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

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Message-ID: <4D121D57.8010608@goop.org>
Date:	Wed, 22 Dec 2010 07:46:31 -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 12/22/2010 06:53 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Dec 21, 2010 at 02:19:40PM -0800, Jeremy Fitzhardinge wrote:
>> 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.
> Are you OK with me moving then this check:
>
>     if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
>                 BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
>                 return true;
>         }    
> from set_phys_to_machine to __set_phys_to_machine?

Yep - not that we'll see that taken on any current or near-future Xen, I
suspect.

    J
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