linux-kernel - Re: [PATCH 3/4] x86/kexec(): Reset TDX private memory on platforms with TDX erratum

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Date: Thu, 1 Feb 2024 16:39:00 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: Dave Hansen <dave.hansen@...el.com>, linux-kernel@...r.kernel.org, 
	x86@...nel.org, tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, 
	hpa@...or.com, luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com, 
	chao.gao@...el.com, bhe@...hat.com, nik.borisov@...e.com, pbonzini@...hat.com
Subject: Re: [PATCH 3/4] x86/kexec(): Reset TDX private memory on platforms
 with TDX erratum

On Thu, Feb 01, 2024 at 10:22:18PM +0800, Huang, Kai wrote:
> 
> 
> On 1/02/2024 6:03 am, Kirill A. Shutemov wrote:
> > On Wed, Jan 31, 2024 at 01:21:39PM -0800, Dave Hansen wrote:
> > > >   #ifdef CONFIG_KEXEC_JUMP
> > > >   	if (image->preserve_context)
> > > >   		save_processor_state();
> > > > +	else
> > > > +		tdx_reset_memory();
> > > > +#else
> > > > +	tdx_reset_memory();
> > > >   #endif
> > > 
> > > Wow, that's awfully hard to read.  I really wish folks' gag reflex would
> > > kick in when they see stuff like this to get them to spend an additional
> > > 15 seconds to turn this into:
> > > 
> > > 	if (IS_ENABLED(CONFIG_KEXEC_JUMP) && image->preserve_context)
> > > 		save_processor_state();
> > > 	else
> > > 		tdx_reset_memory();
> > 
> > save_processor_state() is declared under CONFIG_PM_SLEEP, so I guess your
> > variant might break build in some cases without updated suspend.h.
> 
> I tried.  If I turn off both SUSPEND and HIBERNATION in the Kconfig I got
> build error：
> 
> arch/x86/kernel/machine_kexec_64.c:325:17: error: implicit declaration of
> function ‘save_processor_state’ [-Werror=implicit-function-declaration]
>   325 |                 save_processor_state();
>       |                 ^~~~~~~~~~~~~~~~~~~~

Moving save_processor_state() declaration outside all defines would do the
trick.

Something like the patch below.

But finding the right spot for the move can be tricky. I don't particular
like where I moved it.

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index ef503088942d..1c17059df039 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -201,6 +201,9 @@ struct platform_s2idle_ops {
 	void (*end)(void);
 };
 
+void save_processor_state(void);
+void restore_processor_state(void);
+
 #ifdef CONFIG_SUSPEND
 extern suspend_state_t pm_suspend_target_state;
 extern suspend_state_t mem_sleep_current;
@@ -491,8 +494,6 @@ static inline int is_hibernate_resume_dev(dev_t dev) { return 0; }
 extern struct mutex system_transition_mutex;
 
 #ifdef CONFIG_PM_SLEEP
-void save_processor_state(void);
-void restore_processor_state(void);
 
 /* kernel/power/main.c */
 extern int register_pm_notifier(struct notifier_block *nb);
-- 
  Kiryl Shutsemau / Kirill A. Shutemov