linux-kernel - Re: [Xen-devel] [PATCH] auto balloon initial domain and fix dom0

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Date:	Tue, 8 May 2012 19:12:18 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"JBeulich@...e.com" <JBeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH] auto balloon initial domain and fix dom0_mem=X
 inconsistencies (v5).

On 07/05/12 19:48, Konrad Rzeszutek Wilk wrote:
> On Thu, May 03, 2012 at 05:27:27PM +0100, David Vrabel wrote:
>> On 03/05/12 16:15, David Vrabel wrote:
>>>
>>> xen: update VA mapping when releasing memory during setup
>>>
>>> In xen_memory_setup(), if a page that is being released has a VA
>>> mapping this must also be updated.  Otherwise, the page will be not
>>> released completely -- it will still be referenced in Xen and won't be
>>> freed util the mapping is removed and this prevents it from being
>>> reallocated at a different PFN.
>>>
>>> This was already being done for the ISA memory region in
>>> xen_ident_map_ISA() but on many systems this was omitting a few pages
>>> as many systems marked a few pages below the ISA memory region as
>>> reserved in the e820 map.
>>>
>>> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
>>> ---
>> [...]
>>> --- a/arch/x86/xen/mmu.c
>>> +++ b/arch/x86/xen/mmu.c
>>> @@ -1929,29 +1929,6 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
>>>  #endif
>>>  }
>>>  
>>> -void __init xen_ident_map_ISA(void)
>>> -{
>>> -	unsigned long pa;
>>> -
>>> -	/*
>>> -	 * If we're dom0, then linear map the ISA machine addresses into
>>> -	 * the kernel's address space.
>>> -	 */
>>> -	if (!xen_initial_domain())
>>> -		return;
>>
>> It might look like this test has gone, however the new code which
>> updates the VA mapping uses the e820 map and for a domU its map will not
>> have a ISA region so there's no mapping to be updated.
> 
> What if you use e820_hole=1 and the pci=xx in the guest?

Are these xl configuration options? I'm not familiar with xl.

The PCI memory hole should be above 3 GiB so this hole will be will
above the memory that will be initially mapped at boot.

I've not managed to persuade my test box to passthrough a PCI device to
a guest (using xapi as the toolstack) to confirm, though.  I'll have
another go tomorrow.

David
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