Paul Menzel pointed out that ACPI specification 6.3 defines 'reserved'
E820 region types as E820_TYPE_RESERVED (type 2):

 > Table 15-374 *Address Range Types* in the ACPI specification 6.3 says:
 >
 > > Reserved for future use. OSPM must treat any range of this type as if
 > > the type returned was AddressRangeReserved.

This has relevance for device address regions, which on some firmware such
as CoreBoot, get passed to Linux as type-13 - which the kernel
treats as system regions and registers them as unavailable to drivers:

	static bool __init e820_device_region(enum e820_type type, struct resource *res)

	...

        case E820_TYPE_ACPI:
        case E820_TYPE_NVS:
        case E820_TYPE_UNUSABLE:
        default:
                return false;

Users of such systems will see device breakage on Linux, which they
have to work around with iomem=relaxed kind of boot time hacks to
turn off resource conflict checking.

Partially follow the ACPI spec and add a limited quirk for the
E820_TYPE_13 type, and allow it to be claimed by device drivers
(similarly to E820_TYPE_RESERVED).

Don't change behavior for other unknown types.

Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 arch/x86/include/asm/e820/types.h |  4 ++++
 arch/x86/kernel/e820.c            | 11 +++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/e820/types.h b/arch/x86/include/asm/e820/types.h
index df12f7ee75d3..2430120c2528 100644
--- a/arch/x86/include/asm/e820/types.h
+++ b/arch/x86/include/asm/e820/types.h
@@ -27,6 +27,10 @@ enum e820_type {
 	 *   6 was assigned differently. Some time they will learn... )
 	 */
 	E820_TYPE_PRAM		= 12,
+	/*
+	 * Certain firmware such as CoreBoot uses this type:
+	 */
+	E820_TYPE_13		= 13,
 
 	/*
 	 * Special-purpose memory is indicated to the system via the
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 5260ce6ad466..6c9c00ce8db9 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1075,7 +1075,7 @@ __init static const char * e820_type_to_string(struct e820_entry *entry)
 	case E820_TYPE_PRAM:		return "Persistent Memory (legacy)";
 	case E820_TYPE_PMEM:		return "Persistent Memory";
 	case E820_TYPE_RESERVED:	return "Reserved";
-	case E820_TYPE_SOFT_RESERVED:	return "Soft Reserved";
+	case E820_TYPE_13:		return "Type 13";
 	default:			return "Unknown E820 type";
 	}
 }
@@ -1090,6 +1090,7 @@ __init static unsigned long e820_type_to_iomem_type(struct e820_entry *entry)
 	case E820_TYPE_PRAM:		/* Fall-through: */
 	case E820_TYPE_PMEM:		/* Fall-through: */
 	case E820_TYPE_RESERVED:	/* Fall-through: */
+	case E820_TYPE_13:		/* Fall-through: */
 	case E820_TYPE_SOFT_RESERVED:	/* Fall-through: */
 	default:			return IORESOURCE_MEM;
 	}
@@ -1102,7 +1103,8 @@ __init static unsigned long e820_type_to_iores_desc(struct e820_entry *entry)
 	case E820_TYPE_NVS:		return IORES_DESC_ACPI_NV_STORAGE;
 	case E820_TYPE_PMEM:		return IORES_DESC_PERSISTENT_MEMORY;
 	case E820_TYPE_PRAM:		return IORES_DESC_PERSISTENT_MEMORY_LEGACY;
-	case E820_TYPE_RESERVED:	return IORES_DESC_RESERVED;
+	case E820_TYPE_RESERVED:	/* Fall-through: */
+	case E820_TYPE_13:		return IORES_DESC_RESERVED;
 	case E820_TYPE_SOFT_RESERVED:	return IORES_DESC_SOFT_RESERVED;
 	case E820_TYPE_RAM:		/* Fall-through: */
 	case E820_TYPE_UNUSABLE:	/* Fall-through: */
@@ -1132,6 +1134,7 @@ __init static bool e820_device_region(enum e820_type type, struct resource *res)
 	 */
 	switch (type) {
 	case E820_TYPE_RESERVED:
+	case E820_TYPE_13:
 	case E820_TYPE_SOFT_RESERVED:
 	case E820_TYPE_PRAM:
 	case E820_TYPE_PMEM:
@@ -1140,6 +1143,10 @@ __init static bool e820_device_region(enum e820_type type, struct resource *res)
 	case E820_TYPE_ACPI:
 	case E820_TYPE_NVS:
 	case E820_TYPE_UNUSABLE:
+	/*
+	 * Unknown E820 types should be treated passively, here we
+	 * don't allow them to be claimed by device drivers:
+	 */
 	default:
 		return false;
 	}
-- 
2.45.2