linux-kernel - Re: [PATCH 07/10] xen/mmu: Work with 1-1 mappings when allocating new top/middle entries.

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Date:	Tue, 21 Dec 2010 14:37:46 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, hpa@...or.com,
	Jan Beulich <JBeulich@...ell.com>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad@...nel.org>
Subject: Re: [PATCH 07/10] xen/mmu: Work with 1-1 mappings when allocating
 new top/middle entries.

On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> We were not properly taking under advisement the 1-1 mappings
> when a large area of memory was ballooned out.

Could you expand on this?  What does it mean?

    J

> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/mmu.c |   13 ++++++++-----
>  1 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index bd02e7d..92f4fec 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -464,7 +464,7 @@ static void free_p2m_page(void *p)
>  static bool alloc_p2m(unsigned long pfn)
>  {
>  	unsigned topidx, mididx;
> -	unsigned long ***top_p, **mid;
> +	unsigned long ***top_p, **mid, **mid_orig;
>  	unsigned long *top_mfn_p, *mid_mfn;
>  
>  	topidx = p2m_top_index(pfn);
> @@ -473,15 +473,16 @@ static bool alloc_p2m(unsigned long pfn)
>  	top_p = &p2m_top[topidx];
>  	mid = *top_p;
>  
> -	if (mid == p2m_mid_identity) {
> +	if (mid == p2m_mid_identity || mid == p2m_mid_missing) {
>  		/* Mid level is missing, allocate a new one */
> +		mid_orig = mid;
>  		mid = alloc_p2m_page();
>  		if (!mid)
>  			return false;
>  
>  		p2m_mid_init(mid, p2m_identity);
>  
> -		if (cmpxchg(top_p, p2m_mid_identity, mid) != p2m_mid_identity)
> +		if (cmpxchg(top_p, mid_orig, mid) != mid_orig)
>  			free_p2m_page(mid);
>  	}
>  
> @@ -510,9 +511,11 @@ static bool alloc_p2m(unsigned long pfn)
>  			p2m_top_mfn_p[topidx] = mid_mfn;
>  	}
>  
> -	if (p2m_top[topidx][mididx] == p2m_identity) {
> +	if (p2m_top[topidx][mididx] == p2m_identity ||
> +	    p2m_top[topidx][mididx] == p2m_missing) {
>  		/* p2m leaf page is missing */
>  		unsigned long *p2m;
> +		unsigned long *p2m_orig = p2m_top[topidx][mididx];
>  
>  		p2m = alloc_p2m_page();
>  		if (!p2m)
> @@ -520,7 +523,7 @@ static bool alloc_p2m(unsigned long pfn)
>  
>  		p2m_init(p2m);
>  
> -		if (cmpxchg(&mid[mididx], p2m_identity, p2m) != p2m_identity)
> +		if (cmpxchg(&mid[mididx], p2m_orig, p2m) != p2m_orig)
>  			free_p2m_page(p2m);
>  		else
>  			mid_mfn[mididx] = virt_to_mfn(p2m);

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