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Wed, 1 Jul 2020 08:29:15 +0000 (UTC) Received: from [10.36.112.52] (ovpn-112-52.ams2.redhat.com [10.36.112.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id A2E2D2B5BF; Wed, 1 Jul 2020 08:29:09 +0000 (UTC) Subject: Re: [PATCH] mm: define pte_add_end for consistency To: Wei Yang Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, akpm@linux-foundation.org, x86@kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org References: <20200630031852.45383-1-richard.weiyang@linux.alibaba.com> <40362e99-a354-c44f-8645-e2326a6df680@redhat.com> <20200701021113.GA51306@L-31X9LVDL-1304.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Wed, 1 Jul 2020 10:29:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200701021113.GA51306@L-31X9LVDL-1304.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.07.20 04:11, Wei Yang wrote: > On Tue, Jun 30, 2020 at 02:44:00PM +0200, David Hildenbrand wrote: >> On 30.06.20 05:18, Wei Yang wrote: >>> When walking page tables, we define several helpers to get the address of >>> the next boundary. But we don't have one for pte level. >>> >>> Let's define it and consolidate the code in several places. >>> >>> Signed-off-by: Wei Yang >>> --- >>> arch/x86/mm/init_64.c | 6 ++---- >>> include/linux/pgtable.h | 7 +++++++ >>> mm/kasan/init.c | 4 +--- >>> 3 files changed, 10 insertions(+), 7 deletions(-) >>> >>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c >>> index dbae185511cd..f902fbd17f27 100644 >>> --- a/arch/x86/mm/init_64.c >>> +++ b/arch/x86/mm/init_64.c >>> @@ -973,9 +973,7 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end, >>> >>> pte = pte_start + pte_index(addr); >>> for (; addr < end; addr = next, pte++) { >>> - next = (addr + PAGE_SIZE) & PAGE_MASK; >>> - if (next > end) >>> - next = end; >>> + next = pte_addr_end(addr, end); >>> >>> if (!pte_present(*pte)) >>> continue; >>> @@ -1558,7 +1556,7 @@ void register_page_bootmem_memmap(unsigned long section_nr, >>> get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO); >>> >>> if (!boot_cpu_has(X86_FEATURE_PSE)) { >>> - next = (addr + PAGE_SIZE) & PAGE_MASK; >>> + next = pte_addr_end(addr, end); >>> pmd = pmd_offset(pud, addr); >>> if (pmd_none(*pmd)) >>> continue; >>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>> index 32b6c52d41b9..0de09c6c89d2 100644 >>> --- a/include/linux/pgtable.h >>> +++ b/include/linux/pgtable.h >>> @@ -706,6 +706,13 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot) >>> }) >>> #endif >>> >>> +#ifndef pte_addr_end >>> +#define pte_addr_end(addr, end) \ >>> +({ unsigned long __boundary = ((addr) + PAGE_SIZE) & PAGE_MASK; \ >>> + (__boundary - 1 < (end) - 1) ? __boundary : (end); \ >>> +}) >>> +#endif >>> + >>> /* >>> * When walking page tables, we usually want to skip any p?d_none entries; >>> * and any p?d_bad entries - reporting the error before resetting to none. >>> diff --git a/mm/kasan/init.c b/mm/kasan/init.c >>> index fe6be0be1f76..89f748601f74 100644 >>> --- a/mm/kasan/init.c >>> +++ b/mm/kasan/init.c >>> @@ -349,9 +349,7 @@ static void kasan_remove_pte_table(pte_t *pte, unsigned long addr, >>> unsigned long next; >>> >>> for (; addr < end; addr = next, pte++) { >>> - next = (addr + PAGE_SIZE) & PAGE_MASK; >>> - if (next > end) >>> - next = end; >>> + next = pte_addr_end(addr, end); >>> >>> if (!pte_present(*pte)) >>> continue; >>> >> >> I'm not really a friend of this I have to say. We're simply iterating >> over single pages, not much magic .... > > Hmm... yes, we are iterating on Page boundary, while we many have the case > when addr or end is not PAGE_ALIGN. I really do wonder if not having page aligned addresses actually happens in real life. Page tables operate on page granularity, and adding/removing unaligned parts feels wrong ... and that's also why I dislike such a helper. 1. kasan_add_zero_shadow()/kasan_remove_zero_shadow(). If I understand the logic (WARN_ON()) correctly, we bail out in case we would ever end up in such a scenario, where we would want to add/remove things not aligned to PAGE_SIZE. 2. remove_pagetable()...->remove_pte_table() vmemmap_free() should never try to de-populate sub-pages. Even with sub-section hot-add/remove (2MB / 512 pages), with valid struct page sizes (56, 64, 72, 80), we always end up with full pages. kernel_physical_mapping_remove() is only called via arch_remove_memory(). That will never remove unaligned parts. 3. register_page_bootmem_memmap() It operates on full pages only. This needs in-depth analysis, but my gut feeling is that this alignment is unnecessary. > >> >> What would definitely make sense is replacing (addr + PAGE_SIZE) & >> PAGE_MASK; by PAGE_ALIGN() ... >> > > No, PAGE_ALIGN() is expanded to be > > (addr + PAGE_SIZE - 1) & PAGE_MASK; > > If we change the code to PAGE_ALIGN(), we would end up with infinite loop. Very right, it would have to be PAGE_ALIGN(addr + 1). -- Thanks, David / dhildenb