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Thu, 02 Jul 2020 12:28:24 -0400 X-MC-Unique: UImTSbjUPxWwzxl1EfVJlg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BDD2180058A; Thu, 2 Jul 2020 16:28:22 +0000 (UTC) Received: from [10.36.114.38] (ovpn-114-38.ams2.redhat.com [10.36.114.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4CF9D7BEAC; Thu, 2 Jul 2020 16:28:20 +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> <20200701115441.GA4979@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: <20200701115441.GA4979@L-31X9LVDL-1304.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Rspamd-Queue-Id: 0F0FA18229818 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 13:54, Wei Yang wrote: > On Wed, Jul 01, 2020 at 10:29:08AM +0200, David Hildenbrand wrote: >> 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. >> > > I don't have a very clear mind now, while when you look into > remove_pte_table(), it has two cases based on alignment of addr and next. > > If we always remove a page, the second case won't happen? So, the code talks about that the second case can only happen for vmemmap, never for direct mappings. I don't see a way how this could ever happen with current page sizes, even with sub-section hotadd (2MB). Maybe that is a legacy leftover or was never relevant? Or I am missing something important, where we could have sub-4k-page vmemmap data. -- Thanks, David / dhildenb