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

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Message-ID: <ZS/RsVFDFImuHDJC@gmail.com>
Date:   Wed, 18 Oct 2023 14:38:09 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kalra, Ashish" <ashish.kalra@....com>
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.


* Kalra, Ashish <ashish.kalra@....com> wrote:

> 
> 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.

Please integrate the information I suggested into the changelog and submit 
a v2 patch.

Thanks,

	Ingo