hostedemail.com (Postfix) with ESMTP id 1061320010 for ; Fri, 9 Jan 2026 15:03:58 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Uu2xDZmK; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767971039; a=rsa-sha256; cv=none; b=bWwP61leGJm9Bnjnjuhxt09AccMnFBGtqtM4FdVWS/OmW/GcxAbXsOoOH0D+fBTADNQEWW gYyorlunsDEiRaOeHrIGoSr44U4iT2ydv10vOoGX66jbJVAzspA7UGoeqgO2TO1wP49Mq/ EnSmh9aRQx6CjTeOz10NOA8K1hDot94= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Uu2xDZmK; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767971039; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=H6ssEdcHkr4lhwyK2u97S+QH0RFj6bQRJ9iwKKkYmk8=; b=dUhAtYHZlqFQAywO6dxTM86sIw9sbS2ssV7eRHpm/i28c5OVvoxXWAoOORGP0wJ6ayPXxJ A4AQSKFDl6AeupDPlpC/vXW/8k4yAYWSf/Z+RhnY1BALMCbEqEEbz5tuWSQTy3QMCqN8z+ 1TmZvz8n+bcO1VfTjKOjS8pxcqOXbac= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 1F23D41AAF; Fri, 9 Jan 2026 15:03:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B859DC4CEF1; Fri, 9 Jan 2026 15:03:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767971038; bh=9LFMVxyFsOw43Q6k6Eff0i7Pwixa+RzRx4DsbI5AqD4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Uu2xDZmK3PKrblsrsZL8LIcmnB0lca1ztGkSrwKnR3k1T+w3GGUw72vEWmRnJLC84 04PN8WJ3tZU0qJxzKPXK/jIY9eHM/FkWJFfqFlKmAMwFCu8bAOMnLGGisVhDa+VPC1 Hkm58qx6FwRjuIwh2iTdkxqN5OiOQDU6WIuS4LlqAy4eDc3QabNZxuLBa/iS/+tV6V fS5P07RUWs0rl3AKweG2OOOgL7ak053o/aoA2ECEjLInVqvpv88XZvchTU2IlUt4fg Y4VqP9kXVaCjmME3a4NjLke27874qGSfQHgAkzTpVnrAxfNYoR24aDyxZOKRFuYlCS Zo9TfPAXHUzMg== Message-ID: <0c72913e-9708-4675-a421-06ed82b7802a@kernel.org> Date: Fri, 9 Jan 2026 16:03:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 05/14] mm: clarify lazy_mmu sleeping constraints To: Kevin Brodsky , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Anshuman Khandual , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , David Woodhouse , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , "Ritesh Harjani (IBM)" , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Venkat Rao Bagalkote , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251215150323.2218608-1-kevin.brodsky@arm.com> <20251215150323.2218608-6-kevin.brodsky@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: <20251215150323.2218608-6-kevin.brodsky@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: q6b5mz8tnnyrua48y6nfdyp1c4fsdbnn X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1061320010 X-HE-Tag: 1767971038-957570 X-HE-Meta: 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 K3G1H/Vz YqI0NHQLnEXHuy1KlZ5SCn5zzWeuorlUQB4PMl6dMUvafWpQ= 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 12/15/25 16:03, Kevin Brodsky wrote: > The lazy MMU mode documentation makes clear that an implementation > should not assume that preemption is disabled or any lock is held > upon entry to the mode; however it says nothing about what code > using the lazy MMU interface should expect. > > In practice sleeping is forbidden (for generic code) while the lazy > MMU mode is active: say it explicitly. > > Signed-off-by: Kevin Brodsky > --- > include/linux/pgtable.h | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 652f287c1ef6..1abc4a1c3d72 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -225,11 +225,15 @@ static inline int pmd_dirty(pmd_t pmd) > * up to date. > * > * In the general case, no lock is guaranteed to be held between entry and exit > - * of the lazy mode. So the implementation must assume preemption may be enabled > - * and cpu migration is possible; it must take steps to be robust against this. > - * (In practice, for user PTE updates, the appropriate page table lock(s) are > - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted > - * and the mode cannot be used in interrupt context. > + * of the lazy mode. (In practice, for user PTE updates, the appropriate page > + * table lock(s) are held, but for kernel PTE updates, no lock is held). > + * The implementation must therefore assume preemption may be enabled upon > + * entry to the mode and cpu migration is possible; it must take steps to be > + * robust against this. An implementation may handle this by disabling > + * preemption, as a consequence generic code may not sleep while the lazy MMU > + * mode is active. > + * > + * Nesting is not permitted and the mode cannot be used in interrupt context. > */ > #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE > static inline void arch_enter_lazy_mmu_mode(void) {} Acked-by: David Hildenbrand (Red Hat) -- Cheers David