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Date: Sun, 4 Oct 2026 22:47:39 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Lance Yang <lance.yang@linux.dev>
Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
 tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
 hpa@zytor.com, riel@surriel.com, linux-kernel@vger.kernel.org,
 qi.zheng@linux.dev, nadav.amit@gmail.com, thomas.lendacky@amd.com,
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 Manali.Shukla@amd.com, mingo@kernel.org, stable@vger.kernel.org,
 toshi.kani@hpe.com, david@kernel.org, mikhail.v.gavrilov@gmail.com,
 pfalcato@suse.de
Subject: Re: [PATCH 1/1] x86/mm: fix incomplete page-table invalidation with
 TCE
Message-Id: <20261004224739.e1049f07332d388169f7ef08@linux-foundation.org>
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On Mon,  5 Oct 2026 13:23:02 +0800 Lance Yang <lance.yang@linux.dev> wrote:

> pud_free_pmd_page() uses a single-address invalidation to flush the
> paging-structure caches before freeing the page tables. With AMD TCE
> enabled, this only invalidates upper-level entries associated with the
> target address. Cached PMD entries for other addresses in the PUD range can
> still reference the PTE pages being freed.
> 
> The AMD manual quoted in the commit enabling TCE says these instructions
> remove
> 
>   "only those upper-level entries that lead to the target PTE in the page
>   table hierarchy, leaving unrelated upper-level entries intact."
> 
> Even with all PTEs cleared, speculative page walks can cache present PMD
> entries after the earlier TLB purge.
> 
> Use a full TLB flush before freeing the page tables on CPUs with TCE. Keep
> the single-address invalidation otherwise.
> 
> Fixes: 440a65b7d25f ("x86/mm: Enable AMD translation cache extensions")
> Cc: stable@vger.kernel.org

Sorry, but my usual complaint applies.

Check the first 32 lines of
Documentation/process/stable-kernel-rules.rst.  They're very simple,

I'm sure x86 people can immediately grasp the importance of this
change, but nobody else can.  This includes -stable maintainers as well
as a large number of other downstream users of our work who are
wondering "why should I apply this to my kernel".  Let's tell them!


iow, and not for the first time: when fixing a bug please fully
describe the userspace-visible runtime effects of that bug.

Thanks.