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

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Date:   Mon, 5 Mar 2018 11:03:55 -0800
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>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC, PATCH 18/22] x86/mm: Handle allocation of encrypted pages

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()?