linux-kernel - Re: [Xen-devel] [PATCH v3 12/20] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux

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Date:	Thu, 20 Aug 2015 10:59:57 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	Wei Liu <wei.liu2@...rix.com>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	"David Vrabel" <david.vrabel@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v3 12/20] xen/balloon: Don't rely on the page
 granularity is the same for Xen and Linux

On 07/08/15 17:46, Julien Grall wrote:
> For ARM64 guests, Linux is able to support either 64K or 4K page
> granularity. Although, the hypercall interface is always based on 4K
> page granularity.
> 
> With 64K page granularity, a single page will be spread over multiple
> Xen frame.
> 
> To avoid splitting the page into 4K frame, take advantage of the
> extent_order field to directly allocate/free chunk of the Linux page
> size.
> 
> Note that PVMMU is only used for PV guest (which is x86) and the page
> granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure
> that because the code has not been modified.
[...]
>  #ifdef CONFIG_XEN_HAVE_PVMMU
> +		/* We don't support PV MMU when Linux and Xen is using
> +		 * different page granularity.
> +		 */
> +		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);

You don't need this BUILD_BUG_ON() twice.

Otherwise,

Reviewed-by: David Vrabel <david.vrabel@...rix.com>

David
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