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

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Message-ID: <ad4c704f-fdda-7e75-60ec-3fbc8a4bb0ba@intel.com>
Date:   Wed, 18 Jul 2018 16:11:57 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "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>
Cc:     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 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.


> 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.