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

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Message-ID: <2b661d91-badc-4c90-9a9a-fe82635cf514@zytor.com>
Date: Mon, 3 Jun 2024 15:43:41 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Nikolay Borisov <nik.borisov@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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
Cc: "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

On 5/29/24 03:47, Nikolay Borisov wrote:
>>
>> 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
>>       jmp 1f
> 

Sorry if this is a duplicate; something strange happened with my email.

If you are cleaning up this code anyway...

this whole piece of code can be simplified to:

	and $(X86_CR4_PAE | X86_CR4_LA57), %r13d
	mov %r13, %cr4

The PAE bit in %r13 is guaranteed to be set, and %r13 is dead after this.

	-hpa