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

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Message-ID: <20260120075507.GA2071@k08j02272.eu95sqa>
Date: Tue, 20 Jan 2026 15:55:07 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: Jürgen Groß <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org,
	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>, kvm@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH RESEND v2] x86/xen/pvh: Enable PAE mode for 32-bit guest
 only when CONFIG_X86_PAE is set

On Tue, Jan 20, 2026 at 08:48:43AM +0100, Jürgen Groß wrote:
> On 20.01.26 08:39, Hou Wenlong wrote:
> >+kvm, I'm not sure whether it is needed.
> 
> I have queued it in the Xen tree for the next merge window.
>
Thanks for the notification.
 
> 
> Juergen
> 
> >
> >On Sat, Jan 10, 2026 at 12:00:08PM +0800, Hou Wenlong wrote:
> >>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
> >>
> >>
> 

> pub  2048R/28BF132F 2014-06-02 Juergen Gross <jg@...pf.net>
> uid                            Juergen Gross <jgross@...e.com>
> uid                            Juergen Gross <jgross@...ell.com>
> uid                            Juergen Gross <jgross@...e.de>
> sub  2048R/16375B53 2014-06-02