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

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Date:	Fri, 20 Mar 2015 14:46:42 +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, pebolle@...cali.nl
Subject: Re: [Patch V2 2/2] xen: before ballooning hotplugged memory, set
 frames to invalid

On Fri, Mar 20, 2015 at 01:55:39PM +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>

In general...

Reviewed-by: Daniel Kiper <daniel.kiper@...cle.com>

... but...

> ---
>  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;
> +			}
> +	}
> +#endif

Should not we fill everything above "maxmem" with
INVALID_P2M_ENTRY at boot time?

Daniel
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