VF MMIO resource reservation, either created by system firmware and
inherited by Linux PCI subsystem or created by the subsystem itself,
contains enough space to fit the BAR of all SR-IOV Virtual Functions
that can potentially be created (total VFs supported by the device).
This can be leveraged when the device is exposing lower than optimal BAR
size as a default, allowing access to the entire resource when lower
number of VFs are created.
It is achieved by dynamically resizing the BAR to largest possible value
that allows to fit all newly created VFs within the original resource
boundary.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
---
 drivers/pci/iov.c   | 92 ++++++++++++++++++++++++++++++++++++++++++++-
 drivers/pci/pci.h   |  1 +
 include/linux/pci.h |  3 ++
 3 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 591a3eae1618a..f9071c1cfe9ee 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -174,6 +174,86 @@ bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev)
 	return cmd & PCI_SRIOV_CTRL_MSE;
 }
 
+static void pci_iov_resource_do_extend(struct pci_dev *dev, int resno, u16 num_vfs)
+{
+	resource_size_t size;
+	int ret, old, i;
+	u32 sizes;
+
+	pci_config_pm_runtime_get(dev);
+
+	if (pci_iov_is_memory_decoding_enabled(dev)) {
+		ret = -EBUSY;
+		goto err;
+	}
+
+	sizes = pci_rebar_get_possible_sizes(dev, resno);
+	if (!sizes) {
+		ret = -ENOTSUPP;
+		goto err;
+	}
+
+	old = pci_rebar_get_current_size(dev, resno);
+	if (old < 0) {
+		ret = old;
+		goto err;
+	}
+
+	while (sizes > 0) {
+		i = __fls(sizes);
+		size = pci_rebar_size_to_bytes(i);
+		if (size * num_vfs <= pci_resource_len(dev, resno)) {
+			if (i != old) {
+				ret = pci_rebar_set_size(dev, resno, size);
+				if (ret)
+					goto err;
+
+				pci_iov_resource_set_size(dev, resno, size);
+				pci_iov_update_resource(dev, resno);
+			}
+			break;
+		}
+		sizes &= ~BIT(i);
+	}
+
+	pci_config_pm_runtime_put(dev);
+
+	return;
+
+err:
+	pci_warn(dev, "Failed to extend %s: %d\n",
+		 pci_resource_name(dev, resno), ret);
+
+	pci_config_pm_runtime_put(dev);
+}
+
+static void pci_iov_resource_do_restore(struct pci_dev *dev, int resno)
+{
+	if (dev->sriov->rebar_extend[resno - PCI_IOV_RESOURCES])
+		pci_iov_resource_do_extend(dev, resno, dev->sriov->total_VFs);
+}
+
+int pci_iov_resource_extend(struct pci_dev *dev, int resno, bool enable)
+{
+	if (!pci_resource_is_iov(resno)) {
+		pci_warn(dev, "%s is not an IOV resource\n",
+			 pci_resource_name(dev, resno));
+
+		return -ENODEV;
+	}
+
+	if (!pci_rebar_get_possible_sizes(dev, resno))
+		return -ENOTSUPP;
+
+	if (!enable)
+		pci_iov_resource_do_restore(dev, resno);
+
+	dev->sriov->rebar_extend[resno - PCI_IOV_RESOURCES] = enable;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_iov_resource_extend);
+
 static void pci_read_vf_config_common(struct pci_dev *virtfn)
 {
 	struct pci_dev *physfn = virtfn->physfn;
@@ -438,7 +518,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
 				  const char *buf, size_t count)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
-	int ret = 0;
+	int i, ret = 0;
 	u16 num_vfs;
 
 	if (kstrtou16(buf, 0, &num_vfs) < 0)
@@ -480,6 +560,11 @@ static ssize_t sriov_numvfs_store(struct device *dev,
 		goto exit;
 	}
 
+	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
+		if (pdev->sriov->rebar_extend[i])
+			pci_iov_resource_do_extend(pdev, i + PCI_IOV_RESOURCES, num_vfs);
+	}
+
 	ret = pdev->driver->sriov_configure(pdev, num_vfs);
 	if (ret < 0)
 		goto exit;
@@ -874,8 +959,13 @@ static int sriov_init(struct pci_dev *dev, int pos)
 
 static void sriov_release(struct pci_dev *dev)
 {
+	int i;
+
 	BUG_ON(dev->sriov->num_VFs);
 
+	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++)
+		pci_iov_resource_do_restore(dev, i + PCI_IOV_RESOURCES);
+
 	if (dev != dev->sriov->dev)
 		pci_dev_put(dev->sriov->dev);
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index e15fd8fe0f81f..57e79f75e4c8f 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -403,6 +403,7 @@ struct pci_sriov {
 	u16		subsystem_vendor; /* VF subsystem vendor */
 	u16		subsystem_device; /* VF subsystem device */
 	resource_size_t	barsz[PCI_SRIOV_NUM_BARS];	/* VF BAR size */
+	bool		rebar_extend[PCI_SRIOV_NUM_BARS];	/* Resize VF BAR */
 	bool		drivers_autoprobe; /* Auto probing of VFs by driver */
 };
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 573b4c4c2be61..023c0fa1dd9f2 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2371,6 +2371,7 @@ 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_resource_extend(struct pci_dev *dev, int resno, bool enable);
 void pci_vf_drivers_autoprobe(struct pci_dev *dev, bool probe);
 
 /* Arch may override these (weak) */
@@ -2423,6 +2424,8 @@ 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_resource_extend(struct pci_dev *dev, int resno, bool enable)
+{ return -ENODEV; }
 static inline void pci_vf_drivers_autoprobe(struct pci_dev *dev, bool probe) { }
 #endif
 
-- 
2.47.0

On Thu, Oct 10, 2024 at 12:32:02PM +0200, Michał Winiarski wrote:
> VF MMIO resource reservation, either created by system firmware and
> inherited by Linux PCI subsystem or created by the subsystem itself,
> contains enough space to fit the BAR of all SR-IOV Virtual Functions
> that can potentially be created (total VFs supported by the device).

It's *possible* that this is true, but there's no guarantee that
firmware has assigned enough space for all BARs of all possible VFs.

> This can be leveraged when the device is exposing lower than optimal BAR
> size as a default, allowing access to the entire resource when lower
> number of VFs are created.
> It is achieved by dynamically resizing the BAR to largest possible value
> that allows to fit all newly created VFs within the original resource
> boundary.

Add blank lines between paragraphs.

This log doesn't actually say what the patch does.  It describes a
possible configuration and ways that it may be used, and even *how*
something might be done, but something along the lines of the subject
line should be included in the commit log.

> +static void pci_iov_resource_do_extend(struct pci_dev *dev, int resno, u16 num_vfs)

Please wrap to fit in 80 columns like the rest of the file.

> +int pci_iov_resource_extend(struct pci_dev *dev, int resno, bool enable)

Please add kerneldoc here to help users of this exported function.

> @@ -480,6 +560,11 @@ static ssize_t sriov_numvfs_store(struct device *dev,
>  		goto exit;
>  	}
>  
> +	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
> +		if (pdev->sriov->rebar_extend[i])
> +			pci_iov_resource_do_extend(pdev, i + PCI_IOV_RESOURCES, num_vfs);

Wrap to fit in 80 columns.

Bjorn