linux-kernel - Re: [PATCHv5 06/19] mm/khugepaged: Handle encrypted pages

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Message-ID: <20180719085901.ebdciqkjpx6hy4xt@kshutemo-mobl1>
Date:   Thu, 19 Jul 2018 11:59:01 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 06/19] mm/khugepaged: Handle encrypted pages

On Wed, Jul 18, 2018 at 04:11:57PM -0700, Dave Hansen wrote:
> On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> > khugepaged allocates page in advance, before we found a VMA for
> > collapse. We don't yet know which KeyID to use for the allocation.
> 
> That's not really true.  We have the VMA and the address in the caller
> (khugepaged_scan_pmd()), but we drop the lock and have to revalidate the
> VMA.

For !NUMA we allocate the page in khugepaged_do_scan(), well before we
know VMA.

> 
> 
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 5ae34097aed1..d116f4ebb622 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -1056,6 +1056,16 @@ static void collapse_huge_page(struct mm_struct *mm,
> >  	 */
> >  	anon_vma_unlock_write(vma->anon_vma);
> >  
> > +	/*
> > +	 * At this point new_page is allocated as non-encrypted.
> > +	 * If VMA's KeyID is non-zero, we need to prepare it to be encrypted
> > +	 * before coping data.
> > +	 */
> > +	if (vma_keyid(vma)) {
> > +		prep_encrypted_page(new_page, HPAGE_PMD_ORDER,
> > +				vma_keyid(vma), false);
> > +	}
> 
> I guess this isn't horribly problematic now, but if we ever keep pools
> of preassigned-keyids, this won't work any more.

I don't get this. What pools of preassigned-keyids are you talking about?

-- 
 Kirill A. Shutemov