linux-kernel - Re: [Xen-devel] [PATCH 08/11] xen p2m: transparently change the p2m mappings in the m2p override

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Date:	Wed, 15 Dec 2010 15:36:34 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	stefano.stabellini@...citrix.com
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH 08/11] xen p2m: transparently change the p2m
 mappings in the m2p override

On 12/15/2010 05:40 AM, stefano.stabellini@...citrix.com wrote:
> From: Stefano Stabellini <stefano.stabellini@...citrix.com>
>
> In m2p_add_override store the original mfn into page->index and then
> change the p2m mapping, setting mfns as FOREIGN_FRAME.
>
> In m2p_remove_override restore the original mapping.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  arch/x86/xen/p2m.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 8db19d5..7dde8e4 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -407,8 +407,11 @@ static unsigned long mfn_hash(unsigned long mfn)
>  void m2p_add_override(unsigned long mfn, struct page *page)
>  {
>  	unsigned long flags;
> +	unsigned long pfn = page_to_pfn(page);
>  	page->private = mfn;
> +	page->index = pfn_to_mfn(pfn);

Is there any risk that a page being used for a granted mfn will end up
getting xen_create_contiguous_region() applied to it via the DMA API? 
That would be messy...

    J


>  
> +	__set_phys_to_machine(pfn, FOREIGN_FRAME(mfn));
>  	spin_lock_irqsave(&m2p_override_lock, flags);
>  	list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
>  	spin_unlock_irqrestore(&m2p_override_lock, flags);
> @@ -420,6 +423,7 @@ void m2p_remove_override(struct page *page)
>  	spin_lock_irqsave(&m2p_override_lock, flags);
>  	list_del(&page->lru);
>  	spin_unlock_irqrestore(&m2p_override_lock, flags);
> +	__set_phys_to_machine(page_to_pfn(page), page->index);
>  }
>  
>  struct page *m2p_find_override(unsigned long mfn)

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