Re: [PATCH v7 5/6] PCI: Allow drivers to control VF BAR size

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Wed, 2 Apr 2025, Michał Winiarski wrote:

> Drivers could leverage the fact that the VF BAR MMIO reservation is
> created for total number of VFs supported by the device by resizing the
> BAR to larger size when smaller number of VFs is enabled.
> 
> Add a pci_iov_vf_bar_set_size() function to control the size and a
> pci_iov_vf_bar_get_sizes() helper to get the VF BAR sizes that will
> allow up to num_vfs to be successfully enabled with the current
> underlying reservation size.
> 
> Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
> ---
>  drivers/pci/iov.c   | 69 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci.h |  6 ++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 2fafbd6a998f0..8a62049b56b41 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -1313,3 +1313,72 @@ int pci_sriov_configure_simple(struct pci_dev *dev, int nr_virtfn)
>  	return nr_virtfn;
>  }
>  EXPORT_SYMBOL_GPL(pci_sriov_configure_simple);
> +
> +/**
> + * pci_iov_vf_bar_set_size - set a new size for a VF BAR
> + * @dev: the PCI device
> + * @resno: the resource number
> + * @size: new size as defined in the spec (0=1MB, 31=128TB)
> + *
> + * Set the new size of a VF BAR that supports VF resizable BAR capability.
> + * Unlike pci_resize_resource(), this does not cause the resource that
> + * reserves the MMIO space (originally up to total_VFs) to be resized, which
> + * means that following calls to pci_enable_sriov() can fail if the resources
> + * no longer fit.
> + *
> + * Return: 0 on success, or negative on failure.
> + */
> +int pci_iov_vf_bar_set_size(struct pci_dev *dev, int resno, int size)
> +{
> +	int ret;
> +	u32 sizes;

Please reverse the order of these variables.

> +
> +	if (!pci_resource_is_iov(resno))
> +		return -EINVAL;
> +
> +	if (pci_iov_is_memory_decoding_enabled(dev))
> +		return -EBUSY;
> +
> +	sizes = pci_rebar_get_possible_sizes(dev, resno);
> +	if (!sizes)
> +		return -ENOTSUPP;
> +
> +	if (!(sizes & BIT(size)))

Add include for BIT().

Although adding a helper like this would be helpful for multiple callers:

@@ -3780,6 +3780,88 @@ u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar)
 }
 EXPORT_SYMBOL(pci_rebar_get_possible_sizes);
 
+/**
+ * pci_rebar_size_supported - check if size is supported for a resizable BAR
+ * @pdev: PCI device
+ * @bar: BAR to check
+ * @size: size as defined in the spec (0=1MB, 31=128TB)
+ *
+ * Return: %0 if @size is supported for @bar,
+ *        %-EINVAL if @size is not supported,
+ *        %-ENOTSUPP if @bar is not resizable.
+ */
+int pci_rebar_size_supported(struct pci_dev *pdev, int bar, int size)
+{
+       u64 sizes;
+
+       sizes = pci_rebar_get_possible_sizes(pdev, bar);
+       if (!sizes)
+               return -ENOTSUPP;
+
+       return BIT(size) & sizes ? 0 : -EINVAL;
+}
+EXPORT_SYMBOL_GPL(pci_rebar_size_supported);

(Yes, I've some rebar helpers pending so this is extract from that.)

> +		return -EINVAL;
> +
> +	ret = pci_rebar_set_size(dev, resno, size);
> +	if (ret)
> +		return ret;
> +
> +	pci_iov_resource_set_size(dev, resno, pci_rebar_size_to_bytes(size));
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_iov_vf_bar_set_size);
> +
> +/**
> + * pci_iov_vf_bar_get_sizes - get VF BAR sizes allowing to create up to num_vfs
> + * @dev: the PCI device
> + * @resno: the resource number
> + * @num_vfs: number of VFs
> + *
> + * Get the sizes of a VF resizable BAR that can accommodate @num_vfs within
> + * the currently assigned size of the resource @resno.
> + *
> + * Return: A bitmask of sizes in format defined in the spec (bit 0=1MB,
> + * bit 31=128TB).
> + */
> +u32 pci_iov_vf_bar_get_sizes(struct pci_dev *dev, int resno, int num_vfs)
> +{
> +	resource_size_t vf_len = pci_resource_len(dev, resno);
> +	u32 sizes;
> +
> +	if (!num_vfs)
> +		return 0;
> +
> +	do_div(vf_len, num_vfs);

Add include for do_div().

> +	sizes = (roundup_pow_of_two(vf_len + 1) - 1) >> ilog2(SZ_1M);

Doesn't resource_size() already do that + 1 so why is a second one needed 
here?

Add include for ilog() and SZ_*.

> +
> +	return sizes & pci_rebar_get_possible_sizes(dev, resno);
> +}
> +EXPORT_SYMBOL_GPL(pci_iov_vf_bar_get_sizes);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 0e8e3fd77e967..c8708f3749757 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2389,6 +2389,8 @@ int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>  int pci_sriov_get_totalvfs(struct pci_dev *dev);
>  int pci_sriov_configure_simple(struct pci_dev *dev, int nr_virtfn);
>  resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno);
> +int pci_iov_vf_bar_set_size(struct pci_dev *dev, int resno, int size);
> +u32 pci_iov_vf_bar_get_sizes(struct pci_dev *dev, int resno, int num_vfs);
>  void pci_vf_drivers_autoprobe(struct pci_dev *dev, bool probe);
>  
>  /* Arch may override these (weak) */
> @@ -2441,6 +2443,10 @@ static inline int pci_sriov_get_totalvfs(struct pci_dev *dev)
>  #define pci_sriov_configure_simple	NULL
>  static inline resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno)
>  { return 0; }
> +static inline int pci_iov_vf_bar_set_size(struct pci_dev *dev, int resno, int size)
> +{ return -ENODEV; }
> +static inline u32 pci_iov_vf_bar_get_sizes(struct pci_dev *dev, int resno, int num_vfs)
> +{ return 0; }
>  static inline void pci_vf_drivers_autoprobe(struct pci_dev *dev, bool probe) { }
>  #endif
>  
> 

-- 
 i.