[PATCH 4/9] Revert "x86: Switch QEMU over to use the bochs driver"

[Bin Meng]

Hi Simon,

On Mon, Jul 31, 2023 at 10:37 PM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Bin,
>
> On Mon, 31 Jul 2023 at 08:32, Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > Hi Simon,
> >
> > On Sat, Jul 29, 2023 at 1:32 AM Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Bin,
> > >
> > > On Fri, 28 Jul 2023 at 09:46, Bin Meng <bmeng.cn at gmail.com> wrote:
> > > >
> > > > Hi Simon,
> > > >
> > > > On Mon, Jul 24, 2023 at 10:52 PM Simon Glass <sjg at chromium.org> wrote:
> > > > >
> > > > > Unfortunately the bochs driver does not currently work with distros. It
> > > > > causes a hang sometime between grub menu selection and the OS displaying
> > > > > something.
> > > >
> > > > Does this reproduce reliably?
> > >
> > > Yes, it does.
> > >
> > > BTW I've also hit another problem with '-M accel-kvm' which hangs on
> > > the move to 64-bit mode. Oddly if I boot U-Boot from coreboot, the
> > > problem goes away. So perhaps coreboot is doing some x86 init which
> > > U-Boot is missing.
> >
> > This indicates a kvm-x86 bug. I think you can simplify a test case and
> > report it to the KVM mailing list.
>
> Firstly it doesn't really matter, since it doesn't work, so we do need
> to revert.

Agreed, but before we revert this, I would like to see we investigate
this issue a little bit further.

I enabled the grub debug output today and not sure if grub jumps to
the kernel entry yet:

kern/verifiers.c:214: string: boot, type: 2
loader/efi/linux_sb.c:55: kernel_addr: 0x1000000 handover_offset: 0x190 params:
0x7ce63000

>
> Secondly I am not sure it kvm's fault, since the problem does not
> happen with coreboot. I will see if I can isolate what coreboot is
> doing differently, but not sure that that fix will make the release.

Does the 64-bit mode switch ever work on a real x86 board? If yes,
then it's very likely a KVM bug.

If not, then we can check the coreboot to find out the difference.

Regards,
Bin