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

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Date:	Tue, 8 May 2012 14:24:19 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"JBeulich@...e.com" <JBeulich@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] auto balloon initial domain and fix
 dom0_mem=X inconsistencies (v5).

On Tue, May 08, 2012 at 07:12:18PM +0100, David Vrabel wrote:
> 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.

Yeah. Just have this in your guest config:

e820_hole=1
pci=["01:00.0"]

(And do the PCI bind/unbind to the xen-pciback module)

but looking at the source there is this comment:
/* Weed out anything under 1MB */

so I think we are fine.

> 
> 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
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
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