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Fri, 5 Mar 2021 18:24:31 +0000 (UTC) Received: from [10.36.112.194] (ovpn-112-194.ams2.redhat.com [10.36.112.194]) by smtp.corp.redhat.com (Postfix) with ESMTP id D9B551F456; Fri, 5 Mar 2021 18:24:21 +0000 (UTC) Subject: Re: [PATCH V3 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory To: Catalin Marinas , Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Will Deacon , Ard Biesheuvel , Mark Rutland , James Morse , Robin Murphy , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Dan Williams , Mike Rapoport , Veronika Kabatova References: <1614921898-4099-1-git-send-email-anshuman.khandual@arm.com> <1614921898-4099-2-git-send-email-anshuman.khandual@arm.com> <20210305181322.GI23855@arm.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Fri, 5 Mar 2021 19:24:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210305181322.GI23855@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BA14740B8CEA X-Stat-Signature: xi437mpxq71ku8m3ujrd66534pw6cmk4 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614968677-514036 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 05.03.21 19:13, Catalin Marinas wrote: > On Fri, Mar 05, 2021 at 10:54:57AM +0530, Anshuman Khandual wrote: >> pfn_valid() validates a pfn but basically it checks for a valid struct page >> backing for that pfn. It should always return positive for memory ranges >> backed with struct page mapping. But currently pfn_valid() fails for all >> ZONE_DEVICE based memory types even though they have struct page mapping. >> >> pfn_valid() asserts that there is a memblock entry for a given pfn without >> MEMBLOCK_NOMAP flag being set. The problem with ZONE_DEVICE based memory is >> that they do not have memblock entries. Hence memblock_is_map_memory() will >> invariably fail via memblock_search() for a ZONE_DEVICE based address. This >> eventually fails pfn_valid() which is wrong. memblock_is_map_memory() needs >> to be skipped for such memory ranges. As ZONE_DEVICE memory gets hotplugged >> into the system via memremap_pages() called from a driver, their respective >> memory sections will not have SECTION_IS_EARLY set. >> >> Normal hotplug memory will never have MEMBLOCK_NOMAP set in their memblock >> regions. Because the flag MEMBLOCK_NOMAP was specifically designed and set >> for firmware reserved memory regions. memblock_is_map_memory() can just be >> skipped as its always going to be positive and that will be an optimization >> for the normal hotplug memory. Like ZONE_DEVICE based memory, all normal >> hotplugged memory too will not have SECTION_IS_EARLY set for their sections >> >> Skipping memblock_is_map_memory() for all non early memory sections would >> fix pfn_valid() problem for ZONE_DEVICE based memory and also improve its >> performance for normal hotplug memory as well. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Ard Biesheuvel >> Cc: Robin Murphy >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Acked-by: David Hildenbrand >> Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") >> Signed-off-by: Anshuman Khandual >> --- >> arch/arm64/mm/init.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >> index 0ace5e68efba..5920c527845a 100644 >> --- a/arch/arm64/mm/init.c >> +++ b/arch/arm64/mm/init.c >> @@ -230,6 +230,18 @@ int pfn_valid(unsigned long pfn) >> >> if (!valid_section(__pfn_to_section(pfn))) >> return 0; >> + >> + /* >> + * ZONE_DEVICE memory does not have the memblock entries. >> + * memblock_is_map_memory() check for ZONE_DEVICE based >> + * addresses will always fail. Even the normal hotplugged >> + * memory will never have MEMBLOCK_NOMAP flag set in their >> + * memblock entries. Skip memblock search for all non early >> + * memory sections covering all of hotplug memory including >> + * both normal and ZONE_DEVICE based. >> + */ >> + if (!early_section(__pfn_to_section(pfn))) >> + return pfn_section_valid(__pfn_to_section(pfn), pfn); > > Would something like this work instead: > > if (online_device_section(ms)) > return 1; > > to avoid the assumptions around early_section()? > Please keep online section logic out of pfn valid logic. Tow different things. (and rather not diverge too much from generic pfn_valid() - we want to achieve the opposite in the long term, merging both implementations) -- Thanks, David / dhildenb