Re: [Patch V2 2/2] xen: before ballooning hotplugged memory, set frames to invalid

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 03/20/2015 08:55 AM, 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@citrix.com>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>   drivers/xen/balloon.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 0b52d92..65fedb8 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -229,6 +229,19 @@ static enum bp_state reserve_additional_memory(long credit)
>   	balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
>   	nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>   
> +#ifdef CONFIG_XEN_HAVE_PVMMU
> +	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> +		unsigned long pfn, i;
> +
> +		pfn = PFN_DOWN(hotplug_start_paddr);
> +		for (i = 0; i < balloon_hotplug; i++)
> +			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
> +				pr_warn("set_phys_to_machine() failed, no memory added\n");
> +				return BP_ECANCELED;

I should have asked last time --- should we restore [0..i-1] mapping 
back to identity on error here? I wonder whether leaving those frames as 
invalid (when they are expected to be 'identity') could cause problems 
in the future.

-boris

> +			}
> +	}
> +#endif
> +
>   	rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
>   
>   	if (rc) {