x86, efivars: firmware bug workarounds should be in platform code

[pandora-kernel.git] / arch / x86 / platform / efi / efi.c

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 1de542b..b20bb92 100644 (file)
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -815,3 +815,28 @@ u64 efi_mem_attributes(unsigned long phys_addr)
        }
        return 0;
 }
+
+/*
+ * Some firmware has serious problems when using more than 50% of the EFI
+ * variable store, i.e. it triggers bugs that can brick machines. Ensure that
+ * we never use more than this safe limit.
+ *
+ * Return EFI_SUCCESS if it is safe to write 'size' bytes to the variable
+ * store.
+ */
+efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
+{
+       efi_status_t status;
+       u64 storage_size, remaining_size, max_size;
+
+       status = efi.query_variable_info(attributes, &storage_size,
+                                        &remaining_size, &max_size);
+       if (status != EFI_SUCCESS)
+               return status;
+
+       if (!storage_size || size > remaining_size || size > max_size ||
+           (remaining_size - size) < (storage_size / 2))
+               return EFI_OUT_OF_RESOURCES;
+
+       return EFI_SUCCESS;
+}