[PATCH v3 1/3] vfio/pci: Set up bar resources and maps in vfio_pci_core_enable()

[Matt Evans <mattev@meta.com>]

Previously BAR resource requests and the corresponding pci_iomap()
were performed on-demand and without synchronisation, which was racy.
Rather than add synchronisation, it's simplest to address this by
doing both activities from vfio_pci_core_enable().

The resource allocation and/or pci_iomap() can still fail; their
status is tracked and existing calls to vfio_pci_core_setup_barmap()
will fail in a similar way to before.  This keeps the point of failure
as observed by userspace the same, i.e. failures to request/map unused
BARs are benign.

Fixes: 7f5764e179c6 ("vfio: use vfio_pci_core_setup_barmap to map bar in mmap")
Fixes: 0d77ed3589ac0 ("vfio/pci: Pull BAR mapping setup from read-write path")
Signed-off-by: Matt Evans <mattev@meta.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 33 ++++++++++++++++++++++++++++++++
 drivers/vfio/pci/vfio_pci_rdwr.c | 29 ++++++++++++----------------
 2 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 3f8d093aacf8..eab4f2626b39 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -482,6 +482,38 @@ static int vfio_pci_core_runtime_resume(struct device *dev)
 }
 #endif /* CONFIG_PM */
 
+static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
+{
+	struct pci_dev *pdev = vdev->pdev;
+	int i;
+
+	/*
+	 * Eager-request BAR resources, and iomap.  Soft failures are
+	 * allowed, and consumers must check the barmap before use in
+	 * order to give compatible user-visible behaviour with the
+	 * previous on-demand allocation method.
+	 */
+	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
+		int bar = i + PCI_STD_RESOURCES;
+		void __iomem *io = ERR_PTR(-ENODEV);
+
+		if (pci_resource_len(pdev, i) > 0) {
+			if (pci_request_selected_regions(pdev, 1 << bar, "vfio")) {
+				pci_warn(vdev->pdev, "Failed to reserve region %d\n", bar);
+				io = ERR_PTR(-EBUSY);
+			} else {
+				io = pci_iomap(pdev, bar, 0);
+				if (!io) {
+					pci_warn(vdev->pdev, "Failed to iomap region %d\n",
+						 bar);
+					io = ERR_PTR(-ENOMEM);
+				}
+			}
+		}
+		vdev->barmap[bar] = io;
+	}
+}
+
 /*
  * The pci-driver core runtime PM routines always save the device state
  * before going into suspended state. If the device is going into low power
@@ -568,6 +600,7 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
 	if (!vfio_vga_disabled() && vfio_pci_is_vga(pdev))
 		vdev->has_vga = true;
 
+	vfio_pci_core_map_bars(vdev);
 
 	return 0;
 
diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
index 4251ee03e146..f66ad3d96481 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -200,25 +200,20 @@ EXPORT_SYMBOL_GPL(vfio_pci_core_do_io_rw);
 
 int vfio_pci_core_setup_barmap(struct vfio_pci_core_device *vdev, int bar)
 {
-	struct pci_dev *pdev = vdev->pdev;
-	int ret;
-	void __iomem *io;
-
-	if (vdev->barmap[bar])
-		return 0;
-
-	ret = pci_request_selected_regions(pdev, 1 << bar, "vfio");
-	if (ret)
-		return ret;
-
-	io = pci_iomap(pdev, bar, 0);
-	if (!io) {
-		pci_release_selected_regions(pdev, 1 << bar);
-		return -ENOMEM;
-	}
+	/*
+	 * The barmap is set up in vfio_pci_core_enable().  Callers
+	 * use this function to check that the BAR resources are
+	 * requested or that the pci_iomap() was done.
+	 */
+	if (bar < 0 || bar >= PCI_STD_NUM_BARS)
+		return -EINVAL;
 
-	vdev->barmap[bar] = io;
+	/* Did vfio_pci_core_map_bars() set it up yet? */
+	if (!vdev->barmap[bar])
+		return -ENODEV;
 
+	if (IS_ERR(vdev->barmap[bar]))
+		return PTR_ERR(vdev->barmap[bar]);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_setup_barmap);
-- 
2.47.3