Re: [Xen-devel] [PATCH v4 5/8] hvmloader: Correct bug in low mmio region accounting

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 21/06/13 14:32, Ian Jackson wrote:
> Jan Beulich writes ("Re: [Xen-devel] [PATCH v4 5/8] hvmloader: Correct bug in low 
> mmio region accounting"):
> > On 21.06.13 at 13:19, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> > > But for the first device I think it may be possible for resource->base
> > > not to be a multiple of the bar_sz, and in that case it might be that
> > > the precalculation thinks it will fit when the actual placement
> > > calculation doesn't.
> > >
> > > Do you think this is possible ?
> > This is possible only from an abstract perspective, not in reality:
> > PCI_MEM_START being 0x{f,e,c,8}0000000, PCI_MEM_END being
> > 0xfc000000, and allocations starting with the biggest BARs
> > (where you already correctly noted that BARs are always a power
> > of 2 in size), the current base address can be misaligned only
> > when the BAR size is too large to fit anyway. In which case it'll
> > go into the space above 4Gb, and to that range the precalculation
> > doesn't apply.
> Ah.  Right.  Err, OK.  I'm convinced by this argument.
>
> It's not a good reflection on the clarity of this code, though.
> Perhaps, George, you could mention this issue in a comment or the
> commit message.
Yes, I think I shall.  It is, as Jan says, correct at the present 
moment, but it's not even clear whether that was by accident or by 
design; even if it was by design, there's no guarantee it will remain so 
in the future without at least a comment.
We may want to try to clean this up long-term, but I would really like 
to investigate just punting this whole thing off to SeaBIOS, which is 
being tested and maintained by the KVM folks.
> But anyway, this, and 6/8,
>
> Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Great, thanks.

Stefano pointed out some "development process" terminology leaking into 
the comment on the last patch -- I'll clean that up, add in some 
comments about the fragile accounting, and send v5.  That should be it 
for this series, I think.
 -George

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