From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Will Deacon" <will@kernel.org>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"James Morse" <james.morse@arm.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Mike Rapoport" <rppt@linux.ibm.com>,
"Veronika Kabatova" <vkabatov@redhat.com>
Subject: Re: [PATCH V3 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory
Date: Fri, 5 Mar 2021 19:24:21 +0100 [thread overview]
Message-ID: <e446810c-2020-9f21-79ba-6ede473447da@redhat.com> (raw)
In-Reply-To: <20210305181322.GI23855@arm.com>
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 <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Ard Biesheuvel <ardb@kernel.org>
>> Cc: Robin Murphy <robin.murphy@arm.com>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support")
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>> 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
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next prev parent reply other threads:[~2021-03-05 18:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-05 5:24 [PATCH V3 0/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Anshuman Khandual
2021-03-05 5:24 ` [PATCH V3 1/2] " Anshuman Khandual
2021-03-05 18:13 ` Catalin Marinas
2021-03-05 18:24 ` David Hildenbrand [this message]
2021-03-08 11:29 ` Catalin Marinas
2021-03-08 17:59 ` Catalin Marinas
2021-03-05 5:24 ` [PATCH V3 2/2] arm64/mm: Reorganize pfn_valid() Anshuman Khandual
2021-03-08 18:00 ` Catalin Marinas
2021-03-05 5:38 ` [PATCH V3 0/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Anshuman Khandual
2021-03-05 12:28 ` Veronika Kabatova
2021-03-05 18:16 ` Veronika Kabatova
2021-03-05 18:22 ` Catalin Marinas
2021-03-08 19:16 ` Will Deacon
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