linux-kernel - Re: [RFC, PATCH 18/22] x86/mm: Handle allocation of encrypted pages

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Date:   Tue, 6 Mar 2018 11:34:25 +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>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC, PATCH 18/22] x86/mm: Handle allocation of encrypted pages

On Mon, Mar 05, 2018 at 11:03:55AM -0800, Dave Hansen wrote:
> On 03/05/2018 08:26 AM, Kirill A. Shutemov wrote:
> > -#define __alloc_zeroed_user_highpage(movableflags, vma, vaddr) \
> > -	alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO | movableflags, vma, vaddr)
> >  #define __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE
> > +#define __alloc_zeroed_user_highpage(movableflags, vma, vaddr)			\
> > +({										\
> > +	struct page *page;							\
> > +	gfp_t gfp = movableflags | GFP_HIGHUSER;				\
> > +	if (vma_is_encrypted(vma))						\
> > +		page = __alloc_zeroed_encrypted_user_highpage(gfp, vma, vaddr);	\
> > +	else									\
> > +		page = alloc_page_vma(gfp | __GFP_ZERO, vma, vaddr);		\
> > +	page;									\
> > +})
> 
> This is pretty darn ugly and also adds a big old branch into the hottest
> path in the page allocator.
> 
> It's also really odd that you strip __GFP_ZERO and then go ahead and
> zero the encrypted page unconditionally.  It really makes me wonder if
> this is the right spot to be doing this.
> 
> Can we not, for instance do it inside alloc_page_vma()?

Yes we can.

It would require substantial change into page allocation path for
CONFIG_NUMA=n as we don't path down vma at the moment. And without vma we
don't have a way to know which KeyID to use.

I will explore how it would fit together.

-- 
 Kirill A. Shutemov