Messages in this thread Patch in this message | | | Date | Fri, 2 Oct 2015 15:09:08 +0100 | From | David Vrabel <> | Subject | Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux |
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On 30/09/15 11:45, Julien Grall wrote: > For ARM64 guests, Linux is able to support either 64K or 4K page > granularity. Although, the hypercall interface is always based on 4K > page granularity. > > With 64K page granularity, a single page will be spread over multiple > Xen frame. > > To avoid splitting the page into 4K frame, take advantage of the > extent_order field to directly allocate/free chunk of the Linux page > size. > > Note that PVMMU is only used for PV guest (which is x86) and the page > granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure > that because the code has not been modified.
This causes a BUG() in x86 PV guests when decreasing the reservation.
Xen says:
(XEN) d0v2 Error pfn 0: rd=0 od=32753 caf=8000000000000001 taf=7400000000000001 (XEN) memory.c:250:d0v2 Bad page free for domain 0
And Linux BUGs with:
[ 82.032654] kernel BUG at /anfs/drall/scratch/davidvr/x86/linux/drivers/xen/balloon.c:540!
Which is a non-zero return value from the decrease_reservation hypercall.
The frame_list[] has been incorrectly populated. The below patch fixes it for me. Please test as well.
--- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -504,9 +504,10 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) * Setup the frame, update direct mapping, invalidate P2M, * and add to balloon. */ + i = 0; list_for_each_entry_safe(page, tmp, &pages, lru) { /* XENMEM_decrease_reservation requires a GFN */ - frame_list[i] = xen_page_to_gfn(page); + frame_list[i++] = xen_page_to_gfn(page);
#ifdef CONFIG_XEN_HAVE_PVMMU /* David
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