[Xen-devel] [PATCH] xen/balloon: do not modify the p2m for auto_translate guests

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

decrease_reservation doesn't modify the p2m for auto_translate guests,
but increase_reservation does.
Fix that by avoiding any p2m modifications in both increase_reservation
and decrease_reservation for auto_translated guests.

Avoid allocating or using scratch pages for auto_translated guests.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 drivers/xen/balloon.c |   63 ++++++++++++++++++++++++++-----------------------
 1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 55ea73f..4c02e2b 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -350,17 +350,19 @@ static enum bp_state increase_reservation(unsigned long 
nr_pages)
 
                pfn = page_to_pfn(page);
 
-               set_phys_to_machine(pfn, frame_list[i]);
-
 #ifdef CONFIG_XEN_HAVE_PVMMU
-               /* Link back into the page tables if not highmem. */
-               if (xen_pv_domain() && !PageHighMem(page)) {
-                       int ret;
-                       ret = HYPERVISOR_update_va_mapping(
-                               (unsigned long)__va(pfn << PAGE_SHIFT),
-                               mfn_pte(frame_list[i], PAGE_KERNEL),
-                               0);
-                       BUG_ON(ret);
+               if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+                       set_phys_to_machine(pfn, frame_list[i]);
+
+                       /* Link back into the page tables if not highmem. */
+                       if (!PageHighMem(page)) {
+                               int ret;
+                               ret = HYPERVISOR_update_va_mapping(
+                                               (unsigned long)__va(pfn << 
PAGE_SHIFT),
+                                               mfn_pte(frame_list[i], 
PAGE_KERNEL),
+                                               0);
+                               BUG_ON(ret);
+                       }
                }
 #endif
 
@@ -378,7 +380,6 @@ static enum bp_state decrease_reservation(unsigned long 
nr_pages, gfp_t gfp)
        enum bp_state state = BP_DONE;
        unsigned long  pfn, i;
        struct page   *page;
-       struct page   *scratch_page;
        int ret;
        struct xen_memory_reservation reservation = {
                .address_bits = 0,
@@ -411,27 +412,29 @@ static enum bp_state decrease_reservation(unsigned long 
nr_pages, gfp_t gfp)
 
                scrub_page(page);
 
+#ifdef CONFIG_XEN_HAVE_PVMMU
                /*
                 * Ballooned out frames are effectively replaced with
                 * a scratch frame.  Ensure direct mappings and the
                 * p2m are consistent.
                 */
-               scratch_page = get_balloon_scratch_page();
-#ifdef CONFIG_XEN_HAVE_PVMMU
-               if (xen_pv_domain() && !PageHighMem(page)) {
-                       ret = HYPERVISOR_update_va_mapping(
-                               (unsigned long)__va(pfn << PAGE_SHIFT),
-                               pfn_pte(page_to_pfn(scratch_page),
-                                       PAGE_KERNEL_RO), 0);
-                       BUG_ON(ret);
-               }
-#endif
                if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                        unsigned long p;
+                       struct page   *scratch_page = 
get_balloon_scratch_page();
+
+                       if (!PageHighMem(page)) {
+                               ret = HYPERVISOR_update_va_mapping(
+                                               (unsigned long)__va(pfn << 
PAGE_SHIFT),
+                                               
pfn_pte(page_to_pfn(scratch_page),
+                                                       PAGE_KERNEL_RO), 0);
+                               BUG_ON(ret);
+                       }
                        p = page_to_pfn(scratch_page);
                        __set_phys_to_machine(pfn, pfn_to_mfn(p));
+
+                       put_balloon_scratch_page();
                }
-               put_balloon_scratch_page();
+#endif
 
                balloon_append(pfn_to_page(pfn));
        }
@@ -627,15 +630,17 @@ static int __init balloon_init(void)
        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;
+       if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+               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);
        }
-       register_cpu_notifier(&balloon_cpu_notifier);
 
        pr_info("Initialising balloon driver\n");
 
-- 
1.7.10.4


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