linux-kernel - [PATCH 1/5] x86/mm/pat: don't collapse pages without PSE set

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Message-ID: <20250603111446.2609381-2-rppt@kernel.org>
Date: Tue,  3 Jun 2025 14:14:41 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jürgen Groß <jgross@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Xin Li <xin@...or.com>,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	x86@...nel.org
Subject: [PATCH 1/5] x86/mm/pat: don't collapse pages without PSE set

From: Juergen Gross <jgross@...e.com>

Collapsing pages to a leaf PMD or PUD should be done only if
X86_FEATURE_PSE is available, which is not the case when running e.g.
as a Xen PV guest.

Cc: stable@...r.kernel.org
Fixes: 41d88484c71c ("x86/mm/pat: restore large ROX pages after fragmentation")
Signed-off-by: Juergen Gross <jgross@...e.com>
Link: https://lore.kernel.org/r/20250528123557.12847-3-jgross@suse.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 arch/x86/mm/pat/set_memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index def3d9284254..9292f835cf5a 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1257,6 +1257,9 @@ static int collapse_pmd_page(pmd_t *pmd, unsigned long addr,
 	pgprot_t pgprot;
 	int i = 0;
 
+	if (!cpu_feature_enabled(X86_FEATURE_PSE))
+		return 0;
+
 	addr &= PMD_MASK;
 	pte = pte_offset_kernel(pmd, addr);
 	first = *pte;
-- 
2.47.2