From: Dave Hansen <dave.hansen@intel.com>
To: Phineas Su <pohaosu@google.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
x86@kernel.org
Cc: "H . Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/mm: Clear PUD entry before populating PMD table when splitting 1GB page in phys_pud_init
Date: Mon, 20 Jul 2026 06:08:06 -0700 [thread overview]
Message-ID: <46b7a4b9-c185-4ddc-818e-9581fefb8f6e@intel.com> (raw)
In-Reply-To: <20260719182633.2196873-1-pohaosu@google.com>
On 7/19/26 11:26, Phineas Su wrote:
> When phys_pud_init() splits an existing 1 GB huge page (pud_leaf(*pud))
> into PMD table entries, it extracts the page protection attributes but
> does not clear the existing PUD entry (*pud).
>
> Subsequently, pud_populate_init() -> set_pud_safe() is invoked to link
> the new PMD table. Because *pud is still populated with the 1 GB huge
> page entry, set_pud_safe() detects a present entry that differs from the
> new PMD table pointer, triggering a WARN_ON_ONCE call trace in dmesg:
>
> WARNING: CPU: 0 PID: 0 at arch/x86/mm/init_64.c:89 phys_pud_init+0x2d6/0x390
>
> Call pud_clear(pud) right after extracting protection attributes when
> splitting the 1 GB page so that set_pud_safe() can populate the PMD
> table cleanly without issuing a warning.
Why aren't we running in to this left and right? I wouldn't think
splitting a PUD would be _that_ rare.
next prev parent reply other threads:[~2026-07-20 13:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-19 18:26 Phineas Su
2026-07-20 13:08 ` Dave Hansen [this message]
2026-07-21 17:42 ` Phineas Su
2026-07-21 18:02 ` [PATCH v2] x86/mm: Clear PUD/PMD entries when splitting huge pages Phineas Su
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