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: <20260120073927.GA119722@k08j02272.eu95sqa>
Date: Tue, 20 Jan 2026 15:39:27 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: linux-kernel@...r.kernel.org
Cc: 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>, 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

+kvm, I'm not sure whether it is needed.

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
> 
>