linux-kernel - Re: [PATCH 2/9] x86/kexec: Ensure preserve_context flag is set on return to kernel

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Message-ID: <4b077c6045a5317a3925e42fb1b8557cbbb41745.camel@infradead.org>
Date: Fri, 03 Jan 2025 10:14:38 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Uros Bizjak <ubizjak@...il.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>, Eric Biederman <ebiederm@...ssion.com>, Sourabh Jain
 <sourabhjain@...ux.ibm.com>, Hari Bathini <hbathini@...ux.ibm.com>, Michael
 Ellerman <mpe@...erman.id.au>, Thomas Zimmermann <tzimmermann@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>, 
 Yuntao Wang <ytcoode@...il.com>, David Kaplan <david.kaplan@....com>, Tao
 Liu <ltao@...hat.com>, "Kirill A. Shutemov"
 <kirill.shutemov@...ux.intel.com>, Kai Huang <kai.huang@...el.com>, Ard
 Biesheuvel <ardb@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, Breno
 Leitao <leitao@...ian.org>, Wei Yang <richard.weiyang@...il.com>, Rong Xu
 <xur@...gle.com>, Thomas Weißschuh
 <thomas.weissschuh@...utronix.de>, linux-kernel@...r.kernel.org, 
 kexec@...ts.infradead.org, Simon Horman <horms@...nel.org>, Dave Young
 <dyoung@...hat.com>, Peter Zijlstra <peterz@...radead.org>, bsz@...zon.de, 
 nathan@...nel.org
Subject: Re: [PATCH 2/9] x86/kexec: Ensure preserve_context flag is set on
 return to kernel

On Tue, 2024-12-17 at 17:38 +0100, Uros Bizjak wrote:
>  
> > diff --git a/arch/x86/kernel/relocate_kernel_64.S
> > b/arch/x86/kernel/relocate_kernel_64.S
> > index 9bd601dd8659..1a52e4339c1d 100644
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -220,6 +220,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> >    	movq	kexec_pa_table_page(%rip), %rax
> >    	movq	%rax, %cr3
> >    	lea	PAGE_SIZE(%r8), %rsp
> > +	movq	$1, %r11	/* Ensure preserve_context flag is
> > set */
> 
> You can save a byte here by using "movl $1, %r11d".

Thanks. I've done that locally.

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