Re: [PATCH] tools/libs/light: set video_mem for PVH guests

[Andrew Cooper <amc96@xxxxxxxx>]

On 03/12/2021 07:30, Juergen Gross wrote:
> The size of the video memory of PVH guests should be set to 0 in case
> no value has been specified.
>
> Doing not so will leave it to be -1, resulting in an additional 1 kB
> of RAM being advertised in the memory map (here the output of a PVH
> Mini-OS boot with 16 MB of RAM assigned):
>
> Memory map:
> 000000000000-0000010003ff: RAM
> 0000feff8000-0000feffffff: Reserved
> 0000fc008000-0000fc00803f: ACPI
> 0000fc000000-0000fc000fff: ACPI
> 0000fc001000-0000fc007fff: ACPI

The patch itself is fine, but some further observations based on the
memory map alone.

It is rude to provide an unsorted memory map.

The LAPIC range is required to be reserved by the ACPI spec, missing
here.  Conversely, it's unclear what the reserved region is trying to
describe.

Of the 3 ACPI ranges, one is RSDP (the first 64 bytes), one is the info
block (4k), and one is the ACPI tables themselves.

RSDP really ought to be merged into the same block as the rest of the
ACPI tables.

The info block must not be marked ACPI reclaimable RAM, because it is
referenced by AML inside the DSDT/etc.  This is a very serious issue if
the OS actually exercises its right to reclaim those regions and use
them as RAM.

~Andrew