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

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Date: Mon, 5 Feb 2024 14:49:10 +0800
From: "Huang, Kai" <kai.huang@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>
CC: <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 2/02/2024 12:57 am, Dave Hansen wrote:
> On 2/1/24 06:39, Kirill A. Shutemov 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
> ...
>> +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);
> 
> It's a little funky that we've got a #ifdef CONFIG_KEXEC_JUMP in the .c
> file and then we're dodging around an #ifdef CONFIG_PM_SLEEP in the
> header.  This is one of the reasons we shouldn't be putting #ifdefs in
> .c files in the first place.  But I digress...
> 
> Either way, if you focus on getting the dang #ifdef out of the main code
> flow, the rest will fall in place easily.  Heck, if you even do this in
> the x86 kexec code:
> 
> static void kexec_save_processor_start(image)
> {
> #ifdef CONFIG_KEXEC_JUMP
> 	if (image->preserve_context)
> 		save_processor_state();
> #endif
> }
> 
> it'll leave you with:
> 
> 	kexec_save_processor_start(image);
> 
> 	/* Give a good reason here */
> 	if (!image->preserve_context)
> 		tdx_reset_memory();
> 
> which is *FINE*.  No funky #ifdefs, indentation or else's dangling about.
> 
> 

Thanks for the insight and explanation!  I'll use this in the new version.