Re: [PATCH] xen/balloon: do not modify the p2m for auto_translate guests

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Dec 11, 2013 at 04:58:42PM +0000, Stefano Stabellini wrote:
> decrease_reservation doesn't modify the p2m for auto_translate guests,
> but increase_reservation does.
> Fix that by avoiding any p2m modifications in both increase_reservation
> and decrease_reservation for auto_translated guests.
> 
> Avoid allocating or using scratch pages for auto_translated guests.

Mukesh, is this similar to your patch?
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  drivers/xen/balloon.c |   63 ++++++++++++++++++++++++++-----------------------
>  1 file changed, 34 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 55ea73f..4c02e2b 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -350,17 +350,19 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
>  
>  		pfn = page_to_pfn(page);
>  
> -		set_phys_to_machine(pfn, frame_list[i]);
> -
>  #ifdef CONFIG_XEN_HAVE_PVMMU
> -		/* Link back into the page tables if not highmem. */
> -		if (xen_pv_domain() && !PageHighMem(page)) {
> -			int ret;
> -			ret = HYPERVISOR_update_va_mapping(
> -				(unsigned long)__va(pfn << PAGE_SHIFT),
> -				mfn_pte(frame_list[i], PAGE_KERNEL),
> -				0);
> -			BUG_ON(ret);
> +		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> +			set_phys_to_machine(pfn, frame_list[i]);
> +
> +			/* Link back into the page tables if not highmem. */
> +			if (!PageHighMem(page)) {
> +				int ret;
> +				ret = HYPERVISOR_update_va_mapping(
> +						(unsigned long)__va(pfn << PAGE_SHIFT),
> +						mfn_pte(frame_list[i], PAGE_KERNEL),
> +						0);
> +				BUG_ON(ret);
> +			}
>  		}
>  #endif
>  
> @@ -378,7 +380,6 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
>  	enum bp_state state = BP_DONE;
>  	unsigned long  pfn, i;
>  	struct page   *page;
> -	struct page   *scratch_page;
>  	int ret;
>  	struct xen_memory_reservation reservation = {
>  		.address_bits = 0,
> @@ -411,27 +412,29 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
>  
>  		scrub_page(page);
>  
> +#ifdef CONFIG_XEN_HAVE_PVMMU
>  		/*
>  		 * Ballooned out frames are effectively replaced with
>  		 * a scratch frame.  Ensure direct mappings and the
>  		 * p2m are consistent.
>  		 */
> -		scratch_page = get_balloon_scratch_page();
> -#ifdef CONFIG_XEN_HAVE_PVMMU
> -		if (xen_pv_domain() && !PageHighMem(page)) {
> -			ret = HYPERVISOR_update_va_mapping(
> -				(unsigned long)__va(pfn << PAGE_SHIFT),
> -				pfn_pte(page_to_pfn(scratch_page),
> -					PAGE_KERNEL_RO), 0);
> -			BUG_ON(ret);
> -		}
> -#endif
>  		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
>  			unsigned long p;
> +			struct page   *scratch_page = get_balloon_scratch_page();
> +
> +			if (!PageHighMem(page)) {
> +				ret = HYPERVISOR_update_va_mapping(
> +						(unsigned long)__va(pfn << PAGE_SHIFT),
> +						pfn_pte(page_to_pfn(scratch_page),
> +							PAGE_KERNEL_RO), 0);
> +				BUG_ON(ret);
> +			}
>  			p = page_to_pfn(scratch_page);
>  			__set_phys_to_machine(pfn, pfn_to_mfn(p));
> +
> +			put_balloon_scratch_page();
>  		}
> -		put_balloon_scratch_page();
> +#endif
>  
>  		balloon_append(pfn_to_page(pfn));
>  	}
> @@ -627,15 +630,17 @@ static int __init balloon_init(void)
>  	if (!xen_domain())
>  		return -ENODEV;
>  
> -	for_each_online_cpu(cpu)
> -	{
> -		per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
> -		if (per_cpu(balloon_scratch_page, cpu) == NULL) {
> -			pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
> -			return -ENOMEM;
> +	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
> +		for_each_online_cpu(cpu)
> +		{
> +			per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
> +			if (per_cpu(balloon_scratch_page, cpu) == NULL) {
> +				pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
> +				return -ENOMEM;
> +			}
>  		}
> +		register_cpu_notifier(&balloon_cpu_notifier);
>  	}
> -	register_cpu_notifier(&balloon_cpu_notifier);
>  
>  	pr_info("Initialising balloon driver\n");
>  
> -- 
> 1.7.10.4
>