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Subject[PATCH 15/52] fuse: map virtio_fs DAX window BAR
Date
From: Stefan Hajnoczi <stefanha@redhat.com>

Experimental QEMU code introduces an MMIO BAR for mapping portions of
files in the virtio-fs device. Map this BAR so that FUSE DAX can access
file contents from the host page cache.

The DAX window is accessed by the fs/dax.c infrastructure and must have
struct pages (at least on x86). Use devm_memremap_pages() to map the
DAX window PCI BAR and allocate struct page.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
fs/fuse/virtio_fs.c | 166 ++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 143 insertions(+), 23 deletions(-)

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index ba615ec2603e..87b7e42a6763 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -6,12 +6,18 @@

#include <linux/fs.h>
#include <linux/dax.h>
+#include <linux/pci.h>
#include <linux/pfn_t.h>
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_fs.h>
#include "fuse_i.h"

+enum {
+ /* PCI BAR number of the virtio-fs DAX window */
+ VIRTIO_FS_WINDOW_BAR = 2,
+};
+
/* List of virtio-fs device instances and a lock for the list */
static DEFINE_MUTEX(virtio_fs_mutex);
static LIST_HEAD(virtio_fs_instances);
@@ -24,6 +30,18 @@ struct virtio_fs_vq {
char name[24];
} ____cacheline_aligned_in_smp;

+/* State needed for devm_memremap_pages(). This API is called on the
+ * underlying pci_dev instead of struct virtio_fs (layering violation). Since
+ * the memremap release function only gets called when the pci_dev is released,
+ * keep the associated state separate from struct virtio_fs (it has a different
+ * lifecycle from pci_dev).
+ */
+struct virtio_fs_memremap_info {
+ struct dev_pagemap pgmap;
+ struct percpu_ref ref;
+ struct completion completion;
+};
+
/* A virtio-fs device instance */
struct virtio_fs {
struct list_head list; /* on virtio_fs_instances */
@@ -36,6 +54,7 @@ struct virtio_fs {
/* DAX memory window where file contents are mapped */
void *window_kaddr;
phys_addr_t window_phys_addr;
+ size_t window_len;
};

static inline struct virtio_fs_vq *vq_to_fsvq(struct virtqueue *vq)
@@ -395,6 +414,127 @@ static const struct dax_operations virtio_fs_dax_ops = {
.copy_to_iter = virtio_fs_copy_to_iter,
};

+static void virtio_fs_percpu_release(struct percpu_ref *ref)
+{
+ struct virtio_fs_memremap_info *mi =
+ container_of(ref, struct virtio_fs_memremap_info, ref);
+
+ complete(&mi->completion);
+}
+
+static void virtio_fs_percpu_exit(void *data)
+{
+ struct virtio_fs_memremap_info *mi = data;
+
+ wait_for_completion(&mi->completion);
+ percpu_ref_exit(&mi->ref);
+}
+
+static void virtio_fs_percpu_kill(void *data)
+{
+ percpu_ref_kill(data);
+}
+
+static void virtio_fs_cleanup_dax(void *data)
+{
+ struct virtio_fs *fs = data;
+
+ kill_dax(fs->dax_dev);
+ put_dax(fs->dax_dev);
+}
+
+static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs)
+{
+ struct virtio_fs_memremap_info *mi;
+ struct dev_pagemap *pgmap;
+ struct pci_dev *pci_dev;
+ phys_addr_t phys_addr;
+ size_t len;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_DAX_DRIVER))
+ return 0;
+
+ /* HACK implement VIRTIO shared memory regions instead of
+ * directly accessing the PCI BAR from a virtio device driver.
+ */
+ pci_dev = container_of(vdev->dev.parent, struct pci_dev, dev);
+
+ /* TODO Is this safe - the virtio_pci_* driver doesn't use managed
+ * device APIs? */
+ ret = pcim_enable_device(pci_dev);
+ if (ret < 0)
+ return ret;
+
+ /* TODO handle case where device doesn't expose BAR? */
+ ret = pci_request_region(pci_dev, VIRTIO_FS_WINDOW_BAR,
+ "virtio-fs-window");
+ if (ret < 0) {
+ dev_err(&vdev->dev, "%s: failed to request window BAR\n",
+ __func__);
+ return ret;
+ }
+
+ phys_addr = pci_resource_start(pci_dev, VIRTIO_FS_WINDOW_BAR);
+ len = pci_resource_len(pci_dev, VIRTIO_FS_WINDOW_BAR);
+
+ mi = devm_kzalloc(&pci_dev->dev, sizeof(*mi), GFP_KERNEL);
+ if (!mi)
+ return -ENOMEM;
+
+ init_completion(&mi->completion);
+ ret = percpu_ref_init(&mi->ref, virtio_fs_percpu_release, 0,
+ GFP_KERNEL);
+ if (ret < 0) {
+ dev_err(&vdev->dev, "%s: percpu_ref_init failed (%d)\n",
+ __func__, ret);
+ return ret;
+ }
+
+ ret = devm_add_action(&pci_dev->dev, virtio_fs_percpu_exit, mi);
+ if (ret < 0) {
+ percpu_ref_exit(&mi->ref);
+ return ret;
+ }
+
+ pgmap = &mi->pgmap;
+ pgmap->altmap_valid = false;
+ pgmap->ref = &mi->ref;
+ pgmap->type = MEMORY_DEVICE_FS_DAX;
+
+ /* Ideally we would directly use the PCI BAR resource but
+ * devm_memremap_pages() wants its own copy in pgmap. So
+ * initialize a struct resource from scratch (only the start
+ * and end fields will be used).
+ */
+ pgmap->res = (struct resource){
+ .name = "virtio-fs dax window",
+ .start = phys_addr,
+ .end = phys_addr + len,
+ };
+
+ fs->window_kaddr = devm_memremap_pages(&pci_dev->dev, pgmap);
+ if (IS_ERR(fs->window_kaddr))
+ return PTR_ERR(fs->window_kaddr);
+
+ ret = devm_add_action_or_reset(&pci_dev->dev, virtio_fs_percpu_kill,
+ &mi->ref);
+ if (ret < 0)
+ return ret;
+
+ fs->window_phys_addr = phys_addr;
+ fs->window_len = len;
+
+ dev_dbg(&vdev->dev, "%s: window kaddr 0x%px phys_addr 0x%llx len %zu\n",
+ __func__, fs->window_kaddr, phys_addr, len);
+
+ fs->dax_dev = alloc_dax(fs, NULL, &virtio_fs_dax_ops);
+ if (!fs->dax_dev)
+ return -ENOMEM;
+
+ return devm_add_action_or_reset(&vdev->dev, virtio_fs_cleanup_dax, fs);
+}
+
static int virtio_fs_probe(struct virtio_device *vdev)
{
struct virtio_fs *fs;
@@ -416,16 +556,9 @@ static int virtio_fs_probe(struct virtio_device *vdev)
/* TODO vq affinity */
/* TODO populate notifications vq */

- if (IS_ENABLED(CONFIG_DAX_DRIVER)) {
- /* TODO map window */
- fs->window_kaddr = NULL;
- fs->window_phys_addr = 0;
-
- fs->dax_dev = alloc_dax(fs, NULL, &virtio_fs_dax_ops);
- if (!fs->dax_dev)
- goto out_vqs; /* TODO handle case where device doesn't expose
- BAR */
- }
+ ret = virtio_fs_setup_dax(vdev, fs);
+ if (ret < 0)
+ goto out_vqs;

/* Bring the device online in case the filesystem is mounted and
* requests need to be sent before we return.
@@ -441,13 +574,6 @@ static int virtio_fs_probe(struct virtio_device *vdev)
out_vqs:
vdev->config->reset(vdev);
virtio_fs_cleanup_vqs(vdev, fs);
-
- if (fs->dax_dev) {
- kill_dax(fs->dax_dev);
- put_dax(fs->dax_dev);
- fs->dax_dev = NULL;
- }
-
out:
vdev->priv = NULL;
return ret;
@@ -466,12 +592,6 @@ static void virtio_fs_remove(struct virtio_device *vdev)
list_del(&fs->list);
mutex_unlock(&virtio_fs_mutex);

- if (fs->dax_dev) {
- kill_dax(fs->dax_dev);
- put_dax(fs->dax_dev);
- fs->dax_dev = NULL;
- }
-
vdev->priv = NULL;
}

--
2.13.6
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