Re: [Qemu-devel] ARM: PCI devices emulation broken with KVM due to cache issue

[Christoffer Dall]

On Fri, Apr 17, 2015 at 03:48:35PM +0200, Jérémy Fanguède wrote:
> On Fri, Apr 17, 2015 at 11:29 AM, Christoffer Dall
> <address@hidden> wrote:
> > On Thu, Apr 16, 2015 at 06:02:27PM +0200, Paolo Bonzini wrote:
> >>
> >>
> >> On 16/04/2015 17:54, Jérémy Fangučde wrote:
> >> > The guest kernel driver of the lsi device fails to enable it correctly
> >> > with a cache error:
> >> > [...]
> >> > sym53c8xx 0000:00:01.0: enabling device (0100 -> 0103)
> >> > sym0: <895a> rev 0x0 at pci 0000:00:01.0 irq 54
> >> > sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
> >> > CACHE TEST FAILED: chip wrote 2, host read 1.
> >> > sym0: CACHE INCORRECTLY CONFIGURED.
> >> > sym0: giving up ...
> >> > [...]
> >>
> >> Note that this is just a failure in the driver self-test.  It has
> >> nothing to do with the processor cache (though there are other problems
> >> with PCI and the processor cache in KVM mode).
> >>
> >> Do not use this QEMU device.  The emulation is incomplete and it's slow.
> >>  Use virtio-scsi or megasas instead.  Still, I'm not sure that would
> >> work with KVM; as far as I know, most work on the ARM PCI host bridge
> >> was done using UEFI firmware.
> >>
> > I've been running a number of tests lately using virtio-net-pci and
> > virtio-blk-pci on XGene at it works like a charm.
> 
> It should be noted that all these devices work fine on x86 with KVM
> enabled.
> 
> Of course, not all PCI devices are affected, e.g. virtio-* devices
> work fine for me also. However, should this failure be considered
> normal with KVM on ARM, while it works on x86?
> 
> For instance, let's take the use case where there is no virtio
> alternative: USB devices (passthrough or emulated) attached to a PCI
> USB controller, how is this supposed to work with KVM on ARM?
> The only way to make usb-ehci working that I am aware, is
> with this cache hack.

As Paolo said, we know there are cache issues on KVM/ARM and we are
working through.  Patches are as always welcome ;)

-Christoffer