From: Ryan Roberts <ryan.roberts@arm.com> To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Joey Gouly <joey.gouly@arm.com>, Ard Biesheuvel <ardb@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Anshuman Khandual <anshuman.khandual@arm.com>, David Hildenbrand <david@redhat.com>, Peter Xu <peterx@redhat.com>, Mike Rapoport <rppt@linux.ibm.com>, Shivansh Vij <shivanshvij@outlook.com> Cc: Ryan Roberts <ryan.roberts@arm.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v1 0/2] arm64/mm: Enable userfaultfd write-protect Date: Wed, 24 Apr 2024 12:10:15 +0100 [thread overview] Message-ID: <20240424111017.3160195-1-ryan.roberts@arm.com> (raw) Hi All, This series adds uffd write-protect support for arm64. The patches are extracted, without change, from a wider RFC I posted at [1]. Previous attempts to add uffd-wp (and soft-dirty) have failed because of a perceived lack of available PTE SW bits. However it actually turns out that there are 2 available but they are hidden. PTE_PROT_NONE was previously occupying a SW bit, but it only applies when PTE_VALID is clear, so this is moved to overlay PTE_UXN in patch 1, freeing up the SW bit. Bit 63 is marked as "IGNORED" in the Arm ARM, but it does not currently indicate "reserved for SW use" like it does for the other SW bits. I've confirmed with the spec owner that this is an oversight; the bit is intended to be reserved for SW use and the spec will clarify this in a future update. So now we have two spare bits; patch 2 enables uffd-wp on arm64, using the SW bit freed up by moving PTE_PROT_NONE. This leaves bit 63 spare for future use (e.g. soft-dirty - see RFC at [1] - or some other usage). This applies on top of v6.9-rc3. The all mm selftests involving uffd-wp now run and pass and no other selftest regressions are observed. [1] https://lore.kernel.org/all/20240419074344.2643212-1-ryan.roberts@arm.com/ Thanks, Ryan Ryan Roberts (2): arm64/mm: Move PTE_PROT_NONE and PMD_PRESENT_INVALID arm64/mm: Add uffd write-protect support arch/arm64/Kconfig | 1 + arch/arm64/include/asm/pgtable-prot.h | 12 ++++- arch/arm64/include/asm/pgtable.h | 71 ++++++++++++++++++++++++--- 3 files changed, 75 insertions(+), 9 deletions(-) -- 2.25.1
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From: Ryan Roberts <ryan.roberts@arm.com> To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Joey Gouly <joey.gouly@arm.com>, Ard Biesheuvel <ardb@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Anshuman Khandual <anshuman.khandual@arm.com>, David Hildenbrand <david@redhat.com>, Peter Xu <peterx@redhat.com>, Mike Rapoport <rppt@linux.ibm.com>, Shivansh Vij <shivanshvij@outlook.com> Cc: Ryan Roberts <ryan.roberts@arm.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v1 0/2] arm64/mm: Enable userfaultfd write-protect Date: Wed, 24 Apr 2024 12:10:15 +0100 [thread overview] Message-ID: <20240424111017.3160195-1-ryan.roberts@arm.com> (raw) Hi All, This series adds uffd write-protect support for arm64. The patches are extracted, without change, from a wider RFC I posted at [1]. Previous attempts to add uffd-wp (and soft-dirty) have failed because of a perceived lack of available PTE SW bits. However it actually turns out that there are 2 available but they are hidden. PTE_PROT_NONE was previously occupying a SW bit, but it only applies when PTE_VALID is clear, so this is moved to overlay PTE_UXN in patch 1, freeing up the SW bit. Bit 63 is marked as "IGNORED" in the Arm ARM, but it does not currently indicate "reserved for SW use" like it does for the other SW bits. I've confirmed with the spec owner that this is an oversight; the bit is intended to be reserved for SW use and the spec will clarify this in a future update. So now we have two spare bits; patch 2 enables uffd-wp on arm64, using the SW bit freed up by moving PTE_PROT_NONE. This leaves bit 63 spare for future use (e.g. soft-dirty - see RFC at [1] - or some other usage). This applies on top of v6.9-rc3. The all mm selftests involving uffd-wp now run and pass and no other selftest regressions are observed. [1] https://lore.kernel.org/all/20240419074344.2643212-1-ryan.roberts@arm.com/ Thanks, Ryan Ryan Roberts (2): arm64/mm: Move PTE_PROT_NONE and PMD_PRESENT_INVALID arm64/mm: Add uffd write-protect support arch/arm64/Kconfig | 1 + arch/arm64/include/asm/pgtable-prot.h | 12 ++++- arch/arm64/include/asm/pgtable.h | 71 ++++++++++++++++++++++++--- 3 files changed, 75 insertions(+), 9 deletions(-) -- 2.25.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2024-04-24 11:10 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-24 11:10 Ryan Roberts [this message] 2024-04-24 11:10 ` [PATCH v1 0/2] arm64/mm: Enable userfaultfd write-protect Ryan Roberts 2024-04-24 11:10 ` [PATCH v1 1/2] arm64/mm: Move PTE_PROT_NONE and PMD_PRESENT_INVALID Ryan Roberts 2024-04-24 11:10 ` Ryan Roberts 2024-04-24 16:43 ` Catalin Marinas 2024-04-24 16:43 ` Catalin Marinas 2024-04-25 8:40 ` Ryan Roberts 2024-04-25 8:40 ` Ryan Roberts 2024-04-25 9:16 ` David Hildenbrand 2024-04-25 9:16 ` David Hildenbrand 2024-04-25 10:29 ` Ryan Roberts 2024-04-25 10:29 ` Ryan Roberts 2024-04-25 10:37 ` Ryan Roberts 2024-04-25 10:37 ` Ryan Roberts 2024-04-26 14:48 ` Catalin Marinas 2024-04-26 14:48 ` Catalin Marinas 2024-04-29 10:04 ` Ryan Roberts 2024-04-29 10:04 ` Ryan Roberts 2024-04-29 12:38 ` Catalin Marinas 2024-04-29 12:38 ` Catalin Marinas 2024-04-29 13:01 ` Ryan Roberts 2024-04-29 13:01 ` Ryan Roberts 2024-04-29 13:23 ` Ryan Roberts 2024-04-29 13:23 ` Ryan Roberts 2024-04-29 14:18 ` Catalin Marinas 2024-04-29 14:18 ` Catalin Marinas 2024-04-29 15:04 ` Ryan Roberts 2024-04-29 15:04 ` Ryan Roberts 2024-04-24 11:10 ` [PATCH v1 2/2] arm64/mm: Add uffd write-protect support Ryan Roberts 2024-04-24 11:10 ` Ryan Roberts 2024-04-24 11:57 ` Peter Xu 2024-04-24 11:57 ` Peter Xu 2024-04-24 12:51 ` Ryan Roberts 2024-04-24 12:51 ` Ryan Roberts 2024-04-26 13:17 ` Ryan Roberts 2024-04-26 13:17 ` Ryan Roberts 2024-04-26 13:54 ` Peter Xu 2024-04-26 13:54 ` Peter Xu 2024-04-29 9:39 ` Ryan Roberts 2024-04-29 9:39 ` Ryan Roberts 2024-04-24 16:46 ` Catalin Marinas 2024-04-24 16:46 ` Catalin Marinas
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