[dpdk-dev] [PATCH 18.11] pci/vfio: allow mapping MSI-X BARs if kernel allows it

[Anatoly Burakov]

Currently, DPDK will skip mapping some areas (or even an entire BAR)
if MSI-X happens to be in it but is smaller than page address.

Kernels 4.16+ will allow mapping MSI-X BARs [1], and will report this
as a capability flag. Capability flags themselves are also only
supported since kernel 4.6 [2].

This commit will introduce support for checking VFIO capabilities,
and will use it to check if we are allowed to map BARs with MSI-X
tables in them, along with backwards compatibility for older
kernels, including a workaround for a variable rename in VFIO
region info structure [3].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux.git/commit/?id=a32295c612c57990d17fb0f41e7134394b2f35f6

[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux.git/commit/?id=c84982adb23bcf3b99b79ca33527cd2625fbe279

[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux.git/commit/?id=ff63eb638d63b95e489f976428f1df01391e15e4

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
---
 drivers/bus/pci/linux/pci_vfio.c         | 127 ++++++++++++++++++++---
 lib/librte_eal/common/include/rte_vfio.h |  26 +++++
 2 files changed, 140 insertions(+), 13 deletions(-)

diff --git a/drivers/bus/pci/linux/pci_vfio.c b/drivers/bus/pci/linux/pci_vfio.c
index 686386d6a..e7765ee11 100644
--- a/drivers/bus/pci/linux/pci_vfio.c
+++ b/drivers/bus/pci/linux/pci_vfio.c
@@ -415,6 +415,88 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct mapped_pci_resource *vfio_res,
 	return 0;
 }
 
+/*
+ * region info may contain capability headers, so we need to keep reallocating
+ * the memory until we match allocated memory size with argsz.
+ */
+static int
+pci_vfio_get_region_info(int vfio_dev_fd, struct vfio_region_info **info,
+		int region)
+{
+	struct vfio_region_info *ri;
+	size_t argsz = sizeof(*ri);
+	int ret;
+
+	ri = malloc(sizeof(*ri));
+	if (ri == NULL) {
+		RTE_LOG(ERR, EAL, "Cannot allocate memory for region info\n");
+		return -1;
+	}
+again:
+	memset(ri, 0, argsz);
+	ri->argsz = argsz;
+	ri->index = region;
+
+	ret = ioctl(vfio_dev_fd, VFIO_DEVICE_GET_REGION_INFO, info);
+	if (ret) {
+		free(ri);
+		return ret;
+	}
+	if (ri->argsz != argsz) {
+		argsz = ri->argsz;
+		ri = realloc(ri, argsz);
+
+		if (ri == NULL) {
+			RTE_LOG(ERR, EAL, "Cannot reallocate memory for region info\n");
+			return -1;
+		}
+		goto again;
+	}
+	*info = ri;
+
+	return 0;
+}
+
+static struct vfio_info_cap_header *
+pci_vfio_info_cap(struct vfio_region_info *info, int cap)
+{
+	struct vfio_info_cap_header *h;
+	size_t offset;
+
+	if ((info->flags & RTE_VFIO_INFO_FLAG_CAPS) == 0) {
+		/* VFIO info does not advertise capabilities */
+		return NULL;
+	}
+
+	offset = VFIO_CAP_OFFSET(info);
+	while (offset != 0) {
+		h = RTE_PTR_ADD(info, offset);
+		if (h->id == cap)
+			return h;
+		offset = h->next;
+	}
+	return NULL;
+}
+
+static int
+pci_vfio_msix_is_mappable(int vfio_dev_fd, int msix_region)
+{
+	struct vfio_region_info *info;
+	int ret;
+
+	ret = pci_vfio_get_region_info(vfio_dev_fd, &info, msix_region);
+	if (ret < 0)
+		return -1;
+
+	ret = pci_vfio_info_cap(info, RTE_VFIO_CAP_MSIX_MAPPABLE) != NULL;
+
+	/* cleanup */
+	free(info);
+
+	return ret;
+}
+
+
 static int
 pci_vfio_map_resource_primary(struct rte_pci_device *dev)
 {
@@ -464,56 +546,75 @@ pci_vfio_map_resource_primary(struct rte_pci_device *dev)
 	if (ret < 0) {
 		RTE_LOG(ERR, EAL, "  %s cannot get MSI-X BAR number!\n",
 				pci_addr);
-		goto err_vfio_dev_fd;
+		goto err_vfio_res;
+	}
+	/* if we found our MSI-X BAR region, check if we can mmap it */
+	if (vfio_res->msix_table.bar_index != -1) {
+		int ret = pci_vfio_msix_is_mappable(vfio_dev_fd,
+				vfio_res->msix_table.bar_index);
+		if (ret < 0) {
+			RTE_LOG(ERR, EAL, "Couldn't check if MSI-X BAR is mappable\n");
+			goto err_vfio_res;
+		} else if (ret != 0) {
+			/* we can map it, so we don't care where it is */
+			RTE_LOG(DEBUG, EAL, "VFIO reports MSI-X BAR as mappable\n");
+			vfio_res->msix_table.bar_index = -1;
+		}
 	}
 
 	for (i = 0; i < (int) vfio_res->nb_maps; i++) {
-		struct vfio_region_info reg = { .argsz = sizeof(reg) };
+		struct vfio_region_info *reg;
 		void *bar_addr;
 
-		reg.index = i;
-
-		ret = ioctl(vfio_dev_fd, VFIO_DEVICE_GET_REGION_INFO, &reg);
-		if (ret) {
+		ret = pci_vfio_get_region_info(vfio_dev_fd, &reg, i);
+		if (ret < 0) {
 			RTE_LOG(ERR, EAL, "  %s cannot get device region info "
-					"error %i (%s)\n", pci_addr, errno, strerror(errno));
+				"error %i (%s)\n", pci_addr, errno,
+				strerror(errno));
 			goto err_vfio_res;
 		}
 
 		/* chk for io port region */
 		ret = pci_vfio_is_ioport_bar(vfio_dev_fd, i);
-		if (ret < 0)
+		if (ret < 0) {
+			free(reg);
 			goto err_vfio_res;
-		else if (ret) {
+		} else if (ret) {
 			RTE_LOG(INFO, EAL, "Ignore mapping IO port bar(%d)\n",
 					i);
+			free(reg);
 			continue;
 		}
 
 		/* skip non-mmapable BARs */
-		if ((reg.flags & VFIO_REGION_INFO_FLAG_MMAP) == 0)
+		if ((reg->flags & VFIO_REGION_INFO_FLAG_MMAP) == 0) {
+			free(reg);
 			continue;
+		}
 
 		/* try mapping somewhere close to the end of hugepages */
 		if (pci_map_addr == NULL)
 			pci_map_addr = pci_find_max_end_va();
 
 		bar_addr = pci_map_addr;
-		pci_map_addr = RTE_PTR_ADD(bar_addr, (size_t) reg.size);
+		pci_map_addr = RTE_PTR_ADD(bar_addr, (size_t) reg->size);
 
 		maps[i].addr = bar_addr;
-		maps[i].offset = reg.offset;
-		maps[i].size = reg.size;
+		maps[i].offset = reg->offset;
+		maps[i].size = reg->size;
 		maps[i].path = NULL; /* vfio doesn't have per-resource paths */
 
 		ret = pci_vfio_mmap_bar(vfio_dev_fd, vfio_res, i, 0);
 		if (ret < 0) {
 			RTE_LOG(ERR, EAL, "  %s mapping BAR%i failed: %s\n",
 					pci_addr, i, strerror(errno));
+			free(reg);
 			goto err_vfio_res;
 		}
 
 		dev->mem_resource[i].addr = maps[i].addr;
+
+		free(reg);
 	}
 
 	if (pci_rte_vfio_setup_device(dev, vfio_dev_fd) < 0) {
diff --git a/lib/librte_eal/common/include/rte_vfio.h b/lib/librte_eal/common/include/rte_vfio.h
index 5ca13fcce..f6617e004 100644
--- a/lib/librte_eal/common/include/rte_vfio.h
+++ b/lib/librte_eal/common/include/rte_vfio.h
@@ -14,6 +14,8 @@
 extern "C" {
 #endif
 
+#include <stdint.h>
+
 /*
  * determine if VFIO is present on the system
  */
@@ -44,6 +46,30 @@ extern "C" {
 #define RTE_VFIO_NOIOMMU 8
 #endif
 
+/*
+ * capabilities are only supported on kernel 4.6+. there were also some API
+ * changes as well, so add a macro to get cap offset.
+ */
+#ifdef VFIO_REGION_INFO_FLAG_CAPS
+#define RTE_VFIO_INFO_FLAG_CAPS VFIO_REGION_INFO_FLAG_CAPS
+#define VFIO_CAP_OFFSET(x) (x->cap_offset)
+#else
+#define RTE_VFIO_INFO_FLAG_CAPS (1 << 3)
+#define VFIO_CAP_OFFSET(x) (x->resv)
+struct vfio_info_cap_header {
+	uint16_t id;
+	uint16_t version;
+	uint32_t next;
+};
+#endif
+
+/* kernels 4.16+ can map BAR containing MSI-X table */
+#ifdef VFIO_REGION_INFO_CAP_MSIX_MAPPABLE
+#define RTE_VFIO_CAP_MSIX_MAPPABLE VFIO_REGION_INFO_CAP_MSIX_MAPPABLE
+#else
+#define RTE_VFIO_CAP_MSIX_MAPPABLE 3
+#endif
+
 #else /* not VFIO_PRESENT */
 
 /* we don't need an actual definition, only pointer is used */
-- 
2.17.1