From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BE95C606A31A for ; Thu, 29 Oct 2026 14:31:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=S+7+kNzI Received: by kanga.kvack.org (Postfix) id D57316B05B1; Thu, 29 Oct 2026 10:31:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CE1AA6B05B9; Thu, 29 Oct 2026 10:31:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B81316B05BA; Thu, 29 Oct 2026 10:31:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 93CE46B05B1 for ; Thu, 29 Oct 2026 10:31:33 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 075B71C3B86 for ; Thu, 29 Oct 2026 14:31:33 +0000 (UTC) X-FDA: 85375902066.23.39EFFAE Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf06.hostedemail.com (Postfix) with ESMTP id EE9B618001A for ; Thu, 29 Oct 2026 14:31:30 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=S+7+kNzI; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793284291; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=mqXY1OcC5ARgzPi+R8XxHlz09YM9rQmQCBQ/7d/aXCU=; b=4spKq6eaa0vbDm6mqr7HnN7pAuh0DoSNvG148Cgw59tVrR/+5Wbd+vjIlxb5N8FdjWOjDq 2RStCD33OAvjmvG9iZJjb7YKzeR9Snl4w4lzsBeMN1q6cm3pYWiTYly8DQJiH3i3hvGMTr wTuPzV+I1x/Xxo5MxVPLwt6tq5qIoRE= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=S+7+kNzI; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793284291; b=d0X0WVOXk0FrNzXd/pQtzVIkr7VePnYh95oZrVIF/R5ZloHOsypFDJdyr0GRENvxIMpsqN aD2kZ8jMfTE7oiAyNK0QzkJfnTW4MYYaSiiuyL2RbIxkalFjdz45CqaKaRxvSzQFDzYu37 CtHzm1t40E2RNjS25aKmHK5ZHnH5OvI= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 34ED143CCB; Thu, 29 Oct 2026 14:31:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6CB091F01829; Thu, 29 Oct 2026 14:31:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793284290; bh=mqXY1OcC5ARgzPi+R8XxHlz09YM9rQmQCBQ/7d/aXCU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=S+7+kNzIX2ZMdfMr/hr6l4bhKncW3jvATRjUZNWSosKkVDp+gfFYQ4kqjyiXjyyAK gs5kPXW8xG/0KT+HvaTk4xQTZL9v3hHSNBHmZpL8Pp7wWOJucUIy6ZbUAV4KXBR9x1 WYtze+u+asK21+yj3mqxwfp+1brn7eF/wYYE4dYb/mAQp0dP7jvSdnFY4f35xAZv1W 1wJ5WknxozTNNR3uE3WCHiS9+iQbSjFlGEJv0CzUW305T8TDzosH2HSKrlhpFrYV0d IFR/sChwTcpkPvhDuq0AUrOOuXSZfwDloqRcMjT2PK3CjH1QEgeNOgtYdTI1xnrx0/ Ylgvn4jx6UkMQ== Received: from phl-compute-01.internal (phl-compute-01.internal [10.202.2.41]) by mailfauth.ams.internal (Postfix) with ESMTP id D7CDE198003A; Thu, 29 Oct 2026 10:31:14 -0400 (EDT) Received: from phl-frontend-04 ([10.202.2.163]) by phl-compute-01.internal (MEProxy); Thu, 29 Oct 2026 10:31:24 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTEZfGskmN/KIALm0CJB+7YSa6+/0z6TYSZsJYszNysoKl9ha19QRgLMFtDXR5YTJU /ZtSllXOANZXHyFMLUtTazs3TqL4wn789TDCt9Clg6UWb/6TcorYCgPnRO1yG/d+ASCNki ef8dq7SubLCazhJOigTaPhJlXCh+AauxneJX30NAaSC9cSSvOTgd/RYPeHFhgwmIxxm9Yd XUnA7opn8M6R0HNovJsW3EeF88ulEUJFLh9pAaky7aJDjYSiN5BtFPOV7TerL4btsXoEPq cp6ZV2vmAclzI+C8mBPXQk99548l2lhaunvBg1pEEnk0CURYD04FMA3h2gwijrqVLBamEX +KoxpWN36HbdMDBokyDgZcydhpS1f9KgI8PaFAed8ADm5abJnc6vuHwnggI8aO9IAtffDI ipCbDbz1M0bdaXw7zTOgeTBkOyOY6iObnEFXJnh8OiD+rhFLRxfOgjlS5bLqPRuXOEA7dc zuovqc0yO0PHGX5SV5M+OqtwEuHlLIRmba3XmtKAmvZQn97ay5w+2tiMYysvPf4WcLEm0y mClz5VTCDYXL6iInsVZEfxH8cbr6DpXm1B3a05NNC7Hkc4aI3diZhsPjvb2EocdX3sTJRy rSmOHFVblnqwyUxgB9IIfYCWAnZ7TnDQAP2A4F7kC+UwttipX8k4t0q/Ks7w X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 29 Oct 2026 10:31:11 -0400 (EDT) Date: Thu, 29 Oct 2026 14:31:10 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 42/46] mm/huge_memory: split huge PUDs when adjusting VMA boundaries Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-42-6f74bec9a5bb@kernel.org> <9f4128a4-85fc-4f4b-ac41-b9d348f56e37@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9f4128a4-85fc-4f4b-ac41-b9d348f56e37@kernel.org> X-Rspamd-Queue-Id: EE9B618001A X-Stat-Signature: hq1eapo6a6oohzyk8xcezkgbegsmrf9f X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793284290-892573 X-HE-Meta: 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 239+XhxD m43+kBh4aCIO7/dGpNivSzVFd5gbkBnb5aLGqYILSSDRtQYOO2fmjOlaZMkck35upiBUrthjPH4/cUC+p/f8XdYVTxHePFJHQ+4a3aG1qK1HNBZ8mqoaWv5I/q97CcvXmCLdql7sLKtovLgNST6Ff6ASXs6MFAHmQm8WAtZXuZeTHd44iEaxtUlYnhiAwVWsuURDwSnkCLI8jYRt6a56Z50apDn4OMUxxvOANLHlWfuNgyBg6lHByMIm1tT4uYg+wEfzv/LCU2jOm5ftc8+H+QisGBrT4DQMBmoke6vVd6MFuF5/IzY1Y0tmYN3Pe/XRIueFHa2R73wn89HnXK1vO6FOFwSeJafQlxg4e7GHA9WXx0QWsXUBDU8gUcIe1K0AC/NkND2JwH/3QKdeL6Z3a6u8M0KVNE38xlf6zpjpnZq1P887GJsMu6GKpDhPxAC0Gl441X7Bfz+RM7+sJQ+uMOoxTMw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Oct 29, 2026 at 03:24:29PM +0100, David Hildenbrand (Arm) wrote: > On 10/29/26 12:45, Kiryl Shutsemau wrote: > > On Tue, Oct 27, 2026 at 12:18:02AM +0100, David Hildenbrand (Arm) wrote: > >> PFN mappings such as VFIO PCI BAR mappings can use PUD leaves while > >> allowing VMA splits at page granularity. However, vma_adjust_trans_huge() > >> only handles PMDs. > >> > >> After faulting a writable PUD-sized VFIO BAR mapping, changing its first > >> page to read-only with mprotect() makes the PMD walk treat the PUD leaf > >> as a PMD table. Applying MADV_DONTFORK to the first PMD-sized chunk leaves > >> the PUD spanning two VMAs: the PMD-aligned boundary skips splitting. > >> > >> Walk the page tables once at each adjusted boundary and split a huge > >> PUD or PMD leaf as needed. Handle PUD leaves even when the boundary is > >> PMD-aligned. > >> > >> Fixes: f9e54c3a2f5b7 ("vfio/pci: implement huge_fault support") > >> Cc: stable@vger.kernel.org > >> Signed-off-by: David Hildenbrand (Arm) > >> --- > >> mm/huge_memory.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++-------- > >> 1 file changed, 60 insertions(+), 10 deletions(-) > >> > >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c > >> index 08e58cda7d37d..d090642ac8c2b 100644 > >> --- a/mm/huge_memory.c > >> +++ b/mm/huge_memory.c > >> @@ -3503,16 +3503,66 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > >> __split_huge_pmd(vma, pmd, address, freeze); > >> } > >> > >> -static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned long address) > >> +static bool pud_split_required(const struct vm_area_struct *vma, > >> + unsigned long address) > >> { > >> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)) > >> + return false; > >> + if (IS_ALIGNED(address, HPAGE_PUD_SIZE)) > >> + return false; > >> /* > >> - * If the new address isn't hpage aligned and it could previously > >> - * contain an hugepage: check if we need to split an huge pmd. > >> + * Only selected VMAs support mapping PUDs for now. Lift the > >> + * restriction once this changes. > >> */ > >> - if (!IS_ALIGNED(address, HPAGE_PMD_SIZE) && > >> - range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE), > >> - ALIGN(address, HPAGE_PMD_SIZE))) > >> - split_huge_pmd_address(vma, address, false); > >> + if (!vma_is_dax(vma) && !vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT)) > >> + return false; > >> + return range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PUD_SIZE), > >> + ALIGN(address, HPAGE_PUD_SIZE)); > >> +} > >> + > >> +static bool pmd_split_required(const struct vm_area_struct *vma, > >> + unsigned long address) > >> +{ > >> + if (IS_ALIGNED(address, HPAGE_PMD_SIZE)) > >> + return false; > >> + > >> + return range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE), > >> + ALIGN(address, HPAGE_PMD_SIZE)); > >> +} > >> + > >> +static void split_huge_leaf(struct vm_area_struct *vma, > >> + unsigned long address) > >> +{ > >> + const bool split_pud = pud_split_required(vma, address); > >> + const bool split_pmd = pmd_split_required(vma, address); > >> + pgd_t *pgd; > >> + p4d_t *p4d; > >> + pud_t *pud; > >> + pmd_t *pmd; > >> + > >> + /* > >> + * mmap, VMA and rmap write locks protect the walk; the split helpers > >> + * take the page table locks. > >> + */ > >> + if (!split_pud && !split_pmd) > >> + return; > >> + > >> + pgd = pgd_offset(vma->vm_mm, address); > >> + if (!pgd_present(*pgd)) > >> + return; > >> + > >> + p4d = p4d_offset(pgd, address); > >> + if (!p4d_present(*p4d)) > >> + return; > >> + > >> + pud = pud_offset(p4d, address); > >> + if (split_pud && pud_leaf(*pud)) > >> + __split_huge_pud(vma, pud, address); > >> + if (!split_pmd || !pud_present(*pud)) > >> + return; > > > > This looks wrong. > > > > We should bail out here if PUD is was a leaf and wasn't split. > > __split_huge_pud() must split a leave. Either by zapping it (what we do right > now) or by populating page tables (as in Usama's PoC). No, meant the situation when pud_leaf() is true, but split_pud is false, so __split_huge_pud() is never hit. pud_present() is true so we proceed to pmd_offset() -- Kiryl Shutsemau / Kirill A. Shutemov