linux-kernel - Re: [PATCH v2 2/5] KVM: arm64: Support set the DBM attr during memory abort

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Message-ID: <9fab5f94-33f2-419b-b0fb-200c7dbc8912@huawei.com>
Date: Thu, 27 Nov 2025 20:19:30 +0800
From: Tian Zheng <zhengtian10@...wei.com>
To: Marc Zyngier <maz@...nel.org>, Tian Zheng <zhengtian10@...wei.com>
CC: <oliver.upton@...ux.dev>, <catalin.marinas@....com>, <corbet@....net>,
	<pbonzini@...hat.com>, <will@...nel.org>, <linux-kernel@...r.kernel.org>,
	<yuzenghui@...wei.com>, <wangzhou1@...ilicon.com>, <yezhenyu2@...wei.com>,
	<xiexiangyou@...wei.com>, <zhengchuan@...wei.com>, <joey.gouly@....com>,
	<kvmarm@...ts.linux.dev>, <kvm@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
	<suzuki.poulose@....com>
Subject: Re: [PATCH v2 2/5] KVM: arm64: Support set the DBM attr during memory
 abort



On 2025/11/22 20:54, Marc Zyngier wrote:
> On Fri, 21 Nov 2025 09:23:39 +0000,
> Tian Zheng <zhengtian10@...wei.com> wrote:
>>
>> From: eillon <yezhenyu2@...wei.com>
>>
>> Add DBM support to automatically promote write-clean pages to
>> write-dirty, preventing users from being trapped in EL2 due to
>> missing write permissions.
>>
>> Since the DBM attribute was introduced in ARMv8.1 and remains
>> optional in later architecture revisions, including ARMv9.5.
> 
> What is the relevance of this statement?
> 
I will remove this statement in v3.
>>
>> Support set the DBM attr during user_mem_abort().
> 
> I don't think this commit message accurately describes what the code
> does. This merely adds support to the page table code to set the DBM
> bit in the S2 PTE, and nothing else.
> 
Yes, this patch only adds support to set the DBM attr in the S2 PTE
during user_mem_abort(), and does not implement automatic promote
write-clean pages to write-dirty.

I will reward commit message of this patch like:

This patch adds support to set the DBM attr in S2 PTE during
user_mem_abort(). As long as add the DBM bit, it enable hardware
automatically promote write-clean pages to write-dirty, preventing
users from being trapped in EL2 due to missing write permissions.

> 	M.
>