Re: [PATCH 04/15] pcie: Add callback preceding SR-IOV VFs update

[Lukasz Maniak <lukasz.maniak@linux.intel.com>]

On Fri, Oct 15, 2021 at 01:30:32PM -0400, Michael S. Tsirkin wrote:
> On Fri, Oct 15, 2021 at 06:24:14PM +0200, Lukasz Maniak wrote:
> > On Wed, Oct 13, 2021 at 05:10:35AM -0400, Michael S. Tsirkin wrote:
> > > On Tue, Oct 12, 2021 at 06:06:46PM +0200, Lukasz Maniak wrote:
> > > > On Tue, Oct 12, 2021 at 03:25:12AM -0400, Michael S. Tsirkin wrote:
> > > > > On Thu, Oct 07, 2021 at 06:23:55PM +0200, Lukasz Maniak wrote:
> > > > > > PCIe devices implementing SR-IOV may need to perform certain actions
> > > > > > before the VFs are unrealized or vice versa.
> > > > > > 
> > > > > > Signed-off-by: Lukasz Maniak <lukasz.maniak@linux.intel.com>
> > > > > 
> > > > > Callbacks are annoying and easy to misuse though.
> > > > > VFs are enabled through a config cycle, we generally just
> > > > > have devices invoke the capability handler.
> > > > > E.g.
> > > > > 
> > > > > static void pci_bridge_dev_write_config(PCIDevice *d,
> > > > >                                         uint32_t address, uint32_t val, int len)
> > > > > {
> > > > >     pci_bridge_write_config(d, address, val, len);
> > > > >     if (msi_present(d)) {
> > > > >         msi_write_config(d, address, val, len);
> > > > >     }
> > > > > }
> > > > > 
> > > > > this makes it easy to do whatever you want before/after
> > > > > the write. You can also add a helper to check
> > > > > that SRIOV is being enabled/disabled if necessary.
> > > > > 
> > > > > > ---
> > > > > >  docs/pcie_sriov.txt         |  2 +-
> > > > > >  hw/pci/pcie_sriov.c         | 14 +++++++++++++-
> > > > > >  include/hw/pci/pcie_sriov.h |  8 +++++++-
> > > > > >  3 files changed, 21 insertions(+), 3 deletions(-)
> > > > > > 
> > > > > > diff --git a/docs/pcie_sriov.txt b/docs/pcie_sriov.txt
> > > > > > index f5e891e1d4..63ca1a7b8e 100644
> > > > > > --- a/docs/pcie_sriov.txt
> > > > > > +++ b/docs/pcie_sriov.txt
> > > > > > @@ -57,7 +57,7 @@ setting up a BAR for a VF.
> > > > > >        /* Add and initialize the SR/IOV capability */
> > > > > >        pcie_sriov_pf_init(d, 0x200, "your_virtual_dev",
> > > > > >                         vf_devid, initial_vfs, total_vfs,
> > > > > > -                       fun_offset, stride);
> > > > > > +                       fun_offset, stride, pre_vfs_update_cb);
> > > > > >  
> > > > > >        /* Set up individual VF BARs (parameters as for normal BARs) */
> > > > > >        pcie_sriov_pf_init_vf_bar( ... )
> > > > > > diff --git a/hw/pci/pcie_sriov.c b/hw/pci/pcie_sriov.c
> > > > > > index 501a1ff433..cac2aee061 100644
> > > > > > --- a/hw/pci/pcie_sriov.c
> > > > > > +++ b/hw/pci/pcie_sriov.c
> > > > > > @@ -30,7 +30,8 @@ static void unregister_vfs(PCIDevice *dev);
> > > > > >  void pcie_sriov_pf_init(PCIDevice *dev, uint16_t offset,
> > > > > >                          const char *vfname, uint16_t vf_dev_id,
> > > > > >                          uint16_t init_vfs, uint16_t total_vfs,
> > > > > > -                        uint16_t vf_offset, uint16_t vf_stride)
> > > > > > +                        uint16_t vf_offset, uint16_t vf_stride,
> > > > > > +                        SriovVfsUpdate pre_vfs_update)
> > > > > >  {
> > > > > >      uint8_t *cfg = dev->config + offset;
> > > > > >      uint8_t *wmask;
> > > > > > @@ -41,6 +42,7 @@ void pcie_sriov_pf_init(PCIDevice *dev, uint16_t offset,
> > > > > >      dev->exp.sriov_pf.num_vfs = 0;
> > > > > >      dev->exp.sriov_pf.vfname = g_strdup(vfname);
> > > > > >      dev->exp.sriov_pf.vf = NULL;
> > > > > > +    dev->exp.sriov_pf.pre_vfs_update = pre_vfs_update;
> > > > > >  
> > > > > >      pci_set_word(cfg + PCI_SRIOV_VF_OFFSET, vf_offset);
> > > > > >      pci_set_word(cfg + PCI_SRIOV_VF_STRIDE, vf_stride);
> > > > > > @@ -180,6 +182,11 @@ static void register_vfs(PCIDevice *dev)
> > > > > >      assert(dev->exp.sriov_pf.vf);
> > > > > >  
> > > > > >      trace_sriov_register_vfs(SRIOV_ID(dev), num_vfs);
> > > > > > +
> > > > > > +    if (dev->exp.sriov_pf.pre_vfs_update) {
> > > > > > +        dev->exp.sriov_pf.pre_vfs_update(dev, dev->exp.sriov_pf.num_vfs, num_vfs);
> > > > > > +    }
> > > > > > +
> > > > > >      for (i = 0; i < num_vfs; i++) {
> > > > > >          dev->exp.sriov_pf.vf[i] = register_vf(dev, devfn, dev->exp.sriov_pf.vfname, i);
> > > > > >          if (!dev->exp.sriov_pf.vf[i]) {
> > > > > > @@ -198,6 +205,11 @@ static void unregister_vfs(PCIDevice *dev)
> > > > > >      uint16_t i;
> > > > > >  
> > > > > >      trace_sriov_unregister_vfs(SRIOV_ID(dev), num_vfs);
> > > > > > +
> > > > > > +    if (dev->exp.sriov_pf.pre_vfs_update) {
> > > > > > +        dev->exp.sriov_pf.pre_vfs_update(dev, dev->exp.sriov_pf.num_vfs, 0);
> > > > > > +    }
> > > > > > +
> > > > > >      for (i = 0; i < num_vfs; i++) {
> > > > > >          PCIDevice *vf = dev->exp.sriov_pf.vf[i];
> > > > > >          object_property_set_bool(OBJECT(vf), "realized", false, &local_err);
> > > > > > diff --git a/include/hw/pci/pcie_sriov.h b/include/hw/pci/pcie_sriov.h
> > > > > > index 0974f00054..9ab48b79c0 100644
> > > > > > --- a/include/hw/pci/pcie_sriov.h
> > > > > > +++ b/include/hw/pci/pcie_sriov.h
> > > > > > @@ -13,11 +13,16 @@
> > > > > >  #ifndef QEMU_PCIE_SRIOV_H
> > > > > >  #define QEMU_PCIE_SRIOV_H
> > > > > >  
> > > > > > +typedef void (*SriovVfsUpdate)(PCIDevice *dev, uint16_t prev_num_vfs,
> > > > > > +                               uint16_t num_vfs);
> > > > > > +
> > > > > >  struct PCIESriovPF {
> > > > > >      uint16_t num_vfs;           /* Number of virtual functions created */
> > > > > >      uint8_t vf_bar_type[PCI_NUM_REGIONS];  /* Store type for each VF bar */
> > > > > >      const char *vfname;         /* Reference to the device type used for the VFs */
> > > > > >      PCIDevice **vf;             /* Pointer to an array of num_vfs VF devices */
> > > > > > +
> > > > > > +    SriovVfsUpdate pre_vfs_update;  /* Callback preceding VFs count change */
> > > > > >  };
> > > > > >  
> > > > > >  struct PCIESriovVF {
> > > > > > @@ -28,7 +33,8 @@ struct PCIESriovVF {
> > > > > >  void pcie_sriov_pf_init(PCIDevice *dev, uint16_t offset,
> > > > > >                          const char *vfname, uint16_t vf_dev_id,
> > > > > >                          uint16_t init_vfs, uint16_t total_vfs,
> > > > > > -                        uint16_t vf_offset, uint16_t vf_stride);
> > > > > > +                        uint16_t vf_offset, uint16_t vf_stride,
> > > > > > +                        SriovVfsUpdate pre_vfs_update);
> > > > > >  void pcie_sriov_pf_exit(PCIDevice *dev);
> > > > > >  
> > > > > >  /* Set up a VF bar in the SR/IOV bar area */
> > > > > > -- 
> > > > > > 2.25.1
> > > > >
> > > > 
> > > > Hi Michael,
> > > > 
> > > > A custom config_write callback was the first approach we used.
> > > > However, once implemented, we realized it looks the same as the
> > > > pcie_sriov_config_write function. To avoid code duplication and
> > > > interfering with the internal SR-IOV structures for purposes of NVMe,
> > > > we opted for this callback prior to the VFs update.
> > > > After all, we have callbacks in both approaches, config_write and the
> > > > added pre_vfs_update, so both are prone to misuse.
> > > > 
> > > > But I agree it may not be a good moment yet to add a new API
> > > > specifically for SR-IOV functionality, as NVMe will be the first device
> > > > to use it.
> > > > 
> > > > CCing Knut, perhaps as the author of SR-IOV you have some thoughts on
> > > > how the device notification of an upcoming VFs update would be handled.
> > > > 
> > > > Thanks,
> > > > Lukasz
> > > 
> > > So just split it up?
> > > 
> > > void pcie_sriov_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > > {
> > >     uint32_t off;
> > >     uint16_t sriov_cap = dev->exp.sriov_cap;
> > > 
> > >     if (!sriov_cap || address < sriov_cap) {
> > >         return;
> > >     }
> > >     off = address - sriov_cap;
> > >     if (off >= PCI_EXT_CAP_SRIOV_SIZEOF) {
> > >         return;
> > >     }
> > >     
> > >     trace_sriov_config_write(SRIOV_ID(dev), off, val, len);
> > >         
> > >     if (range_covers_byte(off, len, PCI_SRIOV_CTRL)) {
> > >         if (dev->exp.sriov_pf.num_vfs) {
> > >             if (!(val & PCI_SRIOV_CTRL_VFE)) {
> > >                 unregister_vfs(dev);
> > >             }
> > >         } else {
> > >             if (val & PCI_SRIOV_CTRL_VFE) {
> > >                 register_vfs(dev);
> > >             }
> > >         }
> > >     }
> > > }
> > > 
> > > 
> > > Would become:
> > > 
> > > bool
> > >  pcie_sriov_is_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > > {
> > >     uint32_t off;
> > >     uint16_t sriov_cap = dev->exp.sriov_cap;
> > > 
> > >     if (!sriov_cap || address < sriov_cap) {
> > >         return false;
> > >     }
> > >     off = address - sriov_cap;
> > >     if (off >= PCI_EXT_CAP_SRIOV_SIZEOF) {
> > >         return false;
> > >     }
> > > }
> > > 
> > > bool
> > >  pcie_sriov_do_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > > {
> > >     trace_sriov_config_write(SRIOV_ID(dev), off, val, len);
> > >         
> > >     if (range_covers_byte(off, len, PCI_SRIOV_CTRL)) {
> > >         if (dev->exp.sriov_pf.num_vfs) {
> > >             if (!(val & PCI_SRIOV_CTRL_VFE)) {
> > >                 unregister_vfs(dev);
> > >             }
> > >         } else {
> > >             if (val & PCI_SRIOV_CTRL_VFE) {
> > >                 register_vfs(dev);
> > >             }
> > >         }
> > >     }
> > > }
> > > 
> > > 
> > > 
> > > void pcie_sriov_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > > {
> > > 	if (pcie_sriov_is_config_write(dev, address, val, len)) {
> > > 		pcie_sriov_do_config_write(dev, address, val, len);
> > > 	}
> > >     
> > > }
> > > 
> > > 
> > > Now  pcie_sriov_is_config_write and pcie_sriov_do_config_write
> > > can be reused by NVME.
> > > 
> > > -- 
> > > MST
> > > 
> > 
> > Hi Michael,
> > 
> > I extracted one condition to the helper, what do you think?
> > 
> > bool pcie_sriov_is_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > {
> >     uint32_t off;
> >     uint16_t sriov_cap = dev->exp.sriov_cap;
> > 
> >     if (!sriov_cap || address < sriov_cap) {
> >         return false;
> >     }
> >     off = address - sriov_cap;
> >     if (off >= PCI_EXT_CAP_SRIOV_SIZEOF) {
> >         return false;
> >     }
> > 
> >     if (range_covers_byte(off, len, PCI_SRIOV_CTRL)) {
> >         return true;
> >     }
> > 
> >     return false;
> > }
> > 
> > static void pcie_sriov_do_config_write(PCIDevice *dev, uint32_t address,
> >                                        uint32_t val, int len)
> > {
> >     uint32_t off = address - dev->exp.sriov_cap;
> >     trace_sriov_config_write(SRIOV_ID(dev), off, val, len);
> > 
> >     if (dev->exp.sriov_pf.num_vfs) {
> >         if (!(val & PCI_SRIOV_CTRL_VFE)) {
> >             unregister_vfs(dev);
> >         }
> >     } else {
> >         if (val & PCI_SRIOV_CTRL_VFE) {
> >             register_vfs(dev);
> >         }
> >     }
> > }
> > 
> > void pcie_sriov_config_write(PCIDevice *dev, uint32_t address, uint32_t val, int len)
> > {
> >     if (pcie_sriov_is_config_write(dev, address, val, len)) {
> >         pcie_sriov_do_config_write(dev, address, val, len);
> >     }
> > }
> 
> ok
> 
> > --
> > Lukasz
> 

Hi Michael,

After more investigation, we concluded that both pre_vfs_update callback
and pcie_sriov_config_write split are not required to perform needed
device-side actions prior to the SR-IOV state change.

Hence, we decided to drop this patch for v2.

Kind regards,
Lukasz