acpi, x86: Implement arch_apei_get_mem_attributes()

... to allow an arch specific implementation of getting page
protection type associated with a physical address.

On x86, we currently have no way to look up the EFI memory map
attributes for a region in a consistent way, because the
memmap is discarded after efi_free_boot_services(). So if
you call efi_mem_attributes() during boot and at runtime,
you could theoretically see different attributes.

Since we are yet to see any x86 platforms that require
anything other than PAGE_KERNEL (some arm64 platforms
require the equivalent of PAGE_KERNEL_NOCACHE), return that
until we know differently.

Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@codeaurora.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1438936621-5215-5-git-send-email-matt@codeblueprint.co.uk
[ Small fixes to spelling. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/acpi.h

@@ -32,6 +32,10 @@
 #include <asm/mpspec.h>
 #include <asm/realmode.h>
 
+#ifdef CONFIG_ACPI_APEI
+# include <asm/pgtable_types.h>
+#endif
+
 #ifdef CONFIG_ACPI
 extern int acpi_lapic;
 extern int acpi_ioapic;
@@ -147,4 +151,23 @@ extern int x86_acpi_numa_init(void);
 
 #define acpi_unlazy_tlb(x)	leave_mm(x)
 
+#ifdef CONFIG_ACPI_APEI
+static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
+{
+	/*
+	 * We currently have no way to look up the EFI memory map
+	 * attributes for a region in a consistent way, because the
+	 * memmap is discarded after efi_free_boot_services(). So if
+	 * you call efi_mem_attributes() during boot and at runtime,
+	 * you could theoretically see different attributes.
+	 *
+	 * Since we are yet to see any x86 platforms that require
+	 * anything other than PAGE_KERNEL (some arm64 platforms
+	 * require the equivalent of PAGE_KERNEL_NOCACHE), return that
+	 * until we know differently.
+	 */
+	 return PAGE_KERNEL;
+}
+#endif
+
 #endif /* _ASM_X86_ACPI_H */