Re: bhyve: disable msi and msix on virtio reset?

[Tycho Nightingale via freebsd-virtualization]

Hi,

On Jul 12, 2016, at 7:38 PM, Peter Grehan  wrote:

>> Yes, writing 0 to the status resister should reset the device
>> including all PCIE state.  This implies that vi_reset_dev() needs to
>> take the proper actions to bring the associated pci_devinst (which
>> from the guest’s perspective isn’t a discrete element) back to it’s
>> reset state too.
> 
> I'm not sure if the reset also hits PCIe state, if you're counting config 
> space as part of that (e.g. BAR contents). As an example, the FreeBSD guest 
> virtio code doesn't do any config space saves/restores around a reset.

This is one of those ambiguities in the virtio spec wherein the canonical 
implementation (qemu) becomes the de facto standard.  I see in illumos driver 
that only a virtio-reset is performed in the quiesce entry point.  On qemu Is 
this sufficient on qemu to support warm rest?  If so then perhaps we should 
only clear the capabilities (MSIX) and not the BARs.

Tycho
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Re: bhyve: disable msi and msix on virtio reset?

[Peter Grehan]

Hi Tycho,


Yes, writing 0 to the status resister should reset the device
including all PCIE state.  This implies that vi_reset_dev() needs to
take the proper actions to bring the associated pci_devinst (which
from the guest’s perspective isn’t a discrete element) back to it’s
reset state too.


 I'm not sure if the reset also hits PCIe state, if you're counting 
config space as part of that (e.g. BAR contents). As an example, the 
FreeBSD guest virtio code doesn't do any config space saves/restores 
around a reset.


later,

Peter.
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Re: bhyve: disable msi and msix on virtio reset?

[Tycho Nightingale via freebsd-virtualization]

Hi,

Yes, writing 0 to the status resister should reset the device including all 
PCIE state.  This implies that vi_reset_dev() needs to take the proper actions 
to bring the associated pci_devinst (which from the guest’s perspective isn’t a 
discrete element) back to it’s reset state too.

Tycho

On Jul 12, 2016, at 8:27 AM, Andriy Gapon  wrote:

> 
> A write of a zero to VTCFG_R_STATUS initiates a virtio device reset via
> vc_reset.  Typically this means a call to vi_reset_dev() which resets a
> bunch of fields in virtio_softc, but does not touch a corresponding
> pci_devinst (hanging off vs_pi) at all.  Among other things this means
> that PCI MSI and MSI-X states remain unchanged.  One of the consequences
> is that we keep using virtio_config_size of 24 if MSI-X is enabled.
> 
> Should the virtio status reset also reset the PCI state?
> 
> One practical problem that I see is with illumos fast reboot where the
> illumos virtio driver assumes that the status reset is sufficient to
> return a device to a state like after a clean (full) reboot.
> 
> Thank you.
> -- 
> Andriy Gapon
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bhyve: disable msi and msix on virtio reset?

[Andriy Gapon]

A write of a zero to VTCFG_R_STATUS initiates a virtio device reset via
vc_reset.  Typically this means a call to vi_reset_dev() which resets a
bunch of fields in virtio_softc, but does not touch a corresponding
pci_devinst (hanging off vs_pi) at all.  Among other things this means
that PCI MSI and MSI-X states remain unchanged.  One of the consequences
is that we keep using virtio_config_size of 24 if MSI-X is enabled.

Should the virtio status reset also reset the PCI state?

One practical problem that I see is with illumos fast reboot where the
illumos virtio driver assumes that the status reset is sufficient to
return a device to a state like after a clean (full) reboot.

Thank you.
-- 
Andriy Gapon
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