Re: [Xen-devel] [Patch V2 1/2] xen: prepare p2m list for memory hotplug

[David Vrabel <david.vrabel@citrix.com>]

On 20/03/15 12:55, Juergen Gross wrote:
> Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
> virtual mapped sparse p2m list") introduced a regression regarding to
> memory hotplug for a pv-domain: as the virtual space for the p2m list
> is allocated for the to be expected memory size of the domain only,
> hotplugged memory above that size will not be usable by the domain.
> 
> Correct this by using a configurable size for the p2m list in case of
> memory hotplug enabled (default supported memory size is 512 GB for
> 64 bit domains and 4 GB for 32 bit domains).
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  arch/x86/xen/p2m.c  | 10 +++++++++-
>  drivers/xen/Kconfig | 14 ++++++++++++++
>  2 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 9f93af5..b47124d 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -91,6 +91,12 @@ EXPORT_SYMBOL_GPL(xen_p2m_size);
>  unsigned long xen_max_p2m_pfn __read_mostly;
>  EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);
>  
> +#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> +#define P2M_LIMIT CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> +#else
> +#define P2M_LIMIT 0
> +#endif
> +
>  static DEFINE_SPINLOCK(p2m_update_lock);
>  
>  static unsigned long *p2m_mid_missing_mfn;
> @@ -385,9 +391,11 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m)
>  void __init xen_vmalloc_p2m_tree(void)
>  {
>  	static struct vm_struct vm;
> +	unsigned long p2m_limit;
>  
> +	p2m_limit = (phys_addr_t)P2M_LIMIT * 1024 * 1024 * 1024 / PAGE_SIZE;
>  	vm.flags = VM_ALLOC;
> -	vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
> +	vm.size = ALIGN(sizeof(unsigned long) * max(xen_max_p2m_pfn, p2m_limit),
>  			PMD_SIZE * PMDS_PER_MID_PAGE);
>  	vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
>  	pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index b812462..0f1b509 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -55,6 +55,20 @@ config XEN_BALLOON_MEMORY_HOTPLUG
>  
>  	  In that case step 3 should be omitted.
>  
> +config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> +	int

Because you've not supplied a summary for this option, it is not user
configurable.  Is this intentional?

David