Re: [Xen-devel] Re: [PATCH][RFC] gfx_passthru: warning when vgabios rom has invalid checksum

[Weidong Han <weidong.han@xxxxxxxxx>]

Noboru Iwamatsu wrote:
> Hi Weidong,
>
>  > How did you recalculate it? is it possible to recalculate it when detect
>  > invalid checksum?
>
> Checking and recalculating the VGABIOS checksum is being processed
> in setup_vga_pt() in hw/pass-through.c.
> I thought you have written that part.
>
> If the checksum is invalid, current setup_vga_pt() always overwrites
> it with the recalculated value.
>
> What I mention is: the VGABIOS checksum must have been already
> recalculated by system BIOS. So, when setup_vga_pt() detects the
> invalid one, something might be wrong.
>
> But, I'm not sure all BIOS should work as described in PCIFW Spec.
> Actually, my Q35 had invalid checksum.
>   
Now I understand. Because your Q35 works with recalculated checksum, I 
prefer to only add a warning message, and continue to load rom for gfx 
passthru.
Regards,
Weidong
> I attach another patch:
> This stops loading vgabios if the checksum is wrong.
>
> Signed-off-by: Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>
>
>   
> > Noboru Iwamatsu wrote:
> >     
> > > Hi,
> > >
> > >       
> > > > > Intel DX58SO + GeForce GTS250: checksum is OK.
> > > > > Intel DX58SO + GeForce 9600GT: checksum is OK.
> > > > > Fujitsu Q35 M/B + IGD: checksum is bad.
> > > > >
> > > > >           
> > > > What does "checksum is bad" mean here?
> > > >         
> > > It means shadowed VGABIOS has invalid checksum
> > > and requires recalculating.
> > >
> > >       
> > > > > What do you think, Weidong?
> > > > > Is just warning enough? Or, should we stop loading the rom?
> > > > >
> > > > >
> > > > >           
> > > > Does it still work or not when checksum is bad? If it works, we should
> > > > not stop loading the rom.
> > > >         
> > > When the checksum is bad,
> > > if it is not recalculated, guest has some trouble about handling the
> > > VGA (unable to show BIOS screen, unable to load the gfx driver
> > > properly, ...).
> > >       
> > For this case, it's reasonable to warning and stop loading rom. We
> > didn't encounter this issue.
> >     
> > > If it is recalculated, it seems to work fine.
> > >       
> > How did you recalculate it? is it possible to recalculate it when detect
> > invalid checksum?
> >
> > Regards,
> > Weidong
> >
> >     
> > > Regards,
> > > Noboru.
> > >
> > >       
> > > > Noboru Iwamatsu wrote:
> > > >         
> > > > > Hi,
> > > > >
> > > > > According to the "PCI Firmware Spec Rev 3.0",
> > > > > the system firmware have to write the new checksum after resizing
> > > > > the expansion ROM area.
> > > > >
> > > > > So, when re-using the shadowed VGABIOS, the checksum must
> > > > > be valid, and if it is invalid, we should consider the BIOS has
> > > > > a bug or memory area is corrupted.
> > > > >
> > > > > This patch just add the warning message when checksum requires
> > > > > recalculation.
> > > > >
> > > > > I tried this following environments.
> > > > >
> > > > > Intel DX58SO + GeForce GTS250: checksum is OK.
> > > > > Intel DX58SO + GeForce 9600GT: checksum is OK.
> > > > > Fujitsu Q35 M/B + IGD: checksum is bad.
> > > > >
> > > > >           
> > > > What does "checksum is bad" mean here?
> > > >         
> > > > > What do you think, Weidong?
> > > > > Is just warning enough? Or, should we stop loading the rom?
> > > > >
> > > > >
> > > > >           
> > > > Does it still work or not when checksum is bad? If it works, we should
> > > > not stop loading the rom.
> > > >
> > > > Regards,
> > > > Weidong
> > > >         
> > > > > Regards,
> > > > > Noboru.
> > > > >
> > > > >           
> > >       
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >     
>   

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