From: David Hildenbrand <email@example.com> To: Ard Biesheuvel <firstname.lastname@example.org> Cc: Mike Rapoport <email@example.com>, Linux ARM <firstname.lastname@example.org>, Anshuman Khandual <email@example.com>, Catalin Marinas <firstname.lastname@example.org>, Marc Zyngier <email@example.com>, Mark Rutland <firstname.lastname@example.org>, Mike Rapoport <email@example.com>, Will Deacon <firstname.lastname@example.org>, kvmarm <email@example.com>, Linux Kernel Mailing List <firstname.lastname@example.org>, Linux Memory Management List <email@example.com> Subject: Re: [RFC/RFT PATCH 1/3] memblock: update initialization of reserved pages Date: Wed, 14 Apr 2021 17:52:57 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <CAMj1kXGw97epyP2HdHjA8Yp6+VF1j5xmd0AgVBBv3k+h_B610w@mail.gmail.com> On 14.04.21 17:27, Ard Biesheuvel wrote: > On Wed, 14 Apr 2021 at 17:14, David Hildenbrand <email@example.com> wrote: >> >> On 07.04.21 19:26, Mike Rapoport wrote: >>> From: Mike Rapoport <firstname.lastname@example.org> >>> >>> The struct pages representing a reserved memory region are initialized >>> using reserve_bootmem_range() function. This function is called for each >>> reserved region just before the memory is freed from memblock to the buddy >>> page allocator. >>> >>> The struct pages for MEMBLOCK_NOMAP regions are kept with the default >>> values set by the memory map initialization which makes it necessary to >>> have a special treatment for such pages in pfn_valid() and >>> pfn_valid_within(). >> >> I assume these pages are never given to the buddy, because we don't have >> a direct mapping. So to the kernel, it's essentially just like a memory >> hole with benefits. >> >> I can spot that we want to export such memory like any special memory >> thingy/hole in /proc/iomem -- "reserved", which makes sense. >> >> I would assume that MEMBLOCK_NOMAP is a special type of *reserved* >> memory. IOW, that for_each_reserved_mem_range() should already succeed >> on these as well -- we should mark anything that is MEMBLOCK_NOMAP >> implicitly as reserved. Or are there valid reasons not to do so? What >> can anyone do with that memory? >> >> I assume they are pretty much useless for the kernel, right? Like other >> reserved memory ranges. >> > > On ARM, we need to know whether any physical regions that do not > contain system memory contain something with device semantics or not. > One of the examples is ACPI tables: these are in reserved memory, and > so they are not covered by the linear region. However, when the ACPI > core ioremap()s an arbitrary memory region, we don't know whether it > is mapping a memory region or a device region unless we keep track of > this in some way. (Device mappings require device attributes, but > firmware tables require memory attributes, as they might be accessed > using misaligned reads) Using generically sounding NOMAP ("don't create direct mapping") to identify device regions feels like a hack. I know, it was introduced just for that purpose. Looking at memblock_mark_nomap(), we consider "device regions" 1) ACPI tables 2) VIDEO_TYPE_EFI memory 3) some device-tree regions in of/fdt.c IIUC, right now we end up creating a memmap for this NOMAP memory, but hide it away in pfn_valid(). This patch set at least fixes that. Assuming these pages are never mapped to user space via the struct page (which better be the case), we could further use a new pagetype to mark these pages in a special way, such that we can identify them directly via pfn_to_page(). Then, we could mostly avoid having to query memblock at runtime to figure out that this is special memory. This would obviously be an extension to this series. Just a thought. -- Thanks, David / dhildenb
next prev parent reply other threads:[~2021-04-14 15:54 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-07 17:26 [RFC/RFT PATCH 0/3] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport 2021-04-07 17:26 ` [RFC/RFT PATCH 1/3] memblock: update initialization of reserved pages Mike Rapoport 2021-04-08 5:16 ` Anshuman Khandual 2021-04-08 5:48 ` Mike Rapoport 2021-04-14 15:12 ` David Hildenbrand 2021-04-14 15:27 ` Ard Biesheuvel 2021-04-14 15:52 ` David Hildenbrand [this message] 2021-04-14 20:24 ` Mike Rapoport 2021-04-15 9:30 ` David Hildenbrand 2021-04-16 11:44 ` Mike Rapoport 2021-04-16 11:54 ` David Hildenbrand 2021-04-14 20:11 ` Mike Rapoport 2021-04-14 20:06 ` Mike Rapoport 2021-04-07 17:26 ` [RFC/RFT PATCH 2/3] arm64: decouple check whether pfn is normal memory from pfn_valid() Mike Rapoport 2021-04-08 5:14 ` Anshuman Khandual 2021-04-08 6:00 ` Mike Rapoport 2021-04-14 15:58 ` David Hildenbrand 2021-04-14 20:29 ` Mike Rapoport 2021-04-15 9:31 ` David Hildenbrand 2021-04-16 11:40 ` Mike Rapoport 2021-04-07 17:26 ` [RFC/RFT PATCH 3/3] arm64: drop pfn_valid_within() and simplify pfn_valid() Mike Rapoport 2021-04-08 5:12 ` Anshuman Khandual 2021-04-08 6:17 ` Mike Rapoport 2021-04-08 5:19 ` [RFC/RFT PATCH 0/3] " Anshuman Khandual 2021-04-08 6:27 ` Mike Rapoport
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [RFC/RFT PATCH 1/3] memblock: update initialization of reserved pages' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).