From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Ryan Roberts <ryan.roberts@arm.com>
Cc: 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>,
Peter Xu <peterx@redhat.com>, Mike Rapoport <rppt@linux.ibm.com>,
Shivansh Vij <shivanshvij@outlook.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and PTE_PROT_NONE bits
Date: Tue, 30 Apr 2024 13:37:53 +0200 [thread overview]
Message-ID: <29fd6909-73d2-4b7e-99ef-0101cde1ba8a@redhat.com> (raw)
In-Reply-To: <ZjDR0EIjLr9F2dWn@arm.com>
On 30.04.24 13:11, Catalin Marinas wrote:
> On Mon, Apr 29, 2024 at 06:15:45PM +0100, Ryan Roberts wrote:
>> On 29/04/2024 17:20, Catalin Marinas wrote:
>>> On Mon, Apr 29, 2024 at 03:02:05PM +0100, Ryan Roberts wrote:
>>>> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
>>>> index dd9ee67d1d87..de62e6881154 100644
>>>> --- a/arch/arm64/include/asm/pgtable-prot.h
>>>> +++ b/arch/arm64/include/asm/pgtable-prot.h
>>>> @@ -18,14 +18,7 @@
>>>> #define PTE_DIRTY (_AT(pteval_t, 1) << 55)
>>>> #define PTE_SPECIAL (_AT(pteval_t, 1) << 56)
>>>> #define PTE_DEVMAP (_AT(pteval_t, 1) << 57)
>>>> -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
>>>> -
>>>> -/*
>>>> - * This bit indicates that the entry is present i.e. pmd_page()
>>>> - * still points to a valid huge page in memory even if the pmd
>>>> - * has been invalidated.
>>>> - */
>>>> -#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */
>>>> +#define PTE_INVALID (_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */
>>>
>>> Nitpick - I prefer the PTE_PRESENT_INVALID name as it makes it clearer
>>> it's a present pte. We already have PTE_VALID, calling it PTE_INVALID
>>> looks like a negation only.
>>
>> Meh, for me the pte can only be valid or invalid if it is present. So it's
>> implicit. And if you have PTE_PRESENT_INVALID you should also have
>> PTE_PRESENT_VALID.
>>
>> We also have pte_mkinvalid(), which is core-mm-defined. In your scheme, surely
>> it should be pte_mkpresent_invalid()?
>>
>> But you're the boss, I'll change this to PTE_PRESENT_INVALID. :-(
>
> TBH, I don't have a strong opinion but best to avoid the bikeshedding.
> I'll leave the decision to you ;). It would match the pmd_mkinvalid()
> core code. But if you drop 'present' make sure you add a comment above
> that it's meant for present ptes.
FWIW, I was confused by
present = valid | invalid
Something like
present = present_valid | present_invalid
would be more obvious at least to me ;)
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2024-04-30 11:37 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-29 14:02 [PATCH v2 0/3] arm64/mm: Enable userfaultfd write-protect Ryan Roberts
2024-04-29 14:02 ` [PATCH v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and PTE_PROT_NONE bits Ryan Roberts
2024-04-29 16:12 ` David Hildenbrand
2024-04-29 16:20 ` Catalin Marinas
2024-04-29 17:15 ` Ryan Roberts
2024-04-30 11:11 ` Catalin Marinas
2024-04-30 11:35 ` Ryan Roberts
2024-04-30 13:28 ` Catalin Marinas
2024-04-30 13:34 ` Ryan Roberts
2024-04-30 11:37 ` David Hildenbrand [this message]
2024-04-30 12:53 ` Ryan Roberts
2024-04-30 12:58 ` David Hildenbrand
2024-04-30 13:30 ` Will Deacon
2024-04-30 14:02 ` Ryan Roberts
2024-04-30 15:04 ` Will Deacon
2024-04-30 15:39 ` Ryan Roberts
2024-04-29 14:02 ` [PATCH v2 2/3] arm64/mm: Move PTE_INVALID to overlay PTE_NS Ryan Roberts
2024-04-29 16:34 ` Catalin Marinas
2024-04-29 14:02 ` [PATCH v2 3/3] arm64/mm: Add uffd write-protect support Ryan Roberts
2024-04-29 16:08 ` David Hildenbrand
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