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Date: Tue, 4 Jun 2024 11:15:03 +0200
From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Nikolay Borisov <nik.borisov@suse.com>,
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	Peter Zijlstra <peterz@infradead.org>,
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Subject: Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less
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On Mon, Jun 03, 2024 at 05:24:00PM -0700, H. Peter Anvin wrote:
> 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.

Yeah, with a proper comment. The testing of bits is not really needed.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette