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Date: Tue, 23 Jul 2013 18:27:45 +0100
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: <xen-devel@...ts.xensource.com>
CC: <konrad.wilk@...cle.com>, <stefano.stabellini@...citrix.com>,
<alex@...x.org.uk>, <dcrisan@...xiant.com>,
<ian.campbell@...rix.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 1/2] xen/balloon: set a mapping for ballooned out pages
Currently ballooned out pages are mapped to 0 and have INVALID_P2M_ENTRY
in the p2m. These ballooned out pages are used to map foreign grants
by gntdev and blkback (see alloc_xenballooned_pages).
Allocate a page per cpu and map all the ballooned out pages to the
corresponding mfn. Set the p2m accordingly. This way reading from a
ballooned out page won't cause a kernel crash (see
http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html).
Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
CC: alex@...x.org.uk
CC: dcrisan@...xiant.com
---
drivers/xen/balloon.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++--
include/xen/balloon.h | 3 ++
2 files changed, 58 insertions(+), 3 deletions(-)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 930fb68..b9260dd 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -36,6 +36,7 @@
* IN THE SOFTWARE.
*/
+#include <linux/cpu.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/errno.h>
@@ -50,6 +51,7 @@
#include <linux/notifier.h>
#include <linux/memory.h>
#include <linux/memory_hotplug.h>
+#include <linux/percpu-defs.h>
#include <asm/page.h>
#include <asm/pgalloc.h>
@@ -88,6 +90,8 @@ EXPORT_SYMBOL_GPL(balloon_stats);
/* We increase/decrease in batches which fit in a page */
static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];
+static DEFINE_PER_CPU(struct page *, balloon_scratch_page);
+
#ifdef CONFIG_HIGHMEM
#define inc_totalhigh_pages() (totalhigh_pages++)
@@ -423,7 +427,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
if (xen_pv_domain() && !PageHighMem(page)) {
ret = HYPERVISOR_update_va_mapping(
(unsigned long)__va(pfn << PAGE_SHIFT),
- __pte_ma(0), 0);
+ pfn_pte(page_to_pfn(__get_cpu_var(balloon_scratch_page)),
+ PAGE_KERNEL_RO), 0);
BUG_ON(ret);
}
#endif
@@ -436,7 +441,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
/* No more mappings: invalidate P2M and add to balloon. */
for (i = 0; i < nr_pages; i++) {
pfn = mfn_to_pfn(frame_list[i]);
- __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+ __set_phys_to_machine(pfn,
+ pfn_to_mfn(page_to_pfn(__get_cpu_var(balloon_scratch_page))));
balloon_append(pfn_to_page(pfn));
}
@@ -491,6 +497,18 @@ static void balloon_process(struct work_struct *work)
mutex_unlock(&balloon_mutex);
}
+struct page* get_balloon_scratch_page(void)
+{
+ struct page *ret = get_cpu_var(balloon_scratch_page);
+ BUG_ON(ret == NULL);
+ return ret;
+}
+
+void put_balloon_scratch_page(void)
+{
+ put_cpu_var(balloon_scratch_page);
+}
+
/* Resets the Xen limit, sets new target, and kicks off processing. */
void balloon_set_new_target(unsigned long target)
{
@@ -584,13 +602,47 @@ static void __init balloon_add_region(unsigned long start_pfn,
}
}
+static int __cpuinit balloon_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ int cpu = (long)hcpu;
+ switch (action) {
+ case CPU_UP_PREPARE:
+ if (per_cpu(balloon_scratch_page, cpu) != NULL)
+ break;
+ per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
+ if (per_cpu(balloon_scratch_page, cpu) == NULL) {
+ pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
+ return NOTIFY_BAD;
+ }
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block balloon_cpu_notifier __cpuinitdata = {
+ .notifier_call = balloon_cpu_notify,
+};
+
static int __init balloon_init(void)
{
- int i;
+ int i, cpu;
if (!xen_domain())
return -ENODEV;
+ for_each_online_cpu(cpu)
+ {
+ per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL);
+ if (per_cpu(balloon_scratch_page, cpu) == NULL) {
+ pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu);
+ return -ENOMEM;
+ }
+ }
+ register_cpu_notifier(&balloon_cpu_notifier);
+
pr_info("xen/balloon: Initialising balloon driver.\n");
balloon_stats.current_pages = xen_pv_domain()
diff --git a/include/xen/balloon.h b/include/xen/balloon.h
index cc2e1a7..7a819b7 100644
--- a/include/xen/balloon.h
+++ b/include/xen/balloon.h
@@ -29,6 +29,9 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages,
bool highmem);
void free_xenballooned_pages(int nr_pages, struct page **pages);
+struct page* get_balloon_scratch_page(void);
+void put_balloon_scratch_page(void);
+
struct device;
#ifdef CONFIG_XEN_SELFBALLOONING
extern int register_xen_selfballooning(struct device *dev);
--
1.7.2.5
--
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