2 files changed, 29 insertions, 0 deletions

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index b3dbbdbd2a42..f7f928c315da 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -777,6 +777,34 @@ static void __init runtime_code_page_mkexec(void)
 }
 
 /*
+ * We can't ioremap data in EFI boot services RAM, because we've already mapped
+ * it as RAM.  So, look it up in the existing EFI memory map instead.  Only
+ * callable after efi_enter_virtual_mode and before efi_free_boot_services.
+ */
+void __iomem *efi_lookup_mapped_addr(u64 phys_addr)
+{
+        void *p;
+        if (WARN_ON(!memmap.map))
+                return NULL;
+        for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
+                efi_memory_desc_t *md = p;
+                u64 size = md->num_pages << EFI_PAGE_SHIFT;
+                u64 end = md->phys_addr + size;
+                if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
+                    md->type != EFI_BOOT_SERVICES_CODE &&
+                    md->type != EFI_BOOT_SERVICES_DATA)
+                        continue;
+                if (!md->virt_addr)
+                        continue;
+                if (phys_addr >= md->phys_addr && phys_addr < end) {
+                        phys_addr += md->virt_addr - md->phys_addr;
+                        return (__force void __iomem *)(unsigned long)phys_addr;
+                }
+        }
+        return NULL;
+}
+
+/*
  * This function will switch the EFI runtime services to virtual mode.
  * Essentially, look through the EFI memmap and map every region that
  * has the runtime attribute bit set in its memory descriptor and update
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 5782114f4838..fff135d9375e 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -501,6 +501,7 @@ extern void efi_free_boot_services(void);
 #else
 static inline void efi_free_boot_services(void) {}
 #endif
+extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 extern u64 efi_get_iobase (void);
 extern u32 efi_mem_type (unsigned long phys_addr);
 extern u64 efi_mem_attributes (unsigned long phys_addr);