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 EB77932C8B; Tue, 26 Aug 2025 10:46:09 +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=1756205172; cv=none; b=lVpRpw3XdbcxyhAIssUAeGT68p2NO2QaBX1pOtCDlQqRWe94K/sn0cobj7Aje7Gu2S6e/wv1qd/6kAC+50vYMSY6pnkHqoKDhlxeLbtOxlGQuY6RkegK9T8HM+ky9I0zXvkfjc3jQsdmlQ4tm9BLq03D3zy7D7t17GKHMlo+360= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756205172; c=relaxed/simple; bh=RlYaQIsXPj/hYp0IY2hzpcUql9s2CJOIs/Vq55SuaEg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dpxrCLdKufhXareDb3Vurb23Q14RmhzSBQHMZlnn3rWYiIGT7ffwO2HGosclr3zfH+S72E4e4IAKI1ATPilOCkeo1PJR+rDFtKuLm9PKqJqqhj9fzs6ugOYq++ktRobp+eFY/CJ9MVDDrB41/sf/a1pf4Q1Pgo+hJaErhPS/Otw= 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 0AD2A1A00; Tue, 26 Aug 2025 03:46:01 -0700 (PDT) Received: from raptor (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 93FC13F694; Tue, 26 Aug 2025 03:46:01 -0700 (PDT) Date: Tue, 26 Aug 2025 11:45:58 +0100 From: Alexandru Elisei To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Lorenzo Stoakes , Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan Subject: Re: [PATCH RFC 21/35] mm/cma: refuse handing out non-contiguous page ranges Message-ID: References: <20250821200701.1329277-1-david@redhat.com> <20250821200701.1329277-22-david@redhat.com> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250821200701.1329277-22-david@redhat.com> Hi David, On Thu, Aug 21, 2025 at 10:06:47PM +0200, David Hildenbrand wrote: > Let's disallow handing out PFN ranges with non-contiguous pages, so we > can remove the nth-page usage in __cma_alloc(), and so any callers don't > have to worry about that either when wanting to blindly iterate pages. > > This is really only a problem in configs with SPARSEMEM but without > SPARSEMEM_VMEMMAP, and only when we would cross memory sections in some > cases. > > Will this cause harm? Probably not, because it's mostly 32bit that does > not support SPARSEMEM_VMEMMAP. If this ever becomes a problem we could > look into allocating the memmap for the memory sections spanned by a > single CMA region in one go from memblock. > > Signed-off-by: David Hildenbrand > --- > include/linux/mm.h | 6 ++++++ > mm/cma.c | 36 +++++++++++++++++++++++------------- > mm/util.c | 33 +++++++++++++++++++++++++++++++++ > 3 files changed, 62 insertions(+), 13 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ef360b72cb05c..f59ad1f9fc792 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -209,9 +209,15 @@ extern unsigned long sysctl_user_reserve_kbytes; > extern unsigned long sysctl_admin_reserve_kbytes; > > #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) > +bool page_range_contiguous(const struct page *page, unsigned long nr_pages); > #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n)) > #else > #define nth_page(page,n) ((page) + (n)) > +static inline bool page_range_contiguous(const struct page *page, > + unsigned long nr_pages) > +{ > + return true; > +} > #endif > > /* to align the pointer to the (next) page boundary */ > diff --git a/mm/cma.c b/mm/cma.c > index 2ffa4befb99ab..1119fa2830008 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -780,10 +780,8 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > unsigned long count, unsigned int align, > struct page **pagep, gfp_t gfp) > { > - unsigned long mask, offset; > - unsigned long pfn = -1; > - unsigned long start = 0; > unsigned long bitmap_maxno, bitmap_no, bitmap_count; > + unsigned long start, pfn, mask, offset; > int ret = -EBUSY; > struct page *page = NULL; > > @@ -795,7 +793,7 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > if (bitmap_count > bitmap_maxno) > goto out; > > - for (;;) { > + for (start = 0; ; start = bitmap_no + mask + 1) { > spin_lock_irq(&cma->lock); > /* > * If the request is larger than the available number > @@ -812,6 +810,22 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > spin_unlock_irq(&cma->lock); > break; > } > + > + pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit); > + page = pfn_to_page(pfn); > + > + /* > + * Do not hand out page ranges that are not contiguous, so > + * callers can just iterate the pages without having to worry > + * about these corner cases. > + */ > + if (!page_range_contiguous(page, count)) { > + spin_unlock_irq(&cma->lock); > + pr_warn_ratelimited("%s: %s: skipping incompatible area [0x%lx-0x%lx]", > + __func__, cma->name, pfn, pfn + count - 1); > + continue; > + } > + > bitmap_set(cmr->bitmap, bitmap_no, bitmap_count); > cma->available_count -= count; > /* > @@ -821,29 +835,25 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr, > */ > spin_unlock_irq(&cma->lock); > > - pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit); > mutex_lock(&cma->alloc_mutex); > ret = alloc_contig_range(pfn, pfn + count, ACR_FLAGS_CMA, gfp); > mutex_unlock(&cma->alloc_mutex); > - if (ret == 0) { > - page = pfn_to_page(pfn); > + if (!ret) > break; > - } > > cma_clear_bitmap(cma, cmr, pfn, count); > if (ret != -EBUSY) > break; > > pr_debug("%s(): memory range at pfn 0x%lx %p is busy, retrying\n", > - __func__, pfn, pfn_to_page(pfn)); > + __func__, pfn, page); > > trace_cma_alloc_busy_retry(cma->name, pfn, pfn_to_page(pfn), Nitpick: I think you already have the page here. > count, align); > - /* try again with a bit different memory target */ > - start = bitmap_no + mask + 1; > } > out: > - *pagep = page; > + if (!ret) > + *pagep = page; > return ret; > } > > @@ -882,7 +892,7 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count, > */ > if (page) { > for (i = 0; i < count; i++) > - page_kasan_tag_reset(nth_page(page, i)); > + page_kasan_tag_reset(page + i); Had a look at it, not very familiar with CMA, but the changes look equivalent to what was before. Not sure that's worth a Reviewed-by tag, but here it in case you want to add it: Reviewed-by: Alexandru Elisei Just so I can better understand the problem being fixed, I guess you can have two consecutive pfns with non-consecutive associated struct page if you have two adjacent memory sections spanning the same physical memory region, is that correct? Thanks, Alex > } > > if (ret && !(gfp & __GFP_NOWARN)) { > diff --git a/mm/util.c b/mm/util.c > index d235b74f7aff7..0bf349b19b652 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -1280,4 +1280,37 @@ unsigned int folio_pte_batch(struct folio *folio, pte_t *ptep, pte_t pte, > { > return folio_pte_batch_flags(folio, NULL, ptep, &pte, max_nr, 0); > } > + > +#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) > +/** > + * page_range_contiguous - test whether the page range is contiguous > + * @page: the start of the page range. > + * @nr_pages: the number of pages in the range. > + * > + * Test whether the page range is contiguous, such that they can be iterated > + * naively, corresponding to iterating a contiguous PFN range. > + * > + * This function should primarily only be used for debug checks, or when > + * working with page ranges that are not naturally contiguous (e.g., pages > + * within a folio are). > + * > + * Returns true if contiguous, otherwise false. > + */ > +bool page_range_contiguous(const struct page *page, unsigned long nr_pages) > +{ > + const unsigned long start_pfn = page_to_pfn(page); > + const unsigned long end_pfn = start_pfn + nr_pages; > + unsigned long pfn; > + > + /* > + * The memmap is allocated per memory section. We need to check > + * each involved memory section once. > + */ > + for (pfn = ALIGN(start_pfn, PAGES_PER_SECTION); > + pfn < end_pfn; pfn += PAGES_PER_SECTION) > + if (unlikely(page + (pfn - start_pfn) != pfn_to_page(pfn))) > + return false; > + return true; > +} > +#endif > #endif /* CONFIG_MMU */ > -- > 2.50.1 > >