From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Lorenzo Stoakes <ljs@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>,
Linu Cherian <linu.cherian@arm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH V2 06/14] arm64/mm: Enable fixmap with 5 level page table
Date: Wed, 16 Sep 2026 16:30:05 +0200 [thread overview]
Message-ID: <be1c0a62-4589-4fe4-a500-d3fe16a6e610@kernel.org> (raw)
In-Reply-To: <20260907035030.2839978-7-anshuman.khandual@arm.com>
On 9/7/26 05:50, Anshuman Khandual wrote:
> FEAT_D128 halves PTRS_PER_PXX thus shrinking the VA range coverage
> for each page table level. Hence in order to preserve all existing
> VA range configurations, some geometry now need to become 5-level.
>
Hmm, wasn't this 5-levels before, but other code allocated+initialized the p4d
table for us?
I mean, I see how we are filling in another level, but I don't see how we would
reconfigure something to use 5 page table levels?
> Since fixmap is used to build and manipulate page tables early on
> during boot the mapping must also gain that additional level which
> was not required earlier.
I am no expert ... but I am confused :)
We do have a loop only in early_fixmap_init_pmd(). So we cannot possibly span
more than a single ... PTE table?
>
> Enable fixmap with 5 level page table when required. This creates table
> entries at the PGD level. Add a fallback stub for pgd_page_paddr() when
> (PGTBALE_LEVELS <= 4) which helps in intercepting any unintended usage.
Again, I am very confused. Is it really just "As the page table layout changes,
we might no longer have a p4d table pre-populated for the range our fixmap falls
into. So if there is no p4d table yet, populate a static one just like we do for
the other levels."
--
Cheers,
David
next prev parent reply other threads:[~2026-09-16 14:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-07 3:50 [PATCH V2 00/14] arm64/mm: Enable 128 bit page table entries Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 01/14] mm: Add read-write accessors for vm_page_prot Anshuman Khandual
2026-09-16 13:23 ` David Hildenbrand (Arm)
2026-09-16 13:41 ` Lorenzo Stoakes (ARM)
2026-09-07 3:50 ` [PATCH V2 02/14] arm64/mm: Route all pgtable reads via ptval_get() Anshuman Khandual
2026-09-16 13:35 ` David Hildenbrand (Arm)
2026-09-16 13:38 ` David Hildenbrand (Arm)
2026-09-07 3:50 ` [PATCH V2 03/14] arm64/mm: Route all pgtable writes via ptval_set() Anshuman Khandual
2026-09-16 13:36 ` David Hildenbrand (Arm)
2026-09-07 3:50 ` [PATCH V2 04/14] arm64/mm: Route all pgtable atomics to central helpers Anshuman Khandual
2026-09-16 13:39 ` David Hildenbrand (Arm)
2026-09-07 3:50 ` [PATCH V2 05/14] arm64/mm: Override read-write accessors for vm_page_prot Anshuman Khandual
2026-09-16 13:39 ` David Hildenbrand (Arm)
2026-09-07 3:50 ` [PATCH V2 06/14] arm64/mm: Enable fixmap with 5 level page table Anshuman Khandual
2026-09-16 14:30 ` David Hildenbrand (Arm) [this message]
2026-09-07 3:50 ` [PATCH V2 07/14] arm64/mm: Enable pgtable geometry for FEAT_D128 Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 08/14] arm64/mm: Enable pgtable descriptor " Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 09/14] arm64/mm: Enable 128 bit translation Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 10/14] arm64/mm: Add an abstraction level for tlbi_op Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 11/14] arm64/mm: Enable TLBIP instruction based TLB flush Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 12/14] arm64/mm: Relax KASAN shadow alignment for FEAT_D128 Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 13/14] arm64/mm: Make ARM64_D128 selectable Anshuman Khandual
2026-09-07 3:50 ` [PATCH V2 14/14] arm64/configs: Add d128.config Anshuman Khandual
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 \
--in-reply-to=be1c0a62-4589-4fe4-a500-d3fe16a6e610@kernel.org \
--to=david@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=catalin.marinas@arm.com \
--cc=linu.cherian@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ljs@kernel.org \
--cc=mark.rutland@arm.com \
--cc=rppt@kernel.org \
--cc=ryan.roberts@arm.com \
--cc=will@kernel.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®