Re: ARM: PCI devices emulation broken with KVM due to cache issue

From: Christoffer Dall <christoffer.dall@linaro.org>
To: "Jérémy Fanguède" <j.fanguede@virtualopensystems.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	VirtualOpenSystems Technical Team <tech@virtualopensystems.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: ARM: PCI devices emulation broken with KVM due to cache issue
Date: Fri, 17 Apr 2015 16:06:48 +0200	[thread overview]
Message-ID: <20150417140648.GJ6186@cbox> (raw)
In-Reply-To: <CAGE1QJo-waQgNyy4XG6Ecqeg3yXH_o4EFuqX+mzj0_66X-ghXQ@mail.gmail.com>

On Fri, Apr 17, 2015 at 03:48:35PM +0200, Jérémy Fanguède wrote:
> On Fri, Apr 17, 2015 at 11:29 AM, Christoffer Dall
> <christoffer.dall@linaro.org> 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
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