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Re: [PATCH 4/4] pci: Compare function number and ARI next function numbe
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH 4/4] pci: Compare function number and ARI next function number |
Date: |
Sun, 2 Jul 2023 04:55:44 -0400 |
On Sun, Jul 02, 2023 at 05:46:38PM +0900, Akihiko Odaki wrote:
> On 2023/07/02 13:58, Michael S. Tsirkin wrote:
> > On Sat, Jul 01, 2023 at 04:01:22PM +0900, Akihiko Odaki wrote:
> > > The function number must be lower than the next function number
> > > advertised with ARI.
> > >
> > > Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> >
> > I don't get this logic at all - where is the limitation coming from?
> >
> > All I see in the spec is:
> > Next Function Number - With non-VFs, this field indicates the Function
> > Number of the next higher
> > numbered Function in the Device, or 00h if there are no higher numbered
> > Functions. Function 0 starts
> > this linked list of Functions.
> > The presence of Shadow Functions does not affect this field.
> > For VFs, this field is undefined since VFs are located using First VF
> > Offset (see § Section 9.3.3.9 ) and VF
> > Stride (see § Section 9.3.3.10 ).
> >
> > and
> >
> > To improve the enumeration performance and create a more deterministic
> > solution, software can
> > enumerate Functions through a linked list of Function Numbers. The next
> > linked list element is
> > communicated through each Function’s ARI Capability Register.
> > i. Function 0 acts as the head of a linked list of Function Numbers.
> > Software detects a
> > non-Zero Next Function Number field within the ARI Capability Register
> > as the next
> > Function within the linked list. Software issues a configuration probe
> > using the Bus Number
> > captured by the Device and the Function Number derived from the ARI
> > Capability Register
> > to locate the next associated Function’s configuration space.
> > ii. Function Numbers may be sparse and non-sequential in their
> > consumption by an ARI
> > Device.
>
> The statement "With non-VFs, this field indicates the Function Number of the
> next higher numbered Function in the Device, or 00h if there are no higher
> numbered Functions." implies the Function Number of the device should be
> lower than the value advertised by the field (for non-VFs; this patch does
> not check if it's VF or not.)
Now I get it. Good point! I'd say if we want this check we should add
it in pcie_ari_init, making that return int.
But for now it's dead code since your are changing it to 0.
So maybe a comment in pcie_ari_init is enough:
/*
* Note: nextfn must be the Function Number of the
* next higher numbered Function in the Device, or 00h if there are no higher
* numbered Functions.
* TODO: validate this.
*/
> >
> >
> >
> >
> >
> > > ---
> > > hw/pci/pci.c | 15 +++++++++++++++
> > > 1 file changed, 15 insertions(+)
> > >
> > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > > index e2eb4c3b4a..568665ee42 100644
> > > --- a/hw/pci/pci.c
> > > +++ b/hw/pci/pci.c
> > > @@ -2059,6 +2059,8 @@ static void pci_qdev_realize(DeviceState *qdev,
> > > Error **errp)
> > > Error *local_err = NULL;
> > > bool is_default_rom;
> > > uint16_t class_id;
> > > + uint16_t ari;
> > > + uint16_t nextfn;
> > > /*
> > > * capped by systemd (see: udev-builtin-net_id.c)
> > > @@ -2121,6 +2123,19 @@ static void pci_qdev_realize(DeviceState *qdev,
> > > Error **errp)
> > > }
> > > }
> > > + if (pci_is_express(pci_dev)) {
> > > + ari = pcie_find_capability(pci_dev, PCI_EXT_CAP_ID_ARI);
> > > + if (ari) {
> > > + nextfn = (pci_get_long(pci_dev->config + ari + PCI_ARI_CAP)
> > > >> 8) & 0xff;
> > > + if (nextfn && (pci_dev->devfn & 0xff) >= nextfn) {
> > > + error_setg(errp, "PCI: function number %u is not lower
> > > than ARI next function number %u",
> > > + pci_dev->devfn & 0xff, nextfn);
> > > + pci_qdev_unrealize(DEVICE(pci_dev));
> > > + return;
> > > + }
> > > + }
> > > + }
> > > +
> > > if (pci_dev->failover_pair_id) {
> > > if (!pci_bus_is_express(pci_get_bus(pci_dev))) {
> > > error_setg(errp, "failover primary device must be on "
> > > --
> > > 2.41.0
> >
Re: [PATCH 4/4] pci: Compare function number and ARI next function number, Ani Sinha, 2023/07/11
Re: [PATCH 0/4] pci: Compare function number and ARI next function number, Michael S. Tsirkin, 2023/07/02