From: "David Hildenbrand (Arm)" <david@kernel.org>
To: James Houghton <jthoughton@google.com>,
Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Muchun Song <muchun.song@linux.dev>,
Oscar Salvador <osalvador@suse.de>
Cc: Nikos Nikoleris <nikos.nikoleris@arm.com>,
Linu Cherian <linu.cherian@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Nanyong Sun <sunnanyong@huawei.com>, Yu Zhao <yuzhao@google.com>,
Frank van der Linden <fvdl@google.com>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org
Subject: Re: [PATCH 00/18] Another attempt at HVO support on arm64
Date: Thu, 9 Jul 2026 11:58:03 +0200 [thread overview]
Message-ID: <42a5cd12-9569-4719-bd6e-95dc0100c065@kernel.org> (raw)
In-Reply-To: <20260708031129.3503195-1-jthoughton@google.com>
> -- The AF trick --
>
> The trick is that translations with the AF unset cannot be cached in the
> TLB (see Rule R_DWZCQ in the Arm ARM), so they can be atomically updated
> without needing a full break-before-make sequence.
>
> So the PTE update sequence becomes:
> 1. Atomically clear the AF on the existing PTE.
> 2. Invalidate the TLB.
> 3. cmpxchg the AF=0 PTE with the new PTE. If this fails, goto 1.
>
> If there is a CPU on the system that does not support hardware access
> flag updates, clearing the AF is problematic, as those CPUs might fault
> on the vmemmap usage. Therefore, HVO compatbility checks all CPUs for HW
> AF updates.
Pretty nice trick, I hope this will fly :)
--
Cheers,
David
next prev parent reply other threads:[~2026-07-09 9:58 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-08 3:11 [PATCH 00/18] Another attempt at HVO support on arm64 James Houghton
2026-07-08 3:11 ` [PATCH 01/18] hugetlb_vmemmap: Always flush TLB if needed upon PTE remapping James Houghton
2026-07-08 3:11 ` [PATCH 02/18] hugetlb_vmemmap: Move vmemmap_get_tail up James Houghton
2026-07-08 3:11 ` [PATCH 03/18] hugetlb_vmemmap: Leave pages partially HVOed upon restore failure James Houghton
2026-07-08 3:11 ` [PATCH 04/18] hugetlb_vmemmap: Use try_update_vmemmap_pte to update in-use PTEs James Houghton
2026-07-08 3:11 ` [PATCH 05/18] hugetlb_vmemmap: Allow architectures not to allow HVO at runtime James Houghton
2026-07-08 3:11 ` [PATCH 06/18] arm64: Rename cpu_has_hw_af to system_has_hw_af James Houghton
2026-07-08 3:11 ` [PATCH 07/18] arm64: Add system_supports_hvo James Houghton
2026-07-08 3:11 ` [PATCH 08/18] arm64: Implement try_update_vmemmap_pte using the AF trick James Houghton
2026-07-08 3:11 ` [PATCH 09/18] arm64: Prevent HVO if the HVO system feature is not enabled James Houghton
2026-07-08 3:11 ` [PATCH 10/18] arm64: Support hugetlb vmemmap optimization James Houghton
2026-07-08 3:11 ` [PATCH 11/18] hugetlb_vmemmap: Use try_populate_vmemmap_pmd for replacing in-use PMDs James Houghton
2026-07-08 3:11 ` [PATCH 12/18] arm64: Implement try_populate_vmemmap_pmd using AF trick James Houghton
2026-07-08 3:11 ` [PATCH 13/18] arm64: Drop BBML2_NOABORT requirement for HVO James Houghton
2026-07-08 3:11 ` [PATCH 14/18] hugetlb_vmemmap: Rename mm/hugetlb_vmemmap.h to mm/hugetlb_vmemmap_internal.h James Houghton
2026-07-08 3:11 ` [PATCH 15/18] hugetlb_vmemmap: Add a way to permanently disable HVO when needed James Houghton
2026-07-08 3:11 ` [PATCH 16/18] arm64: Allow "optional" CPU features to be required sometimes James Houghton
2026-07-08 3:11 ` [PATCH 17/18] arm64: Permit onlining of HVO-incompatible late CPUs if HVO is not in use James Houghton
2026-07-08 3:11 ` [PATCH 18/18] arm64: Remove user-selectable HVO Kconfig James Houghton
2026-07-08 8:40 ` [PATCH 00/18] Another attempt at HVO support on arm64 Muchun Song
2026-07-08 16:49 ` James Houghton
2026-07-09 9:54 ` Muchun Song
2026-07-09 19:04 ` James Houghton
2026-07-10 3:40 ` Muchun Song
2026-07-09 9:58 ` David Hildenbrand (Arm) [this message]
2026-07-10 4:58 ` Muchun Song
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