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From: David Hildenbrand <david@redhat.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"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>
Subject: Re: [PATCH 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory
Date: Fri, 29 Jan 2021 10:58:59 +0100	[thread overview]
Message-ID: <31a1d742-843f-1837-8569-92b897190a81@redhat.com> (raw)
In-Reply-To: <1611905986-20155-2-git-send-email-anshuman.khandual@arm.com>

On 29.01.21 08:39, 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
> 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 709d98fea90c..1141075e4d53 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);
>   #endif
>   	return memblock_is_map_memory(addr);
>   }
> 

LGTM

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb



  reply	other threads:[~2021-01-29  9:59 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-29  7:39 [PATCH 0/2] " Anshuman Khandual
2021-01-29  7:39 ` [PATCH 1/2] " Anshuman Khandual
2021-01-29  9:58   ` David Hildenbrand [this message]
2021-01-29  7:39 ` [PATCH 2/2] arm64/mm: Reorganize pfn_valid() Anshuman Khandual
2021-01-29 10:07   ` David Hildenbrand
2021-02-01  3:47     ` Anshuman Khandual

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