From: Dave Hansen <dave.hansen@intel.com>
To: Kiryl Shutsemau <kas@kernel.org>,
Vernon Yang <vernon2gm@gmail.com>,
rick.p.edgecombe@intel.com
Cc: tglx@kernel.org, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, akpm@linux-foundation.org,
david@kernel.org, hpa@zytor.com, rmclure@linux.ibm.com,
andrew+kernel@donnellan.id.au, pasha.tatashin@soleen.com,
tj@kernel.org, rppt@kernel.org, yu-cheng.yu@intel.com,
orsonpeters@gmail.com, linux-kernel@vger.kernel.org,
x86@kernel.org, linux-mm@kvack.org,
Vernon Yang <yanglincheng@kylinos.cn>,
stable@vger.kernel.org
Subject: Re: [PATCH] x86/mm: Fix pmd_modify() dropping the dirty bit
Date: Thu, 3 Sep 2026 07:18:54 -0700 [thread overview]
Message-ID: <314f11c1-ce5e-4b36-b296-0ab742550851@intel.com> (raw)
In-Reply-To: <aplfcTfjeQUgnrvH@thinkstation>
On 9/3/26 04:54, Kiryl Shutsemau wrote:
>> Closes: https://lore.kernel.org/r/CAJxLxMUGu1-L+O_nAONOwOXnS=cNbNApCWqdthRjd76LThtSPg@mail.gmail.com/
>> Fixes: bb3aadf7d446 ("x86/mm: Start actually marking _PAGE_SAVED_DIRTY")
> Hm. I don't understand why would this commit explicitly exclude
> _PAGE_DIRTY from the mask:
>
> - val &= _HPAGE_CHG_MASK;
> + val &= (_HPAGE_CHG_MASK & ~_PAGE_DIRTY);
>
> Rick, could you comment? It doesn't look like a typo.
My guess is that it's some remnant from an earlier version of the patch.
The asymmetry with pte_modify() vs. pmd_modify() just can't be explained
any other way. It _might_ have been some attempt to say, "Hey
_PAGE_DIRTY is now a part of the pgprot_t since it's part of the
'permissions' of a shadow stack PTE" that got abandoned.
But I don't see anything wrong with the fix at all.
It does give me pause that this has been losing user data for so long,
but it must just be a weird combination of features that few folks use
together (huge pages + MADV_FREE).
next prev parent reply other threads:[~2026-09-03 14:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-03 3:16 [PATCH] x86/mm: Fix pmd_modify() dropping the dirty bit Vernon Yang
2026-09-03 4:10 ` Andrew Morton
2026-09-03 5:24 ` Vernon Yang
2026-09-03 7:34 ` Orson Peters
2026-09-03 15:40 ` Dave Hansen
2026-09-03 11:54 ` Kiryl Shutsemau
2026-09-03 14:18 ` Dave Hansen [this message]
2026-09-03 17:21 ` Andrew Morton
2026-09-03 17:58 ` Edgecombe, Rick P
2026-09-03 18:01 ` Dave Hansen
2026-09-03 18:33 ` Edgecombe, Rick P
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