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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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[PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-30 12:50 +0200
  [PATCH v5 02/22] arm/xen: Drop pte_mfn and mfn_pte Julien Grall <julien.grall@citrix.com> - 2015-09-30 12:50 +0200
  [PATCH v5 07/22] block/xen-blkfront: Store a page rather a pfn in the grant structure Julien Grall <julien.grall@citrix.com> - 2015-09-30 12:50 +0200
  [PATCH v5 09/22] xen/biomerge: Don't allow biovec's to be merged when Linux is not using 4KB pages Julien Grall <julien.grall@citrix.com> - 2015-09-30 12:50 +0200
  [PATCH v5 20/22] arm/xen: Add support for 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 10/22] xen/xenbus: Use Xen page definition Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 16/22] block/xen-blkback: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 11/22] tty/hvc: xen: Use xen page definition Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 22/22] xen/swiotlb: Add support for 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 19/22] xen/privcmd: Add support for Linux 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 17/22] net/xen-netfront: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 14/22] xen/grant-table: Make it running on 64KB granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
    Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity  is the same for Xen and Linux David Vrabel <david.vrabel@citrix.com> - 2015-10-02 16:10 +0200
      Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity  is the same for Xen and Linux Julien Grall <julien.grall@citrix.com> - 2015-10-02 16:40 +0200
        Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity  is the same for Xen and Linux Julien Grall <julien.grall@citrix.com> - 2015-10-02 17:00 +0200
          Re: [PATCH v5 12/22] xen/balloon: Don't rely on the page granularity  is the same for Xen and Linux Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2015-10-02 17:20 +0200
          Re: [Xen-devel] [PATCH v5 12/22] xen/balloon: Don't rely on the page  granularity is the same for Xen and Linux David Vrabel <david.vrabel@citrix.com> - 2015-10-02 17:20 +0200
  [PATCH v5 15/22] block/xen-blkfront: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 13/22] xen/events: fifo: Make it running on 64KB granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 21/22] xen/swiotlb: Pass addresses rather than frame numbers to xen_arch_need_swiotlb Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  [PATCH v5 18/22] net/xen-netback: Make it running on 64KB page granularity Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:00 +0200
  Re: [PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux Mark Rutland <mark.rutland@arm.com> - 2015-09-30 13:40 +0200
    Re: [PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux Julien Grall <julien.grall@citrix.com> - 2015-09-30 13:50 +0200
      Re: [PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux Mark Rutland <mark.rutland@arm.com> - 2015-09-30 15:10 +0200
  Re: [Xen-devel] [PATCH v5 00/22] xen/arm64: Add support for 64KB  page in Linux David Vrabel <david.vrabel@citrix.com> - 2015-10-01 17:20 +0200

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