Re: [Xen-devel] [PATCH 2/2] xen: before ballooning hotplugged memory, set frames to invalid

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Thu, Mar 19, 2015 at 03:31:02PM +0100, Juergen Gross wrote:
> Commit 25b884a83d487fd62c3de7ac1ab5549979188482 ("x86/xen: set
> regions above the end of RAM as 1:1") introduced a regression.
>
> To be able to add memory pages which were added via memory hotplug to
> a pv domain, the pages must be "invalid" instead of "identity" in the
> p2m list before they can be added.
>
> Suggested-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  drivers/xen/balloon.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 0b52d92..52e331f 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -221,15 +221,24 @@ static bool balloon_is_inflated(void)
>
>  static enum bp_state reserve_additional_memory(long credit)
>  {
> -     int nid, rc;
> +     int nid, rc = 0;
>       u64 hotplug_start_paddr;
>       unsigned long balloon_hotplug = credit;
> +     unsigned long pfn;
>
>       hotplug_start_paddr = PFN_PHYS(SECTION_ALIGN_UP(max_pfn));
>       balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
>       nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>
> -     rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << 
> PAGE_SHIFT);
> +     for (pfn = PFN_DOWN(hotplug_start_paddr);
> +          !rc && pfn < PFN_DOWN(hotplug_start_paddr) + balloon_hotplug;
> +          pfn++)
> +             if (!set_phys_to_machine(pfn, INVALID_P2M_ENTRY))

rc = set_phys_to_machine(pfn, INVALID_P2M_ENTRY)?

> +                     rc = 1;

I do not think that this stuff is needed for HVM or PVH guests.

> +     if (!rc)
> +             rc = add_memory(nid, hotplug_start_paddr,
> +                             balloon_hotplug << PAGE_SHIFT);
>
>       if (rc) {
>               pr_warn("Cannot add additional memory (%i)\n", rc);

It will be nice to know what part of infrastructure failed.
Could you create separate pr_warn() message for set_phys_to_machine()?

Daniel

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