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Tue, 12 Jan 2021 09:53:20 +0000 (UTC) Received: from [10.36.115.140] (ovpn-115-140.ams2.redhat.com [10.36.115.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6A09E77714; Tue, 12 Jan 2021 09:53:18 +0000 (UTC) Subject: Re: [PATCH v2 2/5] mm: Teach pfn_to_online_page() to consider subsection validity To: Dan Williams , linux-mm@kvack.org Cc: Qian Cai , Michal Hocko , vishal.l.verma@intel.com, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, Anshuman Khandual References: <161044407603.1482714.16630477578392768273.stgit@dwillia2-desk3.amr.corp.intel.com> <161044408728.1482714.9086710868634042303.stgit@dwillia2-desk3.amr.corp.intel.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <0586c562-787c-4872-4132-18a49c3ffc8e@redhat.com> Date: Tue, 12 Jan 2021 10:53:17 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <161044408728.1482714.9086710868634042303.stgit@dwillia2-desk3.amr.corp.intel.com> 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-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 12.01.21 10:34, Dan Williams wrote: > pfn_section_valid() determines pfn validity on subsection granularity. > > pfn_valid_within() internally uses pfn_section_valid(), but gates it > with early_section() to preserve the traditional behavior of pfn_valid() > before subsection support was added. > > pfn_to_online_page() wants the explicit precision that pfn_valid() does > not offer, so use pfn_section_valid() directly. Since > pfn_to_online_page() already open codes the validity of the section > number vs NR_MEM_SECTIONS, there's not much value to using > pfn_valid_within(), just use pfn_section_valid(). This loses the > valid_section() check that pfn_valid_within() was performing, but that > was already redundant with the online check. > > Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()") > Cc: Qian Cai > Cc: Michal Hocko > Reported-by: David Hildenbrand > --- > mm/memory_hotplug.c | 16 ++++++++++++---- > 1 file changed, 12 insertions(+), 4 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 55a69d4396e7..a845b3979bc0 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -308,11 +308,19 @@ static int check_hotplug_memory_addressable(unsigned long pfn, > struct page *pfn_to_online_page(unsigned long pfn) > { > unsigned long nr = pfn_to_section_nr(pfn); > + struct mem_section *ms; > + > + if (nr >= NR_MEM_SECTIONS) > + return NULL; > + > + ms = __nr_to_section(nr); > + if (!online_section(ms)) > + return NULL; > + > + if (!pfn_section_valid(ms, pfn)) > + return NULL; That's not sufficient for alternative implementations of pfn_valid(). You still need some kind of pfn_valid(pfn) for alternative versions of pfn_valid(). Consider arm64 memory holes in the memmap. See their current (yet to be fixed/reworked) pfn_valid() implementation. (pfn_valid_within() is implicitly active on arm64) Actually, I think we should add something like the following, to make this clearer (pfn_valid_within() is confusing) #ifdef CONFIG_HAVE_ARCH_PFN_VALID /* We might have to check for holes inside the memmap. */ if (!pfn_valid()) return NULL; #endif > > - if (nr < NR_MEM_SECTIONS && online_section_nr(nr) && > - pfn_valid_within(pfn)) > - return pfn_to_page(pfn); > - return NULL; > + return pfn_to_page(pfn); > } > EXPORT_SYMBOL_GPL(pfn_to_online_page); > > -- Thanks, David / dhildenb