linux-kernel - [PATCH 29/29] x86/boot/e820: Treat non-type-2 'reserved' E820 region types as E820_TYPE

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Message-ID: <20250421185210.3372306-30-mingo@kernel.org>
Date: Mon, 21 Apr 2025 20:52:09 +0200
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Andy Shevchenko <andy@...nel.org>,
	Arnd Bergmann <arnd@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 29/29] x86/boot/e820: Treat non-type-2 'reserved' E820 region types as E820_TYPE_RESERVED

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.

Follow the ACPI spec and change the Linux E820 code to treat unknown/reserved
E820 region types as E820_TYPE_RESERVED device memory regions.

Reported-by: Paul Menzel <pmenzel@...gen.mpg.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Andy Shevchenko <andy@...nel.org>
Cc: Arnd Bergmann <arnd@...nel.org>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 arch/x86/kernel/e820.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index f9caf4c922ea..c36261d78109 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1140,8 +1140,10 @@ __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:
-	default:
 		return false;
+	/* Reserved E820 types should be treated as device memory regions: */
+	default:
+		return true;
 	}
 }
 
-- 
2.45.2