Re: [PATCH 0/3] virtio-mmio: handle BE guests on LE hosts

Rusty Russell
2013-10-14T08:57:36Z

Marc Zyngier <marc.zyngier@arm.com> writes:
> This small patch series adds just enough kernel infrastructure and
> fixes to allow a BE guest to use virtio-mmio on a LE host, provided
> that the host actually supports such madness.
>
> This has been tested on arm64, with some fixes to KVM and a set of
> changes to kvmtool, both which I am posting separately.

OK, so I already have a patch which supports config space accessors.
I've posted the series below, and since you want it, I'll put it in
virtio-next after more testing and rebasing...

But we won't be using feature bits for endianness, since we're defining
endian in the 1.0 spec (whether LE-everywhere or LE-for-mmio-and-PCI is
still debated). Since we need to guess for backwards compat anyway,
let's keep doing this until v1.0?

(Yeah, I made this mess with "native endian". I promise I have learnt
my lesson).

Thanks,
Rusty.

Subject: virtio_config: introduce size-based accessors.

This lets the us do endian conversion if necessary, and insulates the
drivers from that change.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 29b9104..e62acdd 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -162,5 +135,139 @@ int virtqueue_set_affinity(struct virtqueue *vq, int cpu)
return 0;
}

+/* Config space accessors. */
+#define virtio_cread(vdev, structname, member, ptr) \
+ do { \
+ /* Must match the member's type, and be integer */ \
+ if (!typecheck(typeof((((structname*)0)->member)), *(ptr))) \
+ (*ptr) = 1; \
+ \
+ switch (sizeof(*ptr)) { \
+ case 1: \
+ *(ptr) = virtio_cread8(vdev, \
+ offsetof(structname, member)); \
+ break; \
+ case 2: \
+ *(ptr) = virtio_cread16(vdev, \
+ offsetof(structname, member)); \
+ break; \
+ case 4: \
+ *(ptr) = virtio_cread32(vdev, \
+ offsetof(structname, member)); \
+ break; \
+ case 8: \
+ *(ptr) = virtio_cread64(vdev, \
+ offsetof(structname, member)); \
+ break; \
+ default: \
+ BUG(); \
+ } \
+ } while(0)
+
+/* Config space accessors. */
+#define virtio_cwrite(vdev, structname, member, ptr) \
+ do { \
+ /* Must match the member's type, and be integer */ \
+ if (!typecheck(typeof((((structname*)0)->member)), *(ptr))) \
+ BUG_ON((*ptr) == 1); \
+ \
+ switch (sizeof(*ptr)) { \
+ case 1: \
+ virtio_cwrite8(vdev, \
+ offsetof(structname, member), \
+ *(ptr)); \
+ break; \
+ case 2: \
+ virtio_cwrite16(vdev, \
+ offsetof(structname, member), \
+ *(ptr)); \
+ break; \
+ case 4: \
+ virtio_cwrite32(vdev, \
+ offsetof(structname, member), \
+ *(ptr)); \
+ break; \
+ case 8: \
+ virtio_cwrite64(vdev, \
+ offsetof(structname, member), \
+ *(ptr)); \
+ break; \
+ default: \
+ BUG(); \
+ } \
+ } while(0)
+
+static inline u8 virtio_cread8(struct virtio_device *vdev, unsigned int offset)
+{
+ u8 ret;
+ vdev->config->get(vdev, offset, &ret, sizeof(ret));
+ return ret;
+}
+
+static inline void virtio_cread_bytes(struct virtio_device *vdev,
+ unsigned int offset,
+ void *buf, size_t len)
+{
+ vdev->config->get(vdev, offset, buf, len);
+}
+
+static inline void virtio_cwrite8(struct virtio_device *vdev,
+ unsigned int offset, u8 val)
+{
+ vdev->config->set(vdev, offset, &val, sizeof(val));
+}
+
+static inline u16 virtio_cread16(struct virtio_device *vdev,
+ unsigned int offset)
+{
+ u16 ret;
+ vdev->config->get(vdev, offset, &ret, sizeof(ret));
+ return ret;
+}
+
+static inline void virtio_cwrite16(struct virtio_device *vdev,
+ unsigned int offset, u16 val)
+{
+ vdev->config->set(vdev, offset, &val, sizeof(val));
+}
+
+static inline u32 virtio_cread32(struct virtio_device *vdev,
+ unsigned int offset)
+{
+ u32 ret;
+ vdev->config->get(vdev, offset, &ret, sizeof(ret));
+ return ret;
+}
+
+static inline void virtio_cwrite32(struct virtio_device *vdev,
+ unsigned int offset, u32 val)
+{
+ vdev->config->set(vdev, offset, &val, sizeof(val));
+}
+
+static inline u64 virtio_cread64(struct virtio_device *vdev,
+ unsigned int offset)
+{
+ u64 ret;
+ vdev->config->get(vdev, offset, &ret, sizeof(ret));
+ return ret;
+}
+
+static inline void virtio_cwrite64(struct virtio_device *vdev,
+ unsigned int offset, u64 val)
+{
+ vdev->config->set(vdev, offset, &val, sizeof(val));
+}
+
+/* Conditional config space accessors. */
+#define virtio_cread_feature(vdev, fbit, structname, member, ptr) \
+ ({ \
+ int _r = 0; \
+ if (!virtio_has_feature(vdev, fbit)) \
+ _r = -ENOENT; \
+ else \
+ virtio_cread((vdev), structname, member, ptr); \
+ _r; \
+ })

#endif /* _LINUX_VIRTIO_CONFIG_H */

Subject: virtio: use size-based config accessors.

This lets the transport do endian conversion if necessary, and insulates
the drivers from the difference.

Most drivers can use the simple helpers virtio_cread() and virtio_cwrite().

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 6472395..1b1bbd3 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -456,18 +456,15 @@ static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
{
struct virtio_blk *vblk = bd->bd_disk->private_data;
- struct virtio_blk_geometry vgeo;
- int err;

/* see if the host passed in geometry config */
- err = virtio_config_val(vblk->vdev, VIRTIO_BLK_F_GEOMETRY,
- offsetof(struct virtio_blk_config, geometry),
- &vgeo);
-
- if (!err) {
- geo->heads = vgeo.heads;
- geo->sectors = vgeo.sectors;
- geo->cylinders = vgeo.cylinders;
+ if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) {
+ virtio_cread(vblk->vdev, struct virtio_blk_config,
+ geometry.cylinders, &geo->cylinders);
+ virtio_cread(vblk->vdev, struct virtio_blk_config,
+ geometry.heads, &geo->heads);
+ virtio_cread(vblk->vdev, struct virtio_blk_config,
+ geometry.sectors, &geo->sectors);
} else {
/* some standard values, similar to sd */
geo->heads = 1 << 6;
@@ -529,8 +526,7 @@ static void virtblk_config_changed_work(struct work_struct *work)
goto done;

/* Host must always specify the capacity. */
- vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
- &capacity, sizeof(capacity));
+ virtio_cread(vdev, struct virtio_blk_config, capacity, &capacity);

/* If capacity is too big, truncate with warning. */
if ((sector_t)capacity != capacity) {
@@ -608,9 +604,9 @@ static int virtblk_get_cache_mode(struct virtio_device *vdev)
u8 writeback;
int err;

- err = virtio_config_val(vdev, VIRTIO_BLK_F_CONFIG_WCE,
- offsetof(struct virtio_blk_config, wce),
- &writeback);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_CONFIG_WCE,
+ struct virtio_blk_config, wce,
+ &writeback);
if (err)
writeback = virtio_has_feature(vdev, VIRTIO_BLK_F_WCE);

@@ -642,7 +638,6 @@ virtblk_cache_type_store(struct device *dev, struct device_attribute *attr,
struct virtio_blk *vblk = disk->private_data;
struct virtio_device *vdev = vblk->vdev;
int i;
- u8 writeback;

BUG_ON(!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_CONFIG_WCE));
for (i = ARRAY_SIZE(virtblk_cache_types); --i >= 0; )
@@ -652,11 +647,7 @@ virtblk_cache_type_store(struct device *dev, struct device_attribute *attr,
if (i < 0)
return -EINVAL;

- writeback = i;
- vdev->config->set(vdev,
- offsetof(struct virtio_blk_config, wce),
- &writeback, sizeof(writeback));
-
+ virtio_cwrite8(vdev, offsetof(struct virtio_blk_config, wce), i);
virtblk_update_cache_mode(vdev);
return count;
}
@@ -699,9 +690,9 @@ static int virtblk_probe(struct virtio_device *vdev)
index = err;

/* We need to know how many segments before we allocate. */
- err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
- offsetof(struct virtio_blk_config, seg_max),
- &sg_elems);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SEG_MAX,
+ struct virtio_blk_config, seg_max,
+ &sg_elems);

/* We need at least one SG element, whatever they say. */
if (err || !sg_elems)
@@ -772,8 +763,7 @@ static int virtblk_probe(struct virtio_device *vdev)
set_disk_ro(vblk->disk, 1);

/* Host must always specify the capacity. */
- vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity),
- &cap, sizeof(cap));
+ virtio_cread(vdev, struct virtio_blk_config, capacity, &cap);

/* If capacity is too big, truncate with warning. */
if ((sector_t)cap != cap) {
@@ -794,46 +784,45 @@ static int virtblk_probe(struct virtio_device *vdev)

/* Host can optionally specify maximum segment size and number of
* segments. */
- err = virtio_config_val(vdev, VIRTIO_BLK_F_SIZE_MAX,
- offsetof(struct virtio_blk_config, size_max),
- &v);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
+ struct virtio_blk_config, size_max, &v);
if (!err)
blk_queue_max_segment_size(q, v);
else
blk_queue_max_segment_size(q, -1U);

/* Host can optionally specify the block size of the device */
- err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
- offsetof(struct virtio_blk_config, blk_size),
- &blk_size);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
+ struct virtio_blk_config, blk_size,
+ &blk_size);
if (!err)
blk_queue_logical_block_size(q, blk_size);
else
blk_size = queue_logical_block_size(q);

/* Use topology information if available */
- err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
- offsetof(struct virtio_blk_config, physical_block_exp),
- &physical_block_exp);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ struct virtio_blk_config, physical_block_exp,
+ &physical_block_exp);
if (!err && physical_block_exp)
blk_queue_physical_block_size(q,
blk_size * (1 << physical_block_exp));

- err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
- offsetof(struct virtio_blk_config, alignment_offset),
- &alignment_offset);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ struct virtio_blk_config, alignment_offset,
+ &alignment_offset);
if (!err && alignment_offset)
blk_queue_alignment_offset(q, blk_size * alignment_offset);

- err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
- offsetof(struct virtio_blk_config, min_io_size),
- &min_io_size);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ struct virtio_blk_config, min_io_size,
+ &min_io_size);
if (!err && min_io_size)
blk_queue_io_min(q, blk_size * min_io_size);

- err = virtio_config_val(vdev, VIRTIO_BLK_F_TOPOLOGY,
- offsetof(struct virtio_blk_config, opt_io_size),
- &opt_io_size);
+ err = virtio_cread_feature(vdev, VIRTIO_BLK_F_TOPOLOGY,
+ struct virtio_blk_config, opt_io_size,
+ &opt_io_size);
if (!err && opt_io_size)
blk_queue_io_opt(q, blk_size * opt_io_size);

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index e6ba6b7..1735c38 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1800,12 +1800,8 @@ static void config_intr(struct virtio_device *vdev)
struct port *port;
u16 rows, cols;

- vdev->config->get(vdev,
- offsetof(struct virtio_console_config, cols),
- &cols, sizeof(u16));
- vdev->config->get(vdev,
- offsetof(struct virtio_console_config, rows),
- &rows, sizeof(u16));
+ virtio_cread(vdev, struct virtio_console_config, cols, &cols);
+ virtio_cread(vdev, struct virtio_console_config, rows, &rows);

port = find_port_by_id(portdev, 0);
set_console_size(port, rows, cols);
@@ -1977,10 +1973,9 @@ static int virtcons_probe(struct virtio_device *vdev)

/* Don't test MULTIPORT at all if we're rproc: not a valid feature! */
if (!is_rproc_serial(vdev) &&
- virtio_config_val(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
- offsetof(struct virtio_console_config,
- max_nr_ports),
- &portdev->config.max_nr_ports) == 0) {
+ virtio_cread_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
+ struct virtio_console_config, max_nr_ports,
+ &portdev->config.max_nr_ports) == 0) {
multiport = true;
}

diff --git a/drivers/net/caif/caif_virtio.c b/drivers/net/caif/caif_virtio.c
index 8308dee..ef602e3 100644
--- a/drivers/net/caif/caif_virtio.c
+++ b/drivers/net/caif/caif_virtio.c
@@ -682,18 +682,19 @@ static int cfv_probe(struct virtio_device *vdev)
goto err;

/* Get the CAIF configuration from virtio config space, if available */
-#define GET_VIRTIO_CONFIG_OPS(_v, _var, _f) \
- ((_v)->config->get(_v, offsetof(struct virtio_caif_transf_config, _f), \
- &_var, \
- FIELD_SIZEOF(struct virtio_caif_transf_config, _f)))
-
if (vdev->config->get) {
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->tx_hr, headroom);
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->rx_hr, headroom);
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->tx_tr, tailroom);
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->rx_tr, tailroom);
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->mtu, mtu);
- GET_VIRTIO_CONFIG_OPS(vdev, cfv->mru, mtu);
+ virtio_cread(vdev, struct virtio_caif_transf_config, headroom,
+ &cfv->tx_hr);
+ virtio_cread(vdev, struct virtio_caif_transf_config, headroom,
+ &cfv->rx_hr);
+ virtio_cread(vdev, struct virtio_caif_transf_config, tailroom,
+ &cfv->tx_tr);
+ virtio_cread(vdev, struct virtio_caif_transf_config, tailroom,
+ &cfv->rx_tr);
+ virtio_cread(vdev, struct virtio_caif_transf_config, mtu,
+ &cfv->mtu);
+ virtio_cread(vdev, struct virtio_caif_transf_config, mtu,
+ &cfv->mru);
} else {
cfv->tx_hr = CFV_DEF_HEADROOM;
cfv->rx_hr = CFV_DEF_HEADROOM;
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index be70487..61c1592 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -829,8 +829,13 @@ static int virtnet_set_mac_address(struct net_device *dev, void *p)
return -EINVAL;
}
} else if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC)) {
- vdev->config->set(vdev, offsetof(struct virtio_net_config, mac),
- addr->sa_data, dev->addr_len);
+ unsigned int i;
+
+ /* Naturally, this has an atomicity problem. */
+ for (i = 0; i < dev->addr_len; i++)
+ virtio_cwrite8(vdev,
+ offsetof(struct virtio_net_config, mac) +
+ i, addr->sa_data[i]);
}

eth_commit_mac_addr_change(dev, p);
@@ -1239,9 +1244,8 @@ static void virtnet_config_changed_work(struct work_struct *work)
if (!vi->config_enable)
goto done;

- if (virtio_config_val(vi->vdev, VIRTIO_NET_F_STATUS,
- offsetof(struct virtio_net_config, status),
- &v) < 0)
+ if (virtio_cread_feature(vi->vdev, VIRTIO_NET_F_STATUS,
+ struct virtio_net_config, status, &v) < 0)
goto done;

if (v & VIRTIO_NET_S_ANNOUNCE) {
@@ -1463,9 +1467,9 @@ static int virtnet_probe(struct virtio_device *vdev)
u16 max_queue_pairs;

/* Find if host supports multiqueue virtio_net device */
- err = virtio_config_val(vdev, VIRTIO_NET_F_MQ,
- offsetof(struct virtio_net_config,
- max_virtqueue_pairs), &max_queue_pairs);
+ err = virtio_cread_feature(vdev, VIRTIO_NET_F_MQ,
+ struct virtio_net_config,
+ max_virtqueue_pairs, &max_queue_pairs);

/* We need at least 2 queue's */
if (err || max_queue_pairs < VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN ||
@@ -1513,9 +1517,11 @@ static int virtnet_probe(struct virtio_device *vdev)
}

/* Configuration may specify what MAC to use. Otherwise random. */
- if (virtio_config_val_len(vdev, VIRTIO_NET_F_MAC,
- offsetof(struct virtio_net_config, mac),
- dev->dev_addr, dev->addr_len) < 0)
+ if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
+ virtio_cread_bytes(vdev,
+ offsetof(struct virtio_net_config, mac),
+ dev->dev_addr, dev->addr_len);
+ else
eth_hw_addr_random(dev);

/* Set up our device-specific information */
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index f679b8c..a20418f 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -547,19 +547,15 @@ static struct scsi_host_template virtscsi_host_template = {
#define virtscsi_config_get(vdev, fld) \
({ \
typeof(((struct virtio_scsi_config *)0)->fld) __val; \
- vdev->config->get(vdev, \
- offsetof(struct virtio_scsi_config, fld), \
- &__val, sizeof(__val)); \
+ virtio_cread(vdev, struct virtio_scsi_config, fld, &__val); \
__val; \
})

#define virtscsi_config_set(vdev, fld, val) \
- (void)({ \
+ do { \
typeof(((struct virtio_scsi_config *)0)->fld) __val = (val); \
- vdev->config->set(vdev, \
- offsetof(struct virtio_scsi_config, fld), \
- &__val, sizeof(__val)); \
- })
+ virtio_cwrite(vdev, struct virtio_scsi_config, fld, &__val); \
+ } while(0)

static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
struct virtqueue *vq)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 8dab163..bbab952 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -273,9 +273,8 @@ static inline s64 towards_target(struct virtio_balloon *vb)
__le32 v;
s64 target;

- vb->vdev->config->get(vb->vdev,
- offsetof(struct virtio_balloon_config, num_pages),
- &v, sizeof(v));
+ virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages, &v);
+
target = le32_to_cpu(v);
return target - vb->num_pages;
}
@@ -284,9 +283,8 @@ static void update_balloon_size(struct virtio_balloon *vb)
{
__le32 actual = cpu_to_le32(vb->num_pages);

- vb->vdev->config->set(vb->vdev,
- offsetof(struct virtio_balloon_config, actual),
- &actual, sizeof(actual));
+ virtio_cwrite(vb->vdev, struct virtio_balloon_config, num_pages,
+ &actual);
}

static int balloon(void *_vballoon)
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index de2e950..d843d5d 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -514,9 +514,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)

chan->inuse = false;
if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
- vdev->config->get(vdev,
- offsetof(struct virtio_9p_config, tag_len),
- &tag_len, sizeof(tag_len));
+ virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
} else {
err = -EINVAL;
goto out_free_vq;
@@ -526,8 +524,9 @@ static int p9_virtio_probe(struct virtio_device *vdev)
err = -ENOMEM;
goto out_free_vq;
}
- vdev->config->get(vdev, offsetof(struct virtio_9p_config, tag),
- tag, tag_len);
+
+ virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
+ tag, tag_len);
chan->tag = tag;
chan->tag_len = tag_len;
err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);

Subject: virtio_config: remove virtio_config_val

The virtio_cread() functions should now be used.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 29b9104..e62acdd 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -96,33 +96,6 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev,
return test_bit(fbit, vdev->features);
}

-/**
- * virtio_config_val - look for a feature and get a virtio config entry.
- * @vdev: the virtio device
- * @fbit: the feature bit
- * @offset: the type to search for.
- * @v: a pointer to the value to fill in.
- *
- * The return value is -ENOENT if the feature doesn't exist. Otherwise
- * the config value is copied into whatever is pointed to by v. */
-#define virtio_config_val(vdev, fbit, offset, v) \
- virtio_config_buf((vdev), (fbit), (offset), (v), sizeof(*v))
-
-#define virtio_config_val_len(vdev, fbit, offset, v, len) \
- virtio_config_buf((vdev), (fbit), (offset), (v), (len))
-
-static inline int virtio_config_buf(struct virtio_device *vdev,
- unsigned int fbit,
- unsigned int offset,
- void *buf, unsigned len)
-{
- if (!virtio_has_feature(vdev, fbit))
- return -ENOENT;
-
- vdev->config->get(vdev, offset, buf, len);
- return 0;
-}
-
static inline
struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
vq_callback_t *c, const char *n)