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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 024D0C021AB for ; Wed, 19 Feb 2025 09:01:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=EJgtVuggDol4bUUoBoHdZtCxw6dhDYTxpOE1SY33YZQ=; b=u0fA5IKSvh49m+SQi/JXwGAyed QbTCR7hukOhSUsu21vmeK0Xrf3vMcmBabmKDSseK+4c8kW7PcMjnr6zP0ulzcIloyQo9Suha2wTau YfVONWdw1/5O8nhsUFJVyZqUKMMfo5bzuD/f2bXWQi4oB/1zesPm//o0DTw6DWTNwY+lt2Cdms5Ao QBeUG54+J98QiwpyMLxik/lJhrH9Igz46el0ePDjN9SkbdkLeq34StZ0bR4w+aIRVpLC7KTlUrRKZ DKD2yEnNxZkfOUSJNjSCljoercrhOWCEMhbZouACWYUMJeoTSB/LDNUUbCyAuP2QzLrDC9gKQYbB2 wqdhxX6Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tkfxO-0000000Bi3c-0UmQ; Wed, 19 Feb 2025 09:01:26 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tkfiS-0000000BcXO-3uCJ for linux-arm-kernel@lists.infradead.org; Wed, 19 Feb 2025 08:46:02 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BAC461682; Wed, 19 Feb 2025 00:46:18 -0800 (PST) Received: from [10.162.42.6] (unknown [10.162.42.6]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E695D3F5A1; Wed, 19 Feb 2025 00:45:47 -0800 (PST) Message-ID: Date: Wed, 19 Feb 2025 14:15:44 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] arm64: hugetlb: Fix huge_ptep_get_and_clear() for non-present ptes To: Ryan Roberts , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Gerald Schaefer , "David S. Miller" , Andreas Larsson , Arnd Bergmann , Muchun Song , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , David Hildenbrand , "Matthew Wilcox (Oracle)" , Mark Rutland , Dev Jain , Kevin Brodsky , Alexandre Ghiti Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250217140419.1702389-1-ryan.roberts@arm.com> <20250217140419.1702389-3-ryan.roberts@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20250217140419.1702389-3-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250219_004601_077667_941E17F9 X-CRM114-Status: GOOD ( 36.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2/17/25 19:34, Ryan Roberts wrote: > arm64 supports multiple huge_pte sizes. Some of the sizes are covered by > a single pte entry at a particular level (PMD_SIZE, PUD_SIZE), and some > are covered by multiple ptes at a particular level (CONT_PTE_SIZE, > CONT_PMD_SIZE). So the function has to figure out the size from the > huge_pte pointer. This was previously done by walking the pgtable to > determine the level and by using the PTE_CONT bit to determine the > number of ptes at the level. > > But the PTE_CONT bit is only valid when the pte is present. For > non-present pte values (e.g. markers, migration entries), the previous > implementation was therefore erroniously determining the size. There is > at least one known caller in core-mm, move_huge_pte(), which may call > huge_ptep_get_and_clear() for a non-present pte. So we must be robust to > this case. Additionally the "regular" ptep_get_and_clear() is robust to > being called for non-present ptes so it makes sense to follow the > behaviour. > > Fix this by using the new sz parameter which is now provided to the > function. Additionally when clearing each pte in a contig range, don't > gather the access and dirty bits if the pte is not present. > > An alternative approach that would not require API changes would be to > store the PTE_CONT bit in a spare bit in the swap entry pte for the > non-present case. But it felt cleaner to follow other APIs' lead and > just pass in the size. > > As an aside, PTE_CONT is bit 52, which corresponds to bit 40 in the swap > entry offset field (layout of non-present pte). Since hugetlb is never > swapped to disk, this field will only be populated for markers, which > always set this bit to 0 and hwpoison swap entries, which set the offset > field to a PFN; So it would only ever be 1 for a 52-bit PVA system where > memory in that high half was poisoned (I think!). So in practice, this > bit would almost always be zero for non-present ptes and we would only > clear the first entry if it was actually a contiguous block. That's > probably a less severe symptom than if it was always interpretted as 1 > and cleared out potentially-present neighboring PTEs. > > Cc: stable@vger.kernel.org > Fixes: 66b3923a1a0f ("arm64: hugetlb: add support for PTE contiguous bit") > Signed-off-by: Ryan Roberts > --- > arch/arm64/mm/hugetlbpage.c | 40 ++++++++++++++++--------------------- > 1 file changed, 17 insertions(+), 23 deletions(-) > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c > index 06db4649af91..614b2feddba2 100644 > --- a/arch/arm64/mm/hugetlbpage.c > +++ b/arch/arm64/mm/hugetlbpage.c > @@ -163,24 +163,23 @@ static pte_t get_clear_contig(struct mm_struct *mm, > unsigned long pgsize, > unsigned long ncontig) > { > - pte_t orig_pte = __ptep_get(ptep); > - unsigned long i; > - > - for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) { > - pte_t pte = __ptep_get_and_clear(mm, addr, ptep); > - > - /* > - * If HW_AFDBM is enabled, then the HW could turn on > - * the dirty or accessed bit for any page in the set, > - * so check them all. > - */ > - if (pte_dirty(pte)) > - orig_pte = pte_mkdirty(orig_pte); > - > - if (pte_young(pte)) > - orig_pte = pte_mkyoung(orig_pte); > + pte_t pte, tmp_pte; > + bool present; > + > + pte = __ptep_get_and_clear(mm, addr, ptep); > + present = pte_present(pte); pte_present() may not be evaluated for standard huge pages at [PMD|PUD]_SIZE e.g when ncontig = 1 in the argument. > + while (--ncontig) { Should this be converted into a for loop instead just to be in sync with other similar iterators in this file. for (i = 1; i < ncontig; i++, addr += pgsize, ptep++) { tmp_pte = __ptep_get_and_clear(mm, addr, ptep); if (present) { if (pte_dirty(tmp_pte)) pte = pte_mkdirty(pte); if (pte_young(tmp_pte)) pte = pte_mkyoung(pte); } } > + ptep++; > + addr += pgsize; > + tmp_pte = __ptep_get_and_clear(mm, addr, ptep); > + if (present) { > + if (pte_dirty(tmp_pte)) > + pte = pte_mkdirty(pte); > + if (pte_young(tmp_pte)) > + pte = pte_mkyoung(pte); > + } > } > - return orig_pte; > + return pte; > } > > static pte_t get_clear_contig_flush(struct mm_struct *mm, > @@ -401,13 +400,8 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr, > { > int ncontig; > size_t pgsize; > - pte_t orig_pte = __ptep_get(ptep); > - > - if (!pte_cont(orig_pte)) > - return __ptep_get_and_clear(mm, addr, ptep); > - > - ncontig = find_num_contig(mm, addr, ptep, &pgsize); > > + ncontig = num_contig_ptes(sz, &pgsize); > return get_clear_contig(mm, addr, ptep, pgsize, ncontig); > } >