Re: [Xen-devel] Limitation in HVM physmap

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-10-18 at 16:07 +0100, Wei Liu wrote:
> On Fri, Oct 18, 2013 at 04:04:17PM +0100, Wei Liu wrote:
> > On Fri, Oct 18, 2013 at 03:59:10PM +0100, Ian Campbell wrote:
> > [...]
> > > > > 
> > > > 
> > > > During OVMF initialization:
> > > > 
> > > > (d28) PciBus: Resource Map for Root Bridge PciRoot(0x0)                 
> > > >         
> > > > (d28) Type =   Io16; Base = 0xC000;     Length = 0x1000;        
> > > > Alignment = 0xFFF
> > > > (d28)  Base = 0xC000;   Length = 0x100; Alignment = 0xFF;       Owner = 
> > > > PCI  [00|04|
> > > > (d28)  Base = 0xC100;   Length = 0x100; Alignment = 0xFF;       Owner = 
> > > > PCI  [00|03|
> > > > (d28)  Base = 0xC200;   Length = 0x10;  Alignment = 0xF;        Owner = 
> > > > PCI  [00|01|
> > > > (d28) Type =  Mem32; Base = 0x80000000; Length = 0x3100000;     
> > > > Alignment = 0x1FFFFF
> > > > (d28)  Base = 0x80000000;       Length = 0x2000000;     Alignment = 
> > > > 0x1FFFFFF;  Owne
> > > > (d28) |02|00:10] 
> > > > 
> > > > Later when Linux loads EFIFB driver:
> > > > [    2.628264] efifb: framebuffer at 0x80000000, mapped to
> > > > 0xffffc90000100000, using 1876k, total 1875k
> > > > [    2.646827] efifb: mode is 800x600x32, linelength=3200, pages=1
> > > > [    2.658833] efifb: scrolling: redraw
> > > > [    2.666342] efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0
> > > > 
> > > > 0xf0000000 is mapped by:
> > > 
> > > What hardware is backing the framebuffer at 0x80000000? It doesn't
> > > appear to be this cirrus device.
> > > 
> > 
> > Looking that the "Resource Map for Root Bridge" 0x8000000 is backed by
> > 00:02:00 (trancated above) and 00:02.0 is also owned by Cirrus Logic
> > driver...
> > 
> > > Does this VM have two graphics cards and therefore two drivers (efifb
> > > and cirrusfb/vesafb/etc)?
> > > 
> > > If there are two gfx cards then there should be two framebuffers and
> > > therefore no mfn sharing in the p2m, although you would probably be
> > > better off arranging for their to only one gfx card...
> > > 
> > 
> > AIUI there is only one card.
> > 
> 
> FWIW there's a QEMU Cirrus Logic card driver in OVMF which drives the
> emulated card.

So is the bug that both OVMF and Linux are trying to drive the card?
They can't both do it, unless OVMF is even more magic than I thought...

Ian.



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