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From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org
Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Dave P Martin <Dave.Martin@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v6 07/26] mm: Preserve the PG_arch_* flags in __split_huge_page_tail()
Date: Mon, 6 Jul 2020 16:16:13 +0200	[thread overview]
Message-ID: <16aeea8c-b5c4-0d19-2fde-f95ef8dfddc6@redhat.com> (raw)
In-Reply-To: <20200703153718.16973-8-catalin.marinas@arm.com>

On 03.07.20 17:36, Catalin Marinas wrote:
> When a huge page is split into normal pages, part of the head page flags
> are transferred to the tail pages. However, the PG_arch_* flags are not
> part of the preserved set.
> 
> PG_arch_1 is currently used by the arch code to handle cache maintenance
> for user space (either for I-D cache coherency or for D-cache aliases
> consistent with the kernel mapping). Since splitting a huge page does
> not change the physical or virtual address of a mapping, additional
> cache maintenance for the tail pages is unnecessary. Preserving the
> PG_arch_1 flag from the head page in the tail pages would not break the
> current use-cases.

^ is fairly arm64 specific, no? (I remember that the semantics are
different e.g., on s390x).

Did you check if this is actually safe to do on other architectures?
Maybe rephrase the description to make this clearer.

> 
> PG_arch_2 is currently used for arm64 MTE support to mark pages that
> have valid tags. The absence of such flag causes the arm64 set_pte_at()
> to clear the tags in order to avoid stale tags exposed to user or the
> swapping out hooks to ignore the tags. Not preserving PG_arch_2 on huge
> page splitting leads to tag corruption in the tail pages.

"currently"? I don't think so - isn't it follow-up patches in this series?

> 
> To avoid the above and for consistency between the two PG_arch_* flags,
> preserve both PG_arch_1 and PG_arch_2 in __split_huge_page_tail().
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
> Notes:
>     New in v6.
> 
>  mm/huge_memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 78c84bee7e29..22b3236a6dd8 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2364,6 +2364,10 @@ static void __split_huge_page_tail(struct page *head, int tail,
>  			 (1L << PG_workingset) |
>  			 (1L << PG_locked) |
>  			 (1L << PG_unevictable) |
> +			 (1L << PG_arch_1) |
> +#ifdef CONFIG_64BIT
> +			 (1L << PG_arch_2) |
> +#endif
>  			 (1L << PG_dirty)));
>  
>  	/* ->mapping in first tail page is compound_mapcount */
> 


-- 
Thanks,

David / dhildenb

  reply	other threads:[~2020-07-06 14:16 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-03 15:36 [PATCH v6 00/26] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-07-03 15:36 ` Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 01/26] arm64: mte: system register definitions Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 02/26] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-07-13 10:08   ` Steven Price
2020-07-13 17:45     ` Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 03/26] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 04/26] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 05/26] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 06/26] mm: Add PG_arch_2 page flag Catalin Marinas
2020-07-06  8:24   ` David Hildenbrand
2020-07-06  8:24     ` David Hildenbrand
2020-07-06 11:21     ` Catalin Marinas
2020-07-06 12:42       ` David Hildenbrand
2020-07-06 12:42         ` David Hildenbrand
2020-07-03 15:36 ` [PATCH v6 07/26] mm: Preserve the PG_arch_* flags in __split_huge_page_tail() Catalin Marinas
2020-07-06 14:16   ` David Hildenbrand [this message]
2020-07-06 14:16     ` David Hildenbrand
2020-07-06 16:30     ` Catalin Marinas
2020-07-06 17:56       ` David Hildenbrand
2020-07-08 12:17         ` Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 08/26] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 09/26] arm64: mte: Tags-aware copy_{user_,}highpage() implementations Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 10/26] arm64: Avoid unnecessary clear_user_page() indirection Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 11/26] arm64: mte: Tags-aware aware memcmp_pages() implementation Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 12/26] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 13/26] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 14/26] mm: Introduce arch_validate_flags() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 15/26] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 16/26] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 17/26] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 18/26] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 19/26] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 20/26] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-07-09 14:41   ` Luis Machado
2020-07-03 15:37 ` [PATCH v6 21/26] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 22/26] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 23/26] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 24/26] arm64: mte: Save tags when hibernating Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 25/26] arm64: mte: Kconfig entry Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 26/26] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-07-09  9:32   ` Szabolcs Nagy
2020-07-09 14:43     ` Catalin Marinas

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