linux-kernel - Re: [PATCH v9 3/3] x86/snp: Convert shared memory back to private on kexec

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Date: Fri, 28 Jun 2024 15:33:00 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 x86@...nel.org, rafael@...nel.org, hpa@...or.com, peterz@...radead.org,
 adrian.hunter@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 jun.nakajima@...el.com, rick.p.edgecombe@...el.com, thomas.lendacky@....com,
 michael.roth@....com, seanjc@...gle.com, kai.huang@...el.com,
 bhe@...hat.com, kirill.shutemov@...ux.intel.com, bdas@...hat.com,
 vkuznets@...hat.com, dionnaglaze@...gle.com, anisinha@...hat.com,
 jroedel@...e.de, ardb@...nel.org, dyoung@...hat.com,
 kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 3/3] x86/snp: Convert shared memory back to private on
 kexec


On 6/24/2024 1:26 PM, Borislav Petkov wrote:
>> +	 */
>> +
>> +	addr = PAGE_OFFSET;
>> +	end  = PAGE_OFFSET + get_max_mapped();
>> +
>> +	while (addr < end) {
>> +		unsigned long size;
>> +		unsigned int level;
>> +		pte_t *pte;
>> +
>> +		pte = lookup_address(addr, &level);
>> +		size = page_level_size(level);
>> +
>> +		/*
>> +		 * pte_none() check is required to skip physical memory holes in direct mapped.
> This sentence needs to be written for humans. And come to think of it, you can
> simply drop it. lookup_address() can return NULL so you simply need to check
> its retval.
I had to additionally add check for pte_none() here to handle physical memory holes in direct mapping.

Looking at lookup_address_in_pgd_attr(), at pte level it is simply returning pte_offset_kernel() and there does not seem to be a check for returning NULL if pte_none() ?

Probably need to fix lookup_address_in_pgd_attr(), to add check for pte_none() after pte_offset_kernel() and return NULL if it is true.

Thanks, Ashish

>> +		 */
>> +		if (pte && pte_decrypted(*pte) && !pte_none(*pte)) {
>> +			int pages = size / PAGE_SIZE;
>>