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Date: Wed, 18 Feb 2015 10:21:32 +0100
From: Paul Bolle <pebolle@...cali.nl>
To: Juergen Gross <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
konrad.wilk@...cle.com, david.vrabel@...rix.com,
boris.ostrovsky@...cle.com
Subject: Re: [PATCH 13/13] xen: allow more than 512 GB of RAM for 64 bit
pv-domains
On Wed, 2015-02-18 at 07:52 +0100, Juergen Gross wrote:
> 64 bit pv-domains under Xen are limited to 512 GB of RAM today. The
> main reason has been the 3 level p2m tree, which was replaced by the
> virtual mapped linear p2m list. Parallel to the p2m list which is
> being used by the kernel itself there is a 3 level mfn tree for usage
> by the Xen tools and eventually for crash dump analysis. For this tree
> the linear p2m list can serve as a replacement, too. As the kernel
> can't know whether the tools are capable of dealing with the p2m list
> instead of the mfn tree, the limit of 512 GB can't be dropped in all
> cases.
>
> This patch replaces the hard limit by a kernel parameter which tells
> the kernel to obey the 512 GB limit or not. The default is selected by
> a configuration parameter which specifies whether the 512 GB limit
> should be active per default for dom0 (only crash dump analysis is
> affected) and/or for domUs (additionally domain save/restore/migration
> are affected).
>
> Memory above the domain limit is returned to the hypervisor instead of
> being identity mapped, which was wrong anyways.
>
> The kernel configuration parameter to specify the maximum size of a
> domain can be deleted, as it is not relevant any more.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> Documentation/kernel-parameters.txt | 7 ++++
> arch/x86/include/asm/xen/page.h | 4 ---
> arch/x86/xen/Kconfig | 31 +++++++++++-----
> arch/x86/xen/p2m.c | 10 +++---
> arch/x86/xen/setup.c | 72 ++++++++++++++++++++++++++++++-------
> 5 files changed, 93 insertions(+), 31 deletions(-)
[...]
> --- a/arch/x86/xen/Kconfig
> +++ b/arch/x86/xen/Kconfig
> @@ -23,14 +23,29 @@ config XEN_PVHVM
> def_bool y
> depends on XEN && PCI && X86_LOCAL_APIC
>
> -config XEN_MAX_DOMAIN_MEMORY
> - int
> - default 500 if X86_64
> - default 64 if X86_32
> - depends on XEN
> - help
> - This only affects the sizing of some bss arrays, the unused
> - portions of which are freed.
> +if X86_64
Not
&& XEN
?
> +choice
> + prompt "Support pv-domains larger than 512GB"
> + default XEN_512GB_NONE
> + help
> + Support paravirtualized domains with more than 512GB of RAM.
> +
> + The Xen tools and crash dump analysis tools might not support
> + pv-domains with more than 512 GB of RAM. This option controls the
> + default setting of the kernel to use only up to 512 GB or more.
> + It is always possible to change the default via specifying the
> + boot parameter "xen_512gb_limit".
> +
> + config XEN_512GB_NONE
> + bool "neither dom0 nor domUs can be larger than 512GB"
> + config XEN_512GB_DOM0
> + bool "dom0 can be larger than 512GB, domUs not"
> + config XEN_512GB_DOMU
> + bool "domUs can be larger than 512GB, dom0 not"
> + config XEN_512GB_ALL
> + bool "dom0 and domUs can be larger than 512GB"
> +endchoice
So there are actually two independent limits, configured through a
choice with four entries. Would using just two separate Kconfig symbols
(XEN_512GB_DOM0 and XEN_512GB_DOMU) without a choice wrapper also work?
Because ...
> +endif
>
> config XEN_SAVE_RESTORE
> bool
[...]
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 84a6473..16d94de 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -32,6 +32,8 @@
> #include "p2m.h"
> #include "mmu.h"
>
> +#define GB(x) ((uint64_t)(x) * 1024 * 1024 * 1024)
> +
> /* Amount of extra memory space we add to the e820 ranges */
> struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
>
> @@ -85,6 +87,27 @@ static struct {
> */
> #define EXTRA_MEM_RATIO (10)
>
> +static bool xen_dom0_512gb_limit __initdata =
> + IS_ENABLED(CONFIG_XEN_512GB_NONE) || IS_ENABLED(CONFIG_XEN_512GB_DOMU);
... then this could be something like:
static bool xen_dom0_512gb_limit __initdata = !IS_ENABLED(CONFIG_XEN_512GB_DOM0);
> +static bool xen_domu_512gb_limit __initdata =
> + IS_ENABLED(CONFIG_XEN_512GB_NONE) || IS_ENABLED(CONFIG_XEN_512GB_DOM0);
> +
and this likewise:
static bool xen_domu_512gb_limit __initdata = !IS_ENABLED(CONFIG_XEN_512GB_DOMU);
Correct?
> +static int __init xen_parse_512gb(char *arg)
> +{
> + bool val = false;
> +
> + if (!arg)
> + val = true;
> + else if (strtobool(arg, &val))
> + return 1;
> +
> + xen_dom0_512gb_limit = val;
> + xen_domu_512gb_limit = val;
> +
> + return 0;
> +}
> +early_param("xen_512gb_limit", xen_parse_512gb);
> +
> static void __init xen_add_extra_mem(phys_addr_t start, phys_addr_t size)
> {
> int i;
So one can configure these two limits separately, but the kernel
parameter is used for both. Any particular reason?
Thanks,
Paul Bolle
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