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 22:47:41 +0800
From: "Huang, Kai" <kai.huang@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 1/02/2024 10:39 pm, Kirill A. Shutemov wrote:
> 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.
> 

I don't feel I have enough justification to do such change.

As I replied in another email, how about:

#ifdef CONFIG_KEXEC_JUMP
     if (image->preserve_context)
         save_processor_state();
     else
#endif
     tdx_reset_memory();

Not ideal, but looks slightly better?

But I'll leave to Dave to comment.