Re: [Qemu-devel] [RFC Patch] xen/pt: Emulate FLR capability

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Chao Gao <chao.gao@intel.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	qemu-devel@nongnu.org, Paul Durrant <paul.durrant@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Anthony Perard <anthony.perard@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [Qemu-devel] [RFC Patch] xen/pt: Emulate FLR capability
Date: Thu, 29 Aug 2019 12:21:11 +0200	[thread overview]
Message-ID: <20190829102059.bk4l7itydj73d3ua@Air-de-Roger> (raw)
In-Reply-To: <1567069347-22841-1-git-send-email-chao.gao@intel.com>

On Thu, Aug 29, 2019 at 05:02:27PM +0800, Chao Gao wrote:
> Currently, for a HVM on Xen, no reset method is virtualized. So in a VM's
> perspective, assigned devices cannot be reset. But some devices rely on PCI
> reset to recover from hardware hangs. When being assigned to a VM, those
> devices cannot be reset and won't work any longer if a hardware hang occurs.
> We have to reboot VM to trigger PCI reset on host to recover the device.
>
> This patch exposes FLR capability to VMs if the assigned device can be reset on
> host. When VM initiates an FLR to a device, qemu cleans up the device state,
> (including disabling of intx and/or MSI and unmapping BARs from guest, deleting
> emulated registers), then initiate PCI reset through 'reset' knob under the
> device's sysfs, finally initialize the device again.

I think you likely need to deassign the device from the VM, perform
the reset, and then assign the device again, so that there's no Xen
internal state carried over prior to the reset?

Thanks, Roger.