Re: [Xen-devel] Limitation in HVM physmap

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 01/11/13 12:21, Wei Liu wrote:
> On Fri, Oct 18, 2013 at 03:20:12PM +0100, Wei Liu wrote:
> > Hi Jan, Tim and Keir
> >
> > I currently run into the limitation of HVM's physmap: one MFN can only
> > be mapped into one guest physical frame. Why is it designed like that?
> >
> > The scenario is that: when QEMU boots with OVMF (UEFI firmware), OVMF
> > will first map the framebuffer to 0x80000000, resulting the framebuffer
> > MFNs added to corresponding slots in physmap. A few moments later when
> > Linux kernel loads, it tries to map framebuffer MFNs to 0xf00000000,
> > which fails because those MFNs have already been mapped in other
> > locations. Is there a way to fix this?
> FWIW I tested this on real hardware, a Dell R710 server.
>
> dmesg:
> [   39.394807] efifb: probing for efifb
> [   39.437552] efifb: framebuffer at 0xd5800000, mapped to 0xffffc90013f00000, 
> using 1216k, total 1216k
> [   39.546549] efifb: mode is 640x480x32, linelength=2560, pages=1
> [   39.617140] efifb: scrolling: redraw
> [   39.659709] efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0
>
> lspci -vvv:
> 0b:03.0 VGA compatible controller: Matrox Electronics Systems Ltd. MGA G200eW 
> WPCM450 (rev 0a) (prog-if 00 [VGA controller])
>          Subsystem: Dell PowerEdge R710 MGA G200eW WPCM450
>          Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
> Stepping- SERR- FastB2B- DisINTx-
>          Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- 
> <MAbort- >SERR- <PERR- INTx-
>          Latency: 64 (4000ns min, 8000ns max), Cache Line Size: 64 bytes
>          Interrupt: pin A routed to IRQ 10
>          Region 0: Memory at d5800000 (32-bit, prefetchable) [size=8M]
>          Region 1: Memory at de7fc000 (32-bit, non-prefetchable) [size=16K]
>          Region 2: Memory at de800000 (32-bit, non-prefetchable) [size=8M]
>          [virtual] Expansion ROM at de000000 [disabled] [size=64K]
>          Capabilities: [dc] Power Management version 1
>                  Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA 
> PME(D0-,D1-,D2-,D3hot-,D3cold-)
>                  Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
>
> So I think the behavior of OVMF is consistent with real hardware.
Good to know - thanks for testing this.  So it looks like we'll need to 
support the same functionality for HVM guests, one way or another.
 -George

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