linux-kernel - Re: [PATCH 7/8] x86: Enable 5-level paging support

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Message-ID: <469e1232-617c-daaa-90a6-a90d6f80059f@suse.com>
Date:   Thu, 6 Apr 2017 16:52:11 +0200
From:   Juergen Gross <jgross@...e.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] x86: Enable 5-level paging support

On 06/04/17 16:01, Kirill A. Shutemov wrote:
> Most of things are in place and we can enable support of 5-level paging.
> 
> Enabling XEN with 5-level paging requires more work. The patch makes XEN
> dependent on !X86_5LEVEL.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/Kconfig     | 5 +++++
>  arch/x86/xen/Kconfig | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 4e153e93273f..7a76dcac357e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -318,6 +318,7 @@ config FIX_EARLYCON_MEM
>  
>  config PGTABLE_LEVELS
>  	int
> +	default 5 if X86_5LEVEL
>  	default 4 if X86_64
>  	default 3 if X86_PAE
>  	default 2
> @@ -1390,6 +1391,10 @@ config X86_PAE
>  	  has the cost of more pagetable lookup overhead, and also
>  	  consumes more pagetable space per process.
>  
> +config X86_5LEVEL
> +	bool "Enable 5-level page tables support"
> +	depends on X86_64
> +
>  config ARCH_PHYS_ADDR_T_64BIT
>  	def_bool y
>  	depends on X86_64 || X86_PAE
> diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
> index 76b6dbd627df..b90d481ce5a1 100644
> --- a/arch/x86/xen/Kconfig
> +++ b/arch/x86/xen/Kconfig
> @@ -5,6 +5,7 @@
>  config XEN
>  	bool "Xen guest support"
>  	depends on PARAVIRT
> +	depends on !X86_5LEVEL
>  	select PARAVIRT_CLOCK
>  	select XEN_HAVE_PVMMU
>  	select XEN_HAVE_VPMU
> 

Just a heads up: this last change will conflict with the Xen tree.

Can't we just ignore the additional level in Xen pv mode and run with
4 levels instead?


Juergen