Messages in this thread Patch in this message | | | Subject | Re: [RFC 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory | From | David Hildenbrand <> | Date | Tue, 22 Dec 2020 10:11:40 +0100 |
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On 22.12.20 08:12, 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_DEVIE based memory, all hotplugged > normal 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 75addb36354a..ee23bda00c28 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -225,6 +225,18 @@ 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_DEVIE based. > + */ > + if (!early_section(__pfn_to_section(pfn))) > + return 1;
Actually, I think we want to check for partial present sections.
Maybe we can rather switch to generic pfn_valid() and tweak it to something like
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index fb3bf696c05e..7b1fcce5bd5a 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1382,9 +1382,13 @@ static inline int pfn_valid(unsigned long pfn) return 0; /* * Traditionally early sections always returned pfn_valid() for - * the entire section-sized span. + * the entire section-sized span. Some archs might have holes in + * early sections, so double check with memblock if configured. */ - return early_section(ms) || pfn_section_valid(ms, pfn); + if (early_section(ms)) + return IS_ENABLED(CONFIG_EARLY_SECTION_MEMMAP_HOLES) ? + memblock_is_map_memory(pfn << PAGE_SHIFT) : 1; + return pfn_section_valid(ms, pfn); } #endif
Which users are remaining that require us to add/remove memblocks when hot(un)plugging memory
$ git grep KEEP_MEM | grep memory_hotplug mm/memory_hotplug.c: if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) mm/memory_hotplug.c: if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) mm/memory_hotplug.c: if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
I think one user we would have to handle is arch/arm64/mm/mmap.c:valid_phys_addr_range(). AFAIS, powerpc at least does not rely on memblock_is_map_memory.
-- Thanks,
David / dhildenb
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