linux-kernel - Re: [PATCHv10 09/18] x86/mm: Adding callbacks to prepare encrypted memory for kexec

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Date: Sat, 27 Apr 2024 18:47:47 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"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>, Baoquan He <bhe@...hat.com>,
	kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Nikolay Borisov <nik.borisov@...e.com>, Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv10 09/18] x86/mm: Adding callbacks to prepare encrypted
 memory for kexec

On Tue, Apr 09, 2024 at 02:30:01PM +0300, Kirill A. Shutemov wrote:
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index e74d0c4286c1..7a1560d7e62d 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -128,6 +128,12 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>  #ifdef CONFIG_HPET_TIMER
>  	hpet_disable();
>  #endif
> +
> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> +		x86_platform.guest.enc_kexec_stop_conversion(true);
> +		x86_platform.guest.enc_kexec_unshare_mem();
> +	}

This is not how this is done - the point of those function pointers is
to avoid random checks in the code but simply unconditionally call them.

The platform which needs something special to happen, assigns to them
its own function pointers and the rest assigns dummy stubs.

-- 
Regards/Gruss,
    Boris.

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