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: <409f5119-7dc1-4f45-a099-281db82254f3@suse.com>
Date: Tue, 20 Jan 2026 08:48:43 +0100
From: Jürgen Groß <jgross@...e.com>
To: Hou Wenlong <houwenlong.hwl@...group.com>, linux-kernel@...r.kernel.org
Cc: 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 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.


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
>>
>>


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