From: Will Deacon <will@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Catalin Marinas" <catalin.marinas@arm.com>,
"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>,
"David Hildenbrand" <david@redhat.com>,
"Mike Rapoport" <rppt@linux.ibm.com>
Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory
Date: Tue, 2 Feb 2021 12:35:24 +0000 [thread overview]
Message-ID: <20210202123524.GB16868@willie-the-truck> (raw)
In-Reply-To: <20210202123215.GA16868@willie-the-truck>
On Tue, Feb 02, 2021 at 12:32:15PM +0000, Will Deacon wrote:
> On Tue, Feb 02, 2021 at 09:41:53AM +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.
>
> Hmm. Although I follow your logic, this does seem to rely on an awful lot of
> assumptions to continue to hold true as the kernel evolves. In particular,
> how do we ensure that early sections are always fully backed with
Sorry, typo here: ^^^ should be *non-early* sections.
Will
next prev parent reply other threads:[~2021-02-02 12:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-02 4:11 [PATCH V2 0/2] " Anshuman Khandual
2021-02-02 4:11 ` [PATCH V2 1/2] " Anshuman Khandual
2021-02-02 12:32 ` Will Deacon
2021-02-02 12:35 ` Will Deacon [this message]
2021-02-02 12:39 ` David Hildenbrand
2021-02-02 12:51 ` Will Deacon
2021-02-02 12:56 ` David Hildenbrand
2021-02-03 3:50 ` Anshuman Khandual
2021-02-05 18:55 ` Will Deacon
2021-02-11 11:53 ` Will Deacon
2021-02-11 12:10 ` Anshuman Khandual
2021-02-11 12:21 ` Will Deacon
2021-02-11 12:35 ` David Hildenbrand
2021-03-03 19:04 ` Catalin Marinas
2021-03-03 19:24 ` David Hildenbrand
2021-03-03 21:24 ` Will Deacon
2021-03-04 3:31 ` Anshuman Khandual
2021-03-04 8:12 ` David Hildenbrand
2021-03-04 9:36 ` Will Deacon
2021-03-05 4:22 ` Anshuman Khandual
2021-02-02 4:11 ` [PATCH V2 2/2] arm64/mm: Reorganize pfn_valid() Anshuman Khandual
2021-02-02 8:26 ` David Hildenbrand
2021-02-05 18:52 ` [PATCH V2 0/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Will Deacon
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