linux-kernel - Re: [PATCH V5 1/3] riscv: mm: Prepare for reusing PTE RSW bit(9)

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Message-ID: <Z6rLlkphtv99+bH3@debug.ba.rivosinc.com>
Date: Mon, 10 Feb 2025 20:01:26 -0800
From: Deepak Gupta <debug@...osinc.com>
To: Chunyan Zhang <zhang.lyra@...il.com>
Cc: Björn Töpel <bjorn@...nel.org>,
	Chunyan Zhang <zhangchunyan@...as.ac.cn>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Alexandre Ghiti <alex@...ti.fr>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org
Subject: Re: [PATCH V5 1/3] riscv: mm: Prepare for reusing PTE RSW bit(9)

On Tue, Feb 11, 2025 at 09:20:22AM +0800, Chunyan Zhang wrote:
>On Thu, 30 Jan 2025 at 16:42, Björn Töpel <bjorn@...nel.org> wrote:
>>
>> Chunyan Zhang <zhangchunyan@...as.ac.cn> writes:
>>
>> > The PTE bit(9) on RISC-V is reserved for software, it is used by devmap
>> > now which has to be disabled if we want to use bit(9) for other features,
>> > since there's no more free PTE bit on RISC-V now.
>> >
>> > So to make ARCH_HAS_PTE_DEVMAP selectable, this patch uses it as
>> > the build condition of devmap definitions.
>>
>> Heads-up: It seems like Alistair's series [1] that removes the devmap
>> PTE bit will most likely land in 6.15.
>
>Yes, I've been keeping an eye on Alistair's series, intended to update
>this patchset after Alistair's patch that removes the devmap PTE bit
>got merged.

Please keep in mind that even after claiming back devmap PTE SW bit, a compile
time decision to select between uffd-wp and soft-dirty is not desirable.

>
>Thanks,
>Chunyan
>>
>>
>> Björn
>>
>> [1] https://lore.kernel.org/linux-mm/cover.11189864684e31260d1408779fac9db80122047b.1736488799.git-series.apopple@nvidia.com/
>