linux-kernel - [PATCH 3.16.y-ckt 116/144] xen/balloon: before adding hotplugged memory, set frames to invalid

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Date:	Tue, 21 Apr 2015 16:31:41 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Juergen Gross <jgross@...e.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 116/144] xen/balloon: before adding hotplugged memory, set frames to invalid

3.16.7-ckt10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Juergen Gross <jgross@...e.com>

commit 3c56b3a12ce52f361468cbdd2f79b2f3b8da0ea6 upstream.

Commit 25b884a83d487fd62c3de7ac1ab5549979188482 ("x86/xen: set
regions above the end of RAM as 1:1") introduced a regression.

To be able to add memory pages which were added via memory hotplug to
a pv domain, the pages must be "invalid" instead of "identity" in the
p2m list before they can be added.

Suggested-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Daniel Kiper <daniel.kiper@...cle.com>
Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/xen/balloon.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 5c660c77f03b..8db7abb6ef5a 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -227,6 +227,29 @@ static enum bp_state reserve_additional_memory(long credit)
 	balloon_hotplug = round_up(balloon_hotplug, PAGES_PER_SECTION);
 	nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
 
+#ifdef CONFIG_XEN_HAVE_PVMMU
+        /*
+         * add_memory() will build page tables for the new memory so
+         * the p2m must contain invalid entries so the correct
+         * non-present PTEs will be written.
+         *
+         * If a failure occurs, the original (identity) p2m entries
+         * are not restored since this region is now known not to
+         * conflict with any devices.
+         */ 
+	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+		unsigned long pfn, i;
+
+		pfn = PFN_DOWN(hotplug_start_paddr);
+		for (i = 0; i < balloon_hotplug; i++) {
+			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
+				pr_warn("set_phys_to_machine() failed, no memory added\n");
+				return BP_ECANCELED;
+			}
+                }
+	}
+#endif
+
 	rc = add_memory(nid, hotplug_start_paddr, balloon_hotplug << PAGE_SHIFT);
 
 	if (rc) {
--
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