linux-kernel - Re: [PATCH] x86/mm: fix pg_level_to

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Message-ID: <f7aa58e0-7fcd-35a9-d04c-1369a8cb0701@amd.com>
Date:   Mon, 16 Oct 2023 13:32:04 -0500
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        thomas.lendacky@....com, linux-kernel@...r.kernel.org,
        peterz@...radead.org
Subject: Re: [PATCH] x86/mm: fix pg_level_to_pfn for 5-level paging mode.


On 10/14/2023 3:47 AM, Ingo Molnar wrote:
> 
> * Ashish Kalra <Ashish.Kalra@....com> wrote:
> 
>> From: Ashish Kalra <ashish.kalra@....com>
>>
>> Add support for 5-level paging in pg_level_to_pfn().
>>
>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>> ---
>>   arch/x86/mm/mem_encrypt_amd.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
>> index 6faea41e99b6..45914568596a 100644
>> --- a/arch/x86/mm/mem_encrypt_amd.c
>> +++ b/arch/x86/mm/mem_encrypt_amd.c
>> @@ -267,6 +267,10 @@ static unsigned long pg_level_to_pfn(int level, pte_t *kpte, pgprot_t *ret_prot)
>>   		pfn = pud_pfn(*(pud_t *)kpte);
>>   		prot = pud_pgprot(*(pud_t *)kpte);
>>   		break;
>> +	case PG_LEVEL_512G:
>> +		pfn = p4d_pfn(*(p4d_t *)kpte);
>> +		prot = p4d_pgprot(*(p4d_t *)kpte);
>> +		break;
> 
> Mind explaining what happens if we don't have this fix, how you found it,
> which users are expected to be affected by it, whether that's the full
> known extent of 5-level paging support deficiencies in mem_encrypt_amd.c,foud 
> etc?
>

It was found during working on SNP guest kexec support, this helper 
function is used during early boot stage for setting of C-bit on the 
PTEs and additionally need this same helper for switching shared pages 
to private during guest kexec, so i believe this patch is needed.

Thanks,
Ashish

> In addition to such patches being much easier on the eyes, it also helps
> maintainers prioritize patches.
> 
> Thanks,
> 
> 	Ingo
>