Re: [Xen-devel] [PATCH] auto balloon initial domain and fix dom0_mem=Xinconsistencies (v5).

From: David Vrabel
Date: Tue May 08 2012 - 14:12:18 EST

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@xxxxxxxxxx>
>>> ---
>> [...]
>>> --- 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.

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