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(p200300d82f1d01004f8ebb13c3c7f854.dip0.t-ipconnect.de. [2003:d8:2f1d:100:4f8e:bb13:c3c7:f854]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b6f0d32a2sm134907275e9.9.2025.08.29.07.34.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 Aug 2025 07:34:56 -0700 (PDT) Message-ID: <62fad23f-e8dc-4fd5-a82f-6419376465b5@redhat.com> Date: Fri, 29 Aug 2025 16:34:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 21/36] mm/cma: refuse handing out non-contiguous page ranges To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, Alexandru Elisei , 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, 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 References: <20250827220141.262669-1-david@redhat.com> <20250827220141.262669-22-david@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: DBH6iNE5BV1KmV1YVUwWeMGPsXHFPOxqjin9P_aAK28_1756478098 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 41B0E8000C X-Stat-Signature: df17p1da8k7kwyhky46877fx5xo9dwsk X-HE-Tag: 1756478101-426716 X-HE-Meta: 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 hFZ6YSQk 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 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 28.08.25 19:28, Lorenzo Stoakes wrote: > On Thu, Aug 28, 2025 at 12:01:25AM +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. > > I'm guessing this is something that we don't need to worry about in > reality? That my theory yes. > >> >> 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. >> >> Reviewed-by: Alexandru Elisei >> Signed-off-by: David Hildenbrand > > LGTM other than refactoring point below. > > CMA stuff looks fine afaict after staring at it for a while, on proviso > that handing out ranges within the same section is always going to be the > case. > > Anyway overall, > > LGTM, so: > > Reviewed-by: Lorenzo Stoakes > > >> --- >> include/linux/mm.h | 6 ++++++ >> mm/cma.c | 39 ++++++++++++++++++++++++--------------- >> mm/util.c | 33 +++++++++++++++++++++++++++++++++ >> 3 files changed, 63 insertions(+), 15 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index f6880e3225c5c..2ca1eb2db63ec 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 e56ec64d0567e..813e6dc7b0954 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 +835,24 @@ 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), >> - count, align); >> - /* try again with a bit different memory target */ >> - start = bitmap_no + mask + 1; >> + trace_cma_alloc_busy_retry(cma->name, pfn, page, count, align); >> } >> out: >> - *pagep = page; >> + if (!ret) >> + *pagep = page; >> return ret; >> } >> >> @@ -882,7 +891,7 @@ 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); >> } >> >> 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; > > I find this pretty confusing, my test for this is how many times I have to read > the code to understand what it's doing :) > > So we have something like: > > (pfn of page) > start_pfn pfn = align UP > | | > v v > | section | > <-----------------> > pfn - start_pfn > > Then check page + (pfn - start_pfn) == pfn_to_page(pfn) > > And loop such that: > > (pfn of page) > start_pfn pfn > | | > v v > | section | section | > <------------------------------------------> > pfn - start_pfn > > Again check page + (pfn - start_pfn) == pfn_to_page(pfn) > > And so on. > > So the logic looks good, but it's just... that took me a hot second to > parse :) > > I think a few simple fixups > > 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; > /* The PFN of the start of the next section. */ > unsigned long pfn = ALIGN(start_pfn, PAGES_PER_SECTION); > /* The page we'd expected to see if the range were contiguous. */ > struct page *expected = page + (pfn - start_pfn); > > /* > * The memmap is allocated per memory section. We need to check > * each involved memory section once. > */ > for (; pfn < end_pfn; pfn += PAGES_PER_SECTION, expected += PAGES_PER_SECTION) > if (unlikely(expected != pfn_to_page(pfn))) > return false; > return true; > } > Hm, I prefer my variant, especially where the pfn is calculated in the for loop. Likely a matter of personal taste. But I can see why skipping the first section might be a surprise when not having the semantics of ALIGN() in the cache. So I'll add the following on top: diff --git a/mm/util.c b/mm/util.c index 0bf349b19b652..fbdb73aaf35fe 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1303,8 +1303,10 @@ bool page_range_contiguous(const struct page *page, unsigned long nr_pages) unsigned long pfn; /* - * The memmap is allocated per memory section. We need to check - * each involved memory section once. + * The memmap is allocated per memory section, so no need to check + * within the first section. However, we need to check each other + * spanned memory section once, making sure the first page in a + * section could similarly be reached by just iterating pages. */ for (pfn = ALIGN(start_pfn, PAGES_PER_SECTION); pfn < end_pfn; pfn += PAGES_PER_SECTION) Thanks! -- Cheers David / dhildenb