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Wed, 01 Jul 2020 04:29:17 -0400 X-MC-Unique: X6NjWalSOliMFEI7Q2laIg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6BA228015F4; 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; 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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 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Queue-Id: 0043E1003DAF6 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 Content-Transfer-Encoding: quoted-printable 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: 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 addres= s 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, >>> =20 >>> pte =3D pte_start + pte_index(addr); >>> for (; addr < end; addr =3D next, pte++) { >>> - next =3D (addr + PAGE_SIZE) & PAGE_MASK; >>> - if (next > end) >>> - next =3D end; >>> + next =3D pte_addr_end(addr, end); >>> =20 >>> 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); >>> =20 >>> if (!boot_cpu_has(X86_FEATURE_PSE)) { >>> - next =3D (addr + PAGE_SIZE) & PAGE_MASK; >>> + next =3D pte_addr_end(addr, end); >>> pmd =3D 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 ol= dprot, pgprot_t newprot) >>> }) >>> #endif >>> =20 >>> +#ifndef pte_addr_end >>> +#define pte_addr_end(addr, end) \ >>> +({ unsigned long __boundary =3D ((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 en= tries; >>> * 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, un= signed long addr, >>> unsigned long next; >>> =20 >>> for (; addr < end; addr =3D next, pte++) { >>> - next =3D (addr + PAGE_SIZE) & PAGE_MASK; >>> - if (next > end) >>> - next =3D end; >>> + next =3D pte_addr_end(addr, end); >>> =20 >>> 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 .... >=20 > Hmm... yes, we are iterating on Page boundary, while we many have the c= ase > 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. >=20 >> >> What would definitely make sense is replacing (addr + PAGE_SIZE) & >> PAGE_MASK; by PAGE_ALIGN() ... >> >=20 > No, PAGE_ALIGN() is expanded to be=20 >=20 > (addr + PAGE_SIZE - 1) & PAGE_MASK; >=20 > If we change the code to PAGE_ALIGN(), we would end up with infinite lo= op. Very right, it would have to be PAGE_ALIGN(addr + 1). --=20 Thanks, David / dhildenb