linux-kernel - [PATCH RESEND v2] x86/xen/pvh: Enable PAE mode for 32-bit guest only when CONFIG_X86

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Message-Id: <d09ce9a134eb9cbc16928a5b316969f8ba606b81.1768017442.git.houwenlong.hwl@antgroup.com>
Date: Sat, 10 Jan 2026 12:00:08 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: linux-kernel@...r.kernel.org
Cc: Hou Wenlong <houwenlong.hwl@...group.com>,
	Juergen Gross <jgross@...e.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	xen-devel@...ts.xenproject.org
Subject: [PATCH RESEND v2] x86/xen/pvh: Enable PAE mode for 32-bit guest only when CONFIG_X86_PAE is set

The PVH entry is available for 32-bit KVM guests, and 32-bit KVM guests
do not depend on CONFIG_X86_PAE. However, mk_early_pgtbl_32() builds
different pagetables depending on whether CONFIG_X86_PAE is set.
Therefore, enabling PAE mode for 32-bit KVM guests without
CONFIG_X86_PAE being set would result in a boot failure during CR3
loading.

Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Reviewed-by: Juergen Gross <jgross@...e.com>
---
I resend this because I encountered the 32-bit KVM guest PVH booting failure again. I
hope this can be fixed.
original v2:
https://lore.kernel.org/all/0469c27833be58aa66471920aa77922489d86c63.1713873613.git.houwenlong.hwl@antgroup.com
---
 arch/x86/platform/pvh/head.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index 344030c1a81d..53ee2d53fcf8 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -91,10 +91,12 @@ SYM_CODE_START(pvh_start_xen)
 
 	leal rva(early_stack_end)(%ebp), %esp
 
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
 	/* Enable PAE mode. */
 	mov %cr4, %eax
 	orl $X86_CR4_PAE, %eax
 	mov %eax, %cr4
+#endif
 
 #ifdef CONFIG_X86_64
 	/* Enable Long mode. */

base-commit: b7dccac786071bba98b0d834c517fd44a22c50f9
prerequisite-patch-id: 590fa7e96c6bb8e0b9d15017cfa5ce1eb314957a
-- 
2.31.1