linux-kernel - Re: [PATCH v5 1/7] x86/kexec: Consolidate relocate

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Message-ID: <f900255ba4ea57cc2095790c2d14b0bcb3487da1.camel@intel.com>
Date: Wed, 6 Aug 2025 22:29:19 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "thomas.lendacky@....com" <thomas.lendacky@....com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com"
	<hpa@...or.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "Edgecombe, Rick P"
	<rick.p.edgecombe@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>, "kas@...nel.org" <kas@...nel.org>,
	"sagis@...gle.com" <sagis@...gle.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Williams, Dan J" <dan.j.williams@...el.com>,
	"nik.borisov@...e.com" <nik.borisov@...e.com>, "ashish.kalra@....com"
	<ashish.kalra@....com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"dwmw@...zon.co.uk" <dwmw@...zon.co.uk>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v5 1/7] x86/kexec: Consolidate relocate_kernel() function
 parameters

On Wed, 2025-08-06 at 08:00 -0500, Tom Lendacky wrote:
> On 8/6/25 01:53, Huang, Kai wrote:
> > On Tue, 2025-07-29 at 00:28 +1200, Kai Huang wrote:
> > > During kexec, the kernel jumps to the new kernel in relocate_kernel(),
> > > which is implemented in assembly and both 32-bit and 64-bit have their
> > > own version.
> > > 
> > > Currently, for both 32-bit and 64-bit, the last two parameters of the
> > > relocate_kernel() are both 'unsigned int' but actually they only convey
> > > a boolean, i.e., one bit information.  The 'unsigned int' has enough
> > > space to carry two bits information therefore there's no need to pass
> > > the two booleans in two separate 'unsigned int'.
> > > 
> > > Consolidate the last two function parameters of relocate_kernel() into a
> > > single 'unsigned int' and pass flags instead.
> > > 
> > > Only consolidate the 64-bit version albeit the similar optimization can
> > > be done for the 32-bit version too.  Don't bother changing the 32-bit
> > > version while it is working (since assembly code change is required).
> > > 
> > > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > > ---
> > > 
> > >  v4 -> v5:
> > >   - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
> > >     (Tom)
> > >   - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
> > >     restored after jumping back from peer kernel for preserved_context
> > >     kexec (pointed out by Tom).
> > >   - Use testb instead of testq when comparing the flag with R11 to save
> > >     3 bytes (Hpa).
> > > 
> > > 
> > 
> > Hi Tom,
> > 
> > Wondering do you have more comments?  Thanks.
> 
> Sorry for the delay, LGTM.
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

Thanks Tom!

(It should be me to thank you so don't be sorry. :-))