x86: introduce clear_fixmap()

... making more obvious what its so far open coded users intend.

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

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -310,7 +310,7 @@ void free_vcpu_guest_context(struct vcpu
     {
         if ( !per_cpu(vgc_pages[i], cpu) )
             continue;
-        __set_fixmap(idx - i, 0, 0);
+        clear_fixmap(idx - i);
         free_domheap_page(per_cpu(vgc_pages[i], cpu));
         per_cpu(vgc_pages[i], cpu) = NULL;
     }
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -2552,7 +2552,7 @@ void __init init_ioapic_mappings(void)
 
         if ( bad_ioapic_register(i) )
         {
-            __set_fixmap(idx, 0, 0);
+            clear_fixmap(idx);
             continue;
         }
 
--- a/xen/arch/x86/mpparse.c
+++ b/xen/arch/x86/mpparse.c
@@ -541,7 +541,7 @@ static inline void __init construct_defa
 static __init void efi_unmap_mpf(void)
 {
 	if (efi_enabled)
-		__set_fixmap(FIX_EFI_MPF, 0, 0);
+		clear_fixmap(FIX_EFI_MPF);
 }
 
 static struct intel_mp_floating *__initdata mpf_found;
--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -112,7 +112,7 @@ static void msix_put_fixmap(struct arch_
 
     if ( --msix->table_refcnt[i] == 0 )
     {
-        __set_fixmap(idx, 0, 0);
+        clear_fixmap(idx);
         msix_fixmap_free(idx);
         msix->table_idx[i] = 0;
     }
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -138,7 +138,7 @@ void __init tboot_probe(void)
                       TXT_PUB_CONFIG_REGS_BASE + TXTCR_SINIT_BASE);
     tboot_copy_memory((unsigned char *)&sinit_size, sizeof(sinit_size),
                       TXT_PUB_CONFIG_REGS_BASE + TXTCR_SINIT_SIZE);
-    __set_fixmap(FIX_TBOOT_MAP_ADDRESS, 0, 0);
+    clear_fixmap(FIX_TBOOT_MAP_ADDRESS);
 }
 
 /* definitions from xen/drivers/passthrough/vtd/iommu.h
@@ -477,7 +477,7 @@ int __init tboot_parse_dmar_table(acpi_t
     dmar_table_raw = xmalloc_array(unsigned char, dmar_table_length);
     tboot_copy_memory(dmar_table_raw, dmar_table_length, pa);
     dmar_table = (struct acpi_table_header *)dmar_table_raw;
-    __set_fixmap(FIX_TBOOT_MAP_ADDRESS, 0, 0);
+    clear_fixmap(FIX_TBOOT_MAP_ADDRESS);
 
     rc = dmar_handler(dmar_table);
     xfree(dmar_table_raw);
--- a/xen/include/asm-x86/fixmap.h
+++ b/xen/include/asm-x86/fixmap.h
@@ -78,6 +78,8 @@ extern void __set_fixmap(
 #define set_fixmap_nocache(idx, phys) \
     __set_fixmap(idx, (phys)>>PAGE_SHIFT, PAGE_HYPERVISOR_NOCACHE)
 
+#define clear_fixmap(idx) __set_fixmap(idx, 0, 0)
+
 #define __fix_to_virt(x) (FIXADDR_TOP - ((x) << PAGE_SHIFT))
 #define __virt_to_fix(x) ((FIXADDR_TOP - ((x)&PAGE_MASK)) >> PAGE_SHIFT)