linux-kernel - Re: [PATCH 01/10] xen: Make all reserved pages for the balloon be INVALID_P2M

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Date:	Tue, 21 Dec 2010 14:19:40 -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 01/10] xen: Make all reserved pages for the balloon be
 INVALID_P2M_ENTRY.

On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> This patch prepares ourselves for the case where void entries in the P2M
> tree structure do not necessarily imply that the pages are missing.
> With this, we diligently set regions that will be used by the
> balloon driver to be INVALID_P2M_ENTRY and under the ownership
> of the balloon driver.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/xen/setup.c  |    8 ++++++++
>  drivers/xen/balloon.c |    1 +
>  2 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index b5a7f92..d984d36 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -52,6 +52,8 @@ phys_addr_t xen_extra_mem_start, xen_extra_mem_size;
>  
>  static __init void xen_add_extra_mem(unsigned long pages)
>  {
> +	unsigned long pfn;
> +
>  	u64 size = (u64)pages * PAGE_SIZE;
>  	u64 extra_start = xen_extra_mem_start + xen_extra_mem_size;
>  
> @@ -66,6 +68,11 @@ static __init void xen_add_extra_mem(unsigned long pages)
>  	xen_extra_mem_size += size;
>  
>  	xen_max_p2m_pfn = PFN_DOWN(extra_start + size);
> +
> +	for (pfn = PFN_DOWN(extra_start); pfn <= xen_max_p2m_pfn; pfn++) {
> +		BUG_ON(!set_phys_to_machine(pfn, INVALID_P2M_ENTRY));

Use __set_phys_to_machine where you don't expect (or can't allow) any
allocation.

Also, I'm not a fan of hiding real side-effectful code in a BUG_ON
predicate.

> +		BUG_ON(get_phys_to_machine(pfn) != INVALID_P2M_ENTRY);
> +	}
>  }
>  
>  static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
> @@ -105,6 +112,7 @@ static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
>  		     start, end, ret);
>  		if (ret == 1) {
>  			set_phys_to_machine(pfn, INVALID_P2M_ENTRY);

Ditto on this one (I guess I forgot, or it predates the existence of
__set_phys_to_machine).

> +			BUG_ON(get_phys_to_machine(pfn) != INVALID_P2M_ENTRY);
>  			len++;
>  		}
>  	}
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 43f9f02..f82bb48 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -297,6 +297,7 @@ static int decrease_reservation(unsigned long nr_pages)
>  	for (i = 0; i < nr_pages; i++) {
>  		pfn = mfn_to_pfn(frame_list[i]);
>  		set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
> +		BUG_ON(get_phys_to_machine(pfn) != INVALID_P2M_ENTRY);
>  		balloon_append(pfn_to_page(pfn));
>  	}
>  

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