Re: [PATCH] PCI/IOV: Make VF config reads match PCIe 7.0 spec
From: Bjorn Helgaas
Date: Thu Sep 24 2026 - 18:59:57 EST
On Thu, Sep 10, 2026 at 10:36:48AM -0700, Logan Odell wrote:
> The revision and subsystem ID of the VFs for a given PF do not all have
> to match per 7.5.1.1.5 and 7.5.1.2.3[1]. Read these values from the
> config space instead of using cached values from VF0. Class codes and
> subsystem vendor IDs do need to match per 7.5.1.1.6 and 7.5.1.2.3. Use
> the PF's value instead of reading from the VF config space. Per
> 7.5.1.1.9, the header type for a VF should be 0, so hardcode that
> assignment.
>
> [1] https://members.pcisig.com/wg/PCI-SIG/document/previewpdf/22464
>
> Fixes: cf0921bea66c ("PCI/IOV: Use VF0 cached config registers for other VFs")
> Signed-off-by: Logan Odell <loganodell@xxxxxxxxxx>
Applied to pci/iov for v7.4, thanks!
> ---
> drivers/pci/iov.c | 25 -------------------------
> drivers/pci/pci.h | 4 ----
> drivers/pci/probe.c | 14 +++++++++-----
> 3 files changed, 9 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 9d408fb8ac25..9185934a900f 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -179,29 +179,6 @@ bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev)
> return cmd & PCI_SRIOV_CTRL_MSE;
> }
>
> -static void pci_read_vf_config_common(struct pci_dev *virtfn)
> -{
> - struct pci_dev *physfn = virtfn->physfn;
> -
> - /*
> - * Some config registers are the same across all associated VFs.
> - * Read them once from VF0 so we can skip reading them from the
> - * other VFs.
> - *
> - * PCIe r4.0, sec 9.3.4.1, technically doesn't require all VFs to
> - * have the same Revision ID and Subsystem ID, but we assume they
> - * do.
> - */
> - pci_read_config_dword(virtfn, PCI_CLASS_REVISION,
> - &physfn->sriov->class);
> - pci_read_config_byte(virtfn, PCI_HEADER_TYPE,
> - &physfn->sriov->hdr_type);
> - pci_read_config_word(virtfn, PCI_SUBSYSTEM_VENDOR_ID,
> - &physfn->sriov->subsystem_vendor);
> - pci_read_config_word(virtfn, PCI_SUBSYSTEM_ID,
> - &physfn->sriov->subsystem_device);
> -}
> -
> int pci_iov_sysfs_link(struct pci_dev *dev,
> struct pci_dev *virtfn, int id)
> {
> @@ -329,8 +306,6 @@ static struct pci_dev *pci_iov_scan_device(struct pci_dev *dev, int id,
> virtfn->physfn = pci_dev_get(dev);
> virtfn->no_command_memory = 1;
>
> - if (id == 0)
> - pci_read_vf_config_common(virtfn);
>
> rc = pci_setup_device(virtfn);
> if (rc) {
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index ba3c3fddddc2..5b3dd1adbf35 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -711,10 +711,6 @@ struct pci_sriov {
> u16 driver_max_VFs; /* Max num VFs driver supports */
> struct pci_dev *dev; /* Lowest numbered PF */
> struct pci_dev *self; /* This PF */
> - u32 class; /* VF device */
> - u8 hdr_type; /* VF header type */
> - u16 subsystem_vendor; /* VF subsystem vendor */
> - u16 subsystem_device; /* VF subsystem device */
> resource_size_t barsz[PCI_SRIOV_NUM_BARS]; /* VF BAR size */
> u16 vf_rebar_cap; /* VF Resizable BAR capability offset */
> bool drivers_autoprobe; /* Auto probing of VFs by driver */
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 27008e2ea5af..693c07cf45ff 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1888,10 +1888,14 @@ int pci_cfg_space_size(struct pci_dev *dev)
> static u32 pci_class(struct pci_dev *dev)
> {
> u32 class;
> + u8 rev;
>
> #ifdef CONFIG_PCI_IOV
> - if (dev->is_virtfn)
> - return dev->physfn->sriov->class;
> + if (dev->is_virtfn) {
> + if (pci_read_config_byte(dev, PCI_REVISION_ID, &rev))
> + rev = 0;
> + return (dev->physfn->class << 8) | rev;
> + }
> #endif
> pci_read_config_dword(dev, PCI_CLASS_REVISION, &class);
> return class;
> @@ -1901,8 +1905,8 @@ static void pci_subsystem_ids(struct pci_dev *dev, u16 *vendor, u16 *device)
> {
> #ifdef CONFIG_PCI_IOV
> if (dev->is_virtfn) {
> - *vendor = dev->physfn->sriov->subsystem_vendor;
> - *device = dev->physfn->sriov->subsystem_device;
> + *vendor = dev->physfn->subsystem_vendor;
> + pci_read_config_word(dev, PCI_SUBSYSTEM_ID, device);
> return;
> }
> #endif
> @@ -1916,7 +1920,7 @@ static u8 pci_hdr_type(struct pci_dev *dev)
>
> #ifdef CONFIG_PCI_IOV
> if (dev->is_virtfn)
> - return dev->physfn->sriov->hdr_type;
> + return 0;
> #endif
> pci_read_config_byte(dev, PCI_HEADER_TYPE, &hdr_type);
> return hdr_type;
> --
> 2.55.0.1007.g17ff1f9808-goog
>