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Tue, 11 Feb 2020 09:01:40 -0500 X-MC-Unique: W9H-8s6-ONCkO4I7p0HkSA-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 B45FF1083835; Tue, 11 Feb 2020 14:01:38 +0000 (UTC) Received: from [10.36.117.14] (ovpn-117-14.ams2.redhat.com [10.36.117.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id DF82D90CFF; Tue, 11 Feb 2020 14:01:36 +0000 (UTC) Subject: Re: [Patch v2] mm/sparsemem: get address to page struct instead of address to pfn To: Wei Yang Cc: akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baoquan He References: <20200210005048.10437-1-richardw.yang@linux.intel.com> <90742479-cbb1-4ea9-c20c-53a1df34b806@redhat.com> <20200210231623.GC32495@richard> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200210231623.GC32495@richard> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 11.02.20 00:16, Wei Yang wrote: > On Mon, Feb 10, 2020 at 10:00:47AM +0100, David Hildenbrand wrote: >> On 10.02.20 01:50, Wei Yang wrote: >>> memmap should be the address to page struct instead of address to pfn. >>> >> >> "mm/sparsemem: fix wrong address in ms->section_mem_map with sub-sections >> >> We want to store the address of the memmap, not the address of the first >> pfn. >> >> E.g., we can have both (boot) system memory and devmem residing in a >> single section. Once we hot-add the devmem part, the address stored in >> ms->section_mem_map would be wrong, and kdump would not be able to >> dump the right memory. >> " >> >> ? See below >> >>> As mentioned by David, if system memory and devmem sit within a >>> section, the mismatch address would lead kdump to dump unexpected >>> memory. >>> >>> Since sub-section only works for SPARSEMEM_VMEMMAP, pfn_to_page() is >>> valid to get the page struct address at this point. >>> >>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") >>> Signed-off-by: Wei Yang >>> CC: Dan Williams >>> CC: David Hildenbrand >>> CC: Baoquan He >>> >>> --- >>> v2: >>> * adjust comment to mention the mismatch data would affect kdump >>> >>> --- >>> mm/sparse.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/sparse.c b/mm/sparse.c >>> index 586d85662978..4862ec2cfbc0 100644 >>> --- a/mm/sparse.c >>> +++ b/mm/sparse.c >>> @@ -887,7 +887,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, >>> >>> /* Align memmap to section boundary in the subsection case */ >>> if (section_nr_to_pfn(section_nr) != start_pfn) >>> - memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr)); >>> + memmap = pfn_to_page(section_nr_to_pfn(section_nr)); >> >> I think this whole code should be reworked. >> >> Callee returns a pointer. Caller: Nah, I know it better. >> >> Just nasty. >> >> >> Can we do something like this instead: >> >> >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c >> index 200aef686722..c5091feef29e 100644 >> --- a/mm/sparse-vmemmap.c >> +++ b/mm/sparse-vmemmap.c >> @@ -266,5 +266,5 @@ struct page * __meminit >> __populate_section_memmap(unsigned long pfn, >> if (vmemmap_populate(start, end, nid, altmap)) >> return NULL; >> >> - return pfn_to_page(pfn); >> + return pfn_to_page(SECTION_ALIGN_DOWN(pfn)); >> } >> diff --git a/mm/sparse.c b/mm/sparse.c >> index c184b69460b7..21902d7931e4 100644 >> --- a/mm/sparse.c >> +++ b/mm/sparse.c >> @@ -788,6 +788,10 @@ static void section_deactivate(unsigned long pfn, >> unsigned long nr_pages, >> depopulate_section_memmap(pfn, nr_pages, altmap); >> } >> >> +/* >> + * Returns the memmap of the first pfn of the section (not of >> + * sub-sections). >> + */ >> static struct page * __meminit section_activate(int nid, unsigned long pfn, >> unsigned long nr_pages, struct vmem_altmap *altmap) >> { >> @@ -882,9 +886,6 @@ int __meminit sparse_add_section(int nid, unsigned >> long start_pfn, >> set_section_nid(section_nr, nid); >> section_mark_present(ms); >> >> - /* Align memmap to section boundary in the subsection case */ >> - if (section_nr_to_pfn(section_nr) != start_pfn) >> - memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr)); >> sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0); >> >> return 0; >> >> >> Untested, of course :) > > I think you get some point. As you mentioned in the following reply, we need > to adjust poisoning after this change. We can just poison after setting up the section (IOW, move it further down). > > This looks like a trade off between two options. I don't have a strong > preference. I clearly prefer if *section*_activate() returns the memmap of the section. This code is just confusing. But I can send a cleanup on top if you want to keep it like that for now. -- Thanks, David / dhildenb