linux-kernel - RE: [PATCH v6 2/5] x86/kexec: do unconditional WBINVD for bare-metal in relocate

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Message-ID:
 <LV3PR12MB9265900A6564C22E9F6666ED949A2@LV3PR12MB9265.namprd12.prod.outlook.com>
Date: Tue, 10 Sep 2024 02:46:07 +0000
From: "Kaplan, David" <David.Kaplan@....com>
To: "Huang, Kai" <kai.huang@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "bp@...en8.de" <bp@...en8.de>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>, "hpa@...or.com" <hpa@...or.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
CC: "x86@...nel.org" <x86@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "Williams, Dan J"
	<dan.j.williams@...el.com>, "Lendacky, Thomas" <Thomas.Lendacky@....com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "Kalra, Ashish" <Ashish.Kalra@....com>,
	"bhe@...hat.com" <bhe@...hat.com>, "nik.borisov@...e.com"
	<nik.borisov@...e.com>, "sagis@...gle.com" <sagis@...gle.com>, Dave Young
	<dyoung@...hat.com>
Subject: RE: [PATCH v6 2/5] x86/kexec: do unconditional WBINVD for bare-metal
 in relocate_kernel()

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Huang, Kai <kai.huang@...el.com>
> Sent: Monday, September 9, 2024 9:42 PM
> To: Kaplan, David <David.Kaplan@....com>; Hansen, Dave
> <dave.hansen@...el.com>; bp@...en8.de; tglx@...utronix.de;
> peterz@...radead.org; mingo@...hat.com; hpa@...or.com;
> kirill.shutemov@...ux.intel.com
> Cc: x86@...nel.org; linux-kernel@...r.kernel.org; pbonzini@...hat.com;
> seanjc@...gle.com; Williams, Dan J <dan.j.williams@...el.com>; Lendacky,
> Thomas <Thomas.Lendacky@....com>; Edgecombe, Rick P
> <rick.p.edgecombe@...el.com>; Yamahata, Isaku
> <isaku.yamahata@...el.com>; Kalra, Ashish <Ashish.Kalra@....com>;
> bhe@...hat.com; nik.borisov@...e.com; sagis@...gle.com; Dave Young
> <dyoung@...hat.com>
> Subject: Re: [PATCH v6 2/5] x86/kexec: do unconditional WBINVD for bare-
> metal in relocate_kernel()
>
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
>
>
> >> --- a/arch/x86/kernel/machine_kexec_64.c
> >> +++ b/arch/x86/kernel/machine_kexec_64.c
> >> @@ -322,16 +322,9 @@ void machine_kexec_cleanup(struct kimage
> *image)
> >> void machine_kexec(struct kimage *image)  {
> >>          unsigned long page_list[PAGES_NR];
> >> -       unsigned int host_mem_enc_active;
> >>          int save_ftrace_enabled;
> >>          void *control_page;
> >>
> >> -       /*
> >> -        * This must be done before load_segments() since if call depth
> tracking
> >> -        * is used then GS must be valid to make any function calls.
> >> -        */
> >> -       host_mem_enc_active =
> >> cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT);
> >> -
> >
> > Functionally the patch looks fine.  I would suggest keeping some form of
> this comment though, because the limitation about not being able to make
> function calls after load_segments() is arguably non-obvious and this
> comment served as a warning for future modifications in this area.
>
> Yeah this makes sense.  Thanks.
>
> I think we can add some text to the existing comment of load_segments() to
> call out this.  Allow me to dig into more about call depth tracking to
> understand it better -- relocate_kernel() after load_segments() seems to be a
> real function call and I want to know how does it interact with call depth
> tracking.

That one is explicitly ignored, see skip_addr() in arch/x86/kernel/callthunks.c

--David Kaplan