linux-kernel - Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less confusion

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Date: Mon, 3 Jun 2024 17:24:00 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nikolay Borisov <nik.borisov@...e.com>
Cc: 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,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish"
 <ashish.kalra@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>, Ard Biesheuvel <ardb@...nel.org>,
        Baoquan He <bhe@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
        linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less
 confusion

Trying one more time; sorry (again) if someone receives this in duplicate.

>>>
>>> diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
>>> index 56cab1bb25f5..085eef5c3904 100644
>>> --- a/arch/x86/kernel/relocate_kernel_64.S
>>> +++ b/arch/x86/kernel/relocate_kernel_64.S
>>> @@ -148,9 +148,10 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
>>>    	 */
>>>    	movl	$X86_CR4_PAE, %eax
>>>    	testq	$X86_CR4_LA57, %r13
>>> -	jz	1f
>>> +	jz	.Lno_la57
>>>    	orl	$X86_CR4_LA57, %eax
>>> -1:
>>> +.Lno_la57:
>>> +
>>>    	movq	%rax, %cr4

If we are cleaning up this code... the above can simply be:

	andl $(X86_CR4_PAE | X86_CR4_LA54), %r13
	movq %r13, %cr4

%r13 is dead afterwards, and the PAE bit *will* be set in %r13 anyway.

	-hpa