xen/balloon: Seperate the auto-translate logic properly (v2)

The auto-xlat logic vs the non-xlat means that we don't need to for
auto-xlat guests (like PVH, HVM or ARM):
 - use P2M
 - use scratch page.

However the code in increase_reservation does modify the p2m for
auto_translate guests, but not in decrease_reservation.

Fix that by avoiding any p2m modifications in both increase_reservation
and decrease_reservation for auto_translated guests.

And also avoid allocating or using scratch pages for auto_translated guests.

Lastly, since !auto-xlat is really another way of saying 'xen_pv'
remove the redundant 'xen_pv_domain' check.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
[v2: Updated the description]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 34 insertions, 29 deletions

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 55ea73f7c70b..4c02e2b94103 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");