ACPI: use ioremap() in acpi_os_map_memory()

This drops the post-boot use of __acpi_map_table() here again (together
with the somewhat awkward locking), in favor of using ioremap().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/acpi/osl.c
+++ b/xen/drivers/acpi/osl.c
@@ -38,6 +38,7 @@
 #include <xen/spinlock.h>
 #include <xen/domain_page.h>
 #include <xen/efi.h>
+#include <xen/vmap.h>
 
 #define _COMPONENT		ACPI_OS_SERVICES
 ACPI_MODULE_NAME("osl")
@@ -83,20 +84,25 @@ acpi_physical_address __init acpi_os_get
 	}
 }
 
-static DEFINE_SPINLOCK(map_lock);
-
 void __iomem *
 acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 {
-	if (system_state >= SYS_STATE_active)
-		spin_lock(&map_lock);
+	if (system_state >= SYS_STATE_active) {
+		unsigned long pfn = PFN_DOWN(phys);
+		unsigned int offs = phys & (PAGE_SIZE - 1);
+
+		/* The low first Mb is always mapped. */
+		if ( !((phys + size - 1) >> 20) )
+			return __va(phys);
+		return __vmap(&pfn, PFN_UP(offs + size), 1, 1, PAGE_HYPERVISOR_NOCACHE) + offs;
+	}
 	return __acpi_map_table(phys, size);
 }
 
 void acpi_os_unmap_memory(void __iomem * virt, acpi_size size)
 {
 	if (system_state >= SYS_STATE_active)
-		spin_unlock(&map_lock);
+		vunmap((void *)((unsigned long)virt & PAGE_MASK));
 }
 
 acpi_status acpi_os_read_port(acpi_io_address port, u32 * value, u32 width)