xen/balloon: Mark unallocated host memory as UNUSABLE

Commit f5775e0b6116 ("x86/xen: discard RAM regions above the maximum
reservation") left host memory not assigned to dom0 as available for
memory hotplug.

Unfortunately this also meant that those regions could be used by
others. Specifically, commit fa564ad96366 ("x86/PCI: Enable a 64bit BAR
on AMD Family 15h (Models 00-1f, 30-3f, 60-7f)") may try to map those
addresses as MMIO.

To prevent this mark unallocated host memory as E820_TYPE_UNUSABLE (thus
effectively reverting f5775e0b6116) and keep track of that region as
a hostmem resource that can be used for the hotplug.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

2 files changed, 83 insertions, 4 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d669e9d89001..c9081c6671f0 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1,8 +1,12 @@
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+#include <linux/bootmem.h>
+#endif
 #include <linux/cpu.h>
 #include <linux/kexec.h>
 
 #include <xen/features.h>
 #include <xen/page.h>
+#include <xen/interface/memory.h>
 
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
@@ -331,3 +335,80 @@ void xen_arch_unregister_cpu(int num)
 }
 EXPORT_SYMBOL(xen_arch_unregister_cpu);
 #endif
+
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+void __init arch_xen_balloon_init(struct resource *hostmem_resource)
+{
+	struct xen_memory_map memmap;
+	int rc;
+	unsigned int i, last_guest_ram;
+	phys_addr_t max_addr = PFN_PHYS(max_pfn);
+	struct e820_table *xen_e820_table;
+	const struct e820_entry *entry;
+	struct resource *res;
+
+	if (!xen_initial_domain())
+		return;
+
+	xen_e820_table = kmalloc(sizeof(*xen_e820_table), GFP_KERNEL);
+	if (!xen_e820_table)
+		return;
+
+	memmap.nr_entries = ARRAY_SIZE(xen_e820_table->entries);
+	set_xen_guest_handle(memmap.buffer, xen_e820_table->entries);
+	rc = HYPERVISOR_memory_op(XENMEM_machine_memory_map, &memmap);
+	if (rc) {
+		pr_warn("%s: Can't read host e820 (%d)\n", __func__, rc);
+		goto out;
+	}
+
+	last_guest_ram = 0;
+	for (i = 0; i < memmap.nr_entries; i++) {
+		if (xen_e820_table->entries[i].addr >= max_addr)
+			break;
+		if (xen_e820_table->entries[i].type == E820_TYPE_RAM)
+			last_guest_ram = i;
+	}
+
+	entry = &xen_e820_table->entries[last_guest_ram];
+	if (max_addr >= entry->addr + entry->size)
+		goto out; /* No unallocated host RAM. */
+
+	hostmem_resource->start = max_addr;
+	hostmem_resource->end = entry->addr + entry->size;
+
+	/*
+	 * Mark non-RAM regions between the end of dom0 RAM and end of host RAM
+	 * as unavailable. The rest of that region can be used for hotplug-based
+	 * ballooning.
+	 */
+	for (; i < memmap.nr_entries; i++) {
+		entry = &xen_e820_table->entries[i];
+
+		if (entry->type == E820_TYPE_RAM)
+			continue;
+
+		if (entry->addr >= hostmem_resource->end)
+			break;
+
+		res = kzalloc(sizeof(*res), GFP_KERNEL);
+		if (!res)
+			goto out;
+
+		res->name = "Unavailable host RAM";
+		res->start = entry->addr;
+		res->end = (entry->addr + entry->size < hostmem_resource->end) ?
+			    entry->addr + entry->size : hostmem_resource->end;
+		rc = insert_resource(hostmem_resource, res);
+		if (rc) {
+			pr_warn("%s: Can't insert [%llx - %llx) (%d)\n",
+				__func__, res->start, res->end, rc);
+			kfree(res);
+			goto  out;
+		}
+	}
+
+ out:
+	kfree(xen_e820_table);
+}
+#endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index ac55c02f98e9..e9011e1ee3de 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -807,7 +807,6 @@ char * __init xen_memory_setup(void)
 	addr = xen_e820_table.entries[0].addr;
 	size = xen_e820_table.entries[0].size;
 	while (i < xen_e820_table.nr_entries) {
-		bool discard = false;
 
 		chunk_size = size;
 		type = xen_e820_table.entries[i].type;
@@ -823,11 +822,10 @@ char * __init xen_memory_setup(void)
 				xen_add_extra_mem(pfn_s, n_pfns);
 				xen_max_p2m_pfn = pfn_s + n_pfns;
 			} else
-				discard = true;
+				type = E820_TYPE_UNUSABLE;
 		}
 
-		if (!discard)
-			xen_align_and_add_e820_region(addr, chunk_size, type);
+		xen_align_and_add_e820_region(addr, chunk_size, type);
 
 		addr += chunk_size;
 		size -= chunk_size;