Re: [RFC] - Mapping ACPI tables as CACHED

[H. Peter Anvin]

On 07/23/2010 07:26 AM, ykzhao wrote:
> Yes. We can't map the corresponding ACPI region as cached under the
> following case:
>      >No E820_ACPI region is reported by BIOS. In such case the ACPI
> table resides in the NVS region

Why could we not map the NVS region as cached?  That doesn't seem to 
make sense.  In practice, at least, on all BIOSes I've seen the NVS 
region is just another hunk of RAM.

Sample from a real system:

 BIOS-e820: 000000007d6b0000 - 000000007d6cc000 (ACPI data)
 BIOS-e820: 000000007d6cc000 - 000000007d700000 (ACPI NVS)

Both are clearly RAM.

If you're not talking about the e820 NVS region, that might be a 
different thing, but for the ROM region in the legacy area, the fixed 
MTRRs are often set up to allow caching, and we should be able to map 
them cacheable, e.g. on this system:

  00000-9FFFF write-back
  A0000-BFFFF uncachable
  C0000-CFFFF write-protect
  D0000-DFFFF uncachable
  E0000-FFFFF write-protect

Clearly cacheable.

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/