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
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