On Tue, 27 Jan 2026 13:18:50 +0100,
Crystal Kolipe <kolipe.c@exoticsilicon.com> wrote:
> 
> On Tue, Jan 27, 2026 at 11:31:50AM +0000, Stuart Henderson wrote:
> > On 2026/01/27 12:05, Kirill A. Korinsky wrote:
> > > On Tue, 27 Jan 2026 10:21:02 +0100,
> > > Crystal Kolipe <kolipe.c@exoticsilicon.com> wrote:
> > > > Whilst it fixes your machine, how confident can we be that this is harmless on
> > > > others?
> > > > 
> > > > It's perfectly valid to have no graphics hardware at all and run entirely from
> > > > a serial console, so this could plausibly break machines that are currently
> > > > working just fine.
> > > > 
> > > 
> > > Well, here my assumption that on amd64, both the VGA legacy memory region
> > > and I/O ports is still reserved and not used.
> > 
> > if my reading is correct then I think that is ok in this case (but I'm
> > not 100%) ..
> > 
> > boot> machine mem
> > Region 0: type 1 at 0x0 for 639KB
> > Region 1: type 2 at 0x9fc00 for 1KB
> > Region 2: type 2 at 0xf0000 for 64KB
> > Region 3: type 1 at 0x100000 for 2078296KB
> > Region 4: type 2 at 0x7ee96000 for 17832KB
> > Region 5: type 2 at 0xf8000000 for 65536KB
> > Region 6: type 2 at 0xfec10000 for 4KB
> > Region 7: type 2 at 0xfed40000 for 20KB
> > Low ram: 639KB  High ram: 2078296KB
> > Total free memory: 2078935KB
> 
> The VGA memory space is certainly marked as reserved.
> 
> But 'reserved' doesn't mean that writing arbitrary values to those addresses
> is harmless.
> 

But for compatiblity it should stay reserved for VGA, and to reuse it for
something else BIOS should have two code paths: when VGA is avaialbel and
when it isn't.

This is quite small region and introduce two code path seems strange.

But, again, here many assumptions.

-- 
wbr, Kirill