Re: [PATCH] x86: Convert shadow-paging to Kconfig

From: Ian Campbell <ian.campbell@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Xen-devel <xen-devel@lists.xen.org>
Cc: George Dunlap <george.dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>, Doug Goldstein <cardoe@cardoe.com>,
	Jan Beulich <JBeulich@suse.com>
Subject: Re: [PATCH] x86: Convert shadow-paging to Kconfig
Date: Tue, 19 Jan 2016 09:46:36 +0000	[thread overview]
Message-ID: <1453196796.6020.217.camel@citrix.com> (raw)
In-Reply-To: <1453142404-8819-1-git-send-email-andrew.cooper3@citrix.com>

On Mon, 2016-01-18 at 18:40 +0000, Andrew Cooper wrote:
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Does this have any impact on migration of either PV or HVM guests? What
about nested virt?

Are things which are defined in xen/arch/*/Rules.mk in this way
overrideable from the old top-level .config or does one need to dive deeper
to modify them? If it's not configurable from top-level .config today then
I think it either needs a "depends EXPERT" or for the changelog to make a
convincing argument why this should be made user selectable.

Lastly, Tim is maintainer of the shadow code and should have been CC-d,
also George as maintainer of the mm stuff might have an interest. Both CC-s 
added.

> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Doug Goldstein <cardoe@cardoe.com>
> ---
>  xen/arch/x86/Kconfig            | 14 ++++++++++++++
>  xen/arch/x86/Rules.mk           |  4 ----
>  xen/arch/x86/mm/shadow/Makefile |  2 +-
>  3 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> index 4781b34..9869630 100644
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -27,6 +27,20 @@ menu "Architecture Features"
>  
>  source "arch/Kconfig"
>  
> +config SHADOW_PAGING
> +        bool "Shadow Paging"
> +        default y
> +        ---help---
> +          Shadow paging is a software alternative to hardware paging
> support
> +          (Intel EPT, AMD NPT) for use with HVM guests.
> +
> +          It is required to run HVM guests for first-generation hardware
> +          virtualisation (Intel VT-x, AMD SVM) which did not include
> hardware
> +          paging support.  Under a small number of specific workloads,
> shadow
> +          paging may also be deliberately used as a performance
> improvement.
> +
> +          If unsure, say Y.
> +
>  config BIGMEM
>  	bool "big memory support"
>  	default n
> diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
> index a108d24..a1cdae0 100644
> --- a/xen/arch/x86/Rules.mk
> +++ b/xen/arch/x86/Rules.mk
> @@ -22,13 +22,9 @@ $(call as-insn-check,CFLAGS,CC,".equ \"x\"$$(comma)1",
> \
>                       -U__OBJECT_LABEL__ -DHAVE_GAS_QUOTED_SYM \
>                       '-D__OBJECT_LABEL__=$(subst
> $(BASEDIR)/,,$(CURDIR))/$$@')
>  
> -shadow-paging ?= y
> -
>  CFLAGS += -mno-red-zone -mno-sse -fpic
>  CFLAGS += -fno-asynchronous-unwind-tables
>  # -fvisibility=hidden reduces -fpic cost, if it's available
>  ifneq ($(call cc-option,$(CC),-fvisibility=hidden,n),n)
>  CFLAGS += -DGCC_HAS_VISIBILITY_ATTRIBUTE
>  endif
> -
> -CFLAGS-$(shadow-paging) += -DCONFIG_SHADOW_PAGING
> diff --git a/xen/arch/x86/mm/shadow/Makefile
> b/xen/arch/x86/mm/shadow/Makefile
> index a07bc0c..df194ad 100644
> --- a/xen/arch/x86/mm/shadow/Makefile
> +++ b/xen/arch/x86/mm/shadow/Makefile
> @@ -1,4 +1,4 @@
> -ifeq ($(shadow-paging),y)
> +ifdef CONFIG_SHADOW_PAGING
>  obj-y += common.o guest_2.o guest_3.o guest_4.o
>  else
>  obj-y += none.o

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