Re: [PATCH 29/29] x86/boot/e820: Treat non-type-2 'reserved' E820 region types as E820_TYPE_RESERVED

[H. Peter Anvin]

On 4/21/25 11:52, Ingo Molnar wrote:
> 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:

... so we should handle 13 accordingly (and probably request that the 
ACPI committee permanently reserve it.  It would have been better to use 
negative numbers for OS-specific things.)

However, if we run into a value that we have never seen, say something 
like 84, we shouldn't assume that it is safe to do anything at all to 
it; in particular we really don't want to assume that it is safe to 
place I/O devices there.

Note that devices may be a priori set up in type 2 memory; it pretty 
much means "this device is treated specially by firmware, don't move it 
around or bad things will happen."

	-hpa