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

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Message-ID: <20150319162141.GG27971@olila.local.net-space.pl>
Date:	Thu, 19 Mar 2015 17:21:41 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
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 2/2] xen: before ballooning hotplugged memory, set frames
 to invalid

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@...rix.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  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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