[PATCH] PCI: pci-stub: accept exceptions to the ID- and class-based matching

[Laszlo Ersek]

Some systems have multiple instances of the exact same kind of PCI device
installed. When VFIO users intend to assign these devices to VMs, they
occasionally don't want to assign all of them; they'd keep a few for
host-side use. The current ID- and class-based matching in pci-stub
doesn't accommodate this use case, so users are left with either
rc.local-style host boot scripts, or QEMU wrapper scripts (which are
inferior to a pure libvirt environment).

Introduce the "except" module parameter for pci-stub. In addition to
"ids", users can specify a list of Domain:Bus:Device.Function tuples. The
tuples are parsed and saved before pci_add_dynid() is called. The pci-stub
probe function will fail for the listed devices, for the initial and all
later (explicit) binding attempts.

Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Andrei Grigore <andrei.grg@xxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Jayme Howard <g.prime@xxxxxxxxx>
Reported-by: Andrei Grigore <andrei.grg@xxxxxxxxx>
Ref: https://www.redhat.com/archives/vfio-users/2016-October/msg00121.html
Signed-off-by: Laszlo Ersek <lersek@xxxxxxxxxx>
---
 drivers/pci/pci-stub.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/drivers/pci/pci-stub.c b/drivers/pci/pci-stub.c
index 886fb3570278..120c29609c44 100644
--- a/drivers/pci/pci-stub.c
+++ b/drivers/pci/pci-stub.c
@@ -26,8 +26,44 @@ MODULE_PARM_DESC(ids, "Initial PCI IDs to add to the stub driver, format is "
 		 "\"vendor:device[:subvendor[:subdevice[:class[:class_mask]]]]\""
 		 " and multiple comma separated entries can be specified");
 
+#define MAX_EXCEPT 16
+
+static unsigned num_except;
+static struct except {
+	u16 domain;
+	u16 devid;
+} except[MAX_EXCEPT];
+
+/*
+ * Accommodate substrings like "0000:00:1c.4," MAX_EXCEPT times, with the comma
+ * replaced with '\0' in the last instance
+ */
+static char except_str[13 * MAX_EXCEPT] __initdata;
+
+module_param_string(except, except_str, sizeof except_str, 0);
+MODULE_PARM_DESC(except, "Comma-separated list of PCI addresses to except "
+		 "from the ID- and class-based binding. The address format is "
+		 "Domain:Bus:Device.Function (all components are required and "
+		 "written in hex), for example, 0000:00:1c.4. At most "
+		 __stringify(MAX_EXCEPT) " exceptions are supported.");
+
+static inline bool exception_matches(const struct except *ex,
+				     const struct pci_dev *dev)
+{
+	return ex->domain == pci_domain_nr(dev->bus) &&
+	       ex->devid == PCI_DEVID(dev->bus->number, dev->devfn);
+}
+
 static int pci_stub_probe(struct pci_dev *dev, const struct pci_device_id *id)
 {
+	unsigned i;
+
+	for (i = 0; i < num_except; i++)
+		if (exception_matches(&except[i], dev)) {
+			dev_info(&dev->dev, "skipped by stub\n");
+			return -EPERM;
+		}
+
 	dev_info(&dev->dev, "claimed by stub\n");
 	return 0;
 }
@@ -47,6 +83,33 @@ static int __init pci_stub_init(void)
 	if (rc)
 		return rc;
 
+	/* parse exceptions */
+	p = except_str;
+	while ((id = strsep(&p, ","))) {
+		int fields;
+		unsigned domain, bus, dev, fn;
+
+		if (*id == '\0')
+			continue;
+
+		fields = sscanf(id, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
+		if (fields != 4 || domain > 0xffff || bus > 0xff ||
+		    dev > 0x1f || fn > 0x7) {
+			printk(KERN_WARNING
+			       "pci-stub: invalid exception \"%s\"\n", id);
+			continue;
+		}
+
+		if (num_except < MAX_EXCEPT) {
+			struct except *ex = &except[num_except++];
+
+			ex->domain = domain;
+			ex->devid = PCI_DEVID(bus, PCI_DEVFN(dev, fn));
+		} else
+			printk(KERN_WARNING
+			       "pci-stub: no room for exception \"%s\"\n", id);
+	}
+
 	/* no ids passed actually */
 	if (ids[0] == '\0')
 		return 0;
-- 
2.9.2