From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 135D01F2BA1; Wed, 19 Feb 2025 08:46:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739954762; cv=none; b=BTxK2TTjUvplNezL7MJn4RoqRvGW4jZbrn3gvCUIlGZmUXAz59sWa5B3/NuMlX0V2qgQVghGfF4KWelCGTRjgmG5ZVO9ivhwEELbGsV7UER+nkUfLw0nouUNrJSf54qwcw28TLrLvv5ijThbfmB2zVw+ObQnoDp1nHRmwtAPNTk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739954762; c=relaxed/simple; bh=/YM69NyeXToXoYl863l8m7IiKZJ+g4qrds2ofWwdqjY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RmEf31y2ET93FCcs2M+JpEhL5Df/9tvHuti9ZwP9sRBsYYN0rLlAn5I79F9iXe5N7k79/ugleijl1yVeXnNVGNoFJxvXrC0OHZQooII4PHRWNiR+ZQd4wVCGQ/SXNCLBr8RHolTKHjsupS4xvnD1VKhJYRr2gapIYLwUOm29SKY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 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 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 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); > } >