linux-kernel - Re: [PATCHv11 11/19] x86/tdx: Convert shared memory back to private on kexec

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Date: Fri, 31 May 2024 12:34:49 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Borislav Petkov <bp@...en8.de>,
 "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>,
 Sean Christopherson <seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>,
 Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
 "H. Peter Anvin" <hpa@...or.com>, "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
 linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv11 11/19] x86/tdx: Convert shared memory back to private
 on kexec

Hello Boris,

On 5/31/2024 10:14 AM, Borislav Petkov wrote:
>>   static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
>>   {
>> -	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
>> -		return __set_memory_enc_pgtable(addr, numpages, enc);
>> +	int ret = 0;
>>   
>> -	return 0;
>> +	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
>> +		if (!down_read_trylock(&mem_enc_lock))
>> +			return -EBUSY;
>> +
>> +		ret = __set_memory_enc_pgtable(addr, numpages, enc);
>> +
>> +		up_read(&mem_enc_lock);
>> +	}
> So CC_ATTR_MEM_ENCRYPT is set for SEV* guests too. You need to change
> that code here to take the lock only on TDX, where you want it, not on
> the others.

SNP guest kexec patches are based on top of this patch-series and SNP 
guests also need this exclusive mem_enc_lock protection, so 
CC_ATTR_MEM_ENCRYPT makes sense to be used here.

Thanks, Ashish