[PATCH v3 2/2] vhost: switch to arrays of feature bits

Michael S. Tsirkin
2025-11-16T07:36:32Z

The current interface where caller has to know in which 64 bit chunk
each bit is, is inelegant and fragile.
Let's simply use arrays of bits.
By using unroll macros text size grows only slightly.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/net.c | 34 +++++++++++++++++++---------------
drivers/vhost/scsi.c | 9 ++++++---
drivers/vhost/test.c | 10 ++++++++--
drivers/vhost/vhost.h | 42 ++++++++++++++++++++++++++++++++++--------
drivers/vhost/vsock.c | 10 ++++++----
5 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d057ea55f5ad..00d00034a97e 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -69,15 +69,15 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"

#define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)

-static const u64 vhost_net_features[VIRTIO_FEATURES_U64S] = {
- VHOST_FEATURES |
- (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
- (1ULL << VIRTIO_NET_F_MRG_RXBUF) |
- (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
- (1ULL << VIRTIO_F_RING_RESET) |
- (1ULL << VIRTIO_F_IN_ORDER),
- VIRTIO_BIT(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
- VIRTIO_BIT(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO),
+static const int vhost_net_features[] = {
+ VHOST_FEATURES,
+ VHOST_NET_F_VIRTIO_NET_HDR,
+ VIRTIO_NET_F_MRG_RXBUF,
+ VIRTIO_F_ACCESS_PLATFORM,
+ VIRTIO_F_RING_RESET,
+ VIRTIO_F_IN_ORDER,
+ VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO,
+ VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO
};

enum {
@@ -1734,14 +1734,14 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
return -EFAULT;
return vhost_net_set_backend(n, backend.index, backend.fd);
case VHOST_GET_FEATURES:
- features = vhost_net_features[0];
+ features = VHOST_FEATURES_U64(vhost_net_features, 0);
if (copy_to_user(featurep, &features, sizeof features))
return -EFAULT;
return 0;
case VHOST_SET_FEATURES:
if (copy_from_user(&features, featurep, sizeof features))
return -EFAULT;
- if (features & ~vhost_net_features[0])
+ if (features & ~VHOST_FEATURES_U64(vhost_net_features, 0))
return -EOPNOTSUPP;

virtio_features_from_u64(all_features, features);
@@ -1753,9 +1753,13 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
/* Copy the net features, up to the user-provided buffer size */
argp += sizeof(u64);
copied = min(count, (u64)VIRTIO_FEATURES_U64S);
- if (copy_to_user(argp, vhost_net_features,
- copied * sizeof(u64)))
- return -EFAULT;
+
+ {
+ const DEFINE_VHOST_FEATURES_ARRAY(features, vhost_net_features);
+
+ if (copy_to_user(argp, features, copied * sizeof(u64)))
+ return -EFAULT;
+ }

/* Zero the trailing space provided by user-space, if any */
if (clear_user(argp, size_mul(count - copied, sizeof(u64))))
@@ -1784,7 +1788,7 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
}

for (i = 0; i < VIRTIO_FEATURES_U64S; i++)
- if (all_features[i] & ~vhost_net_features[i])
+ if (all_features[i] & ~VHOST_FEATURES_U64(vhost_net_features, i))
return -EOPNOTSUPP;

return vhost_net_set_features(n, all_features);
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 98e4f68f4e3c..04fcbe7efd77 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -197,11 +197,14 @@ enum {
};

/* Note: can't set VIRTIO_F_VERSION_1 yet, since that implies ANY_LAYOUT. */
-enum {
- VHOST_SCSI_FEATURES = VHOST_FEATURES | (1ULL << VIRTIO_SCSI_F_HOTPLUG) |
- (1ULL << VIRTIO_SCSI_F_T10_PI)
+static const int vhost_scsi_features[] = {
+ VHOST_FEATURES,
+ VIRTIO_SCSI_F_HOTPLUG,
+ VIRTIO_SCSI_F_T10_PI
};

+#define VHOST_SCSI_FEATURES VHOST_FEATURES_U64(vhost_scsi_features, 0)
+
#define VHOST_SCSI_MAX_TARGET 256
#define VHOST_SCSI_MAX_IO_VQ 1024
#define VHOST_SCSI_MAX_EVENT 128
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 42c955a5b211..af727fccfe40 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -308,6 +308,12 @@ static long vhost_test_set_backend(struct vhost_test *n, unsigned index, int fd)
return r;
}

+static const int vhost_test_features[] = {
+ VHOST_FEATURES
+};
+
+#define VHOST_TEST_FEATURES VHOST_FEATURES_U64(vhost_test_features, 0)
+
static long vhost_test_ioctl(struct file *f, unsigned int ioctl,
unsigned long arg)
{
@@ -328,14 +334,14 @@ static long vhost_test_ioctl(struct file *f, unsigned int ioctl,
return -EFAULT;
return vhost_test_set_backend(n, backend.index, backend.fd);
case VHOST_GET_FEATURES:
- features = VHOST_FEATURES;
+ features = VHOST_TEST_FEATURES;
if (copy_to_user(featurep, &features, sizeof features))
return -EFAULT;
return 0;
case VHOST_SET_FEATURES:
if (copy_from_user(&features, featurep, sizeof features))
return -EFAULT;
- if (features & ~VHOST_FEATURES)
+ if (features & ~VHOST_TEST_FEATURES)
return -EOPNOTSUPP;
return vhost_test_set_features(n, features);
case VHOST_RESET_OWNER:
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 621a6d9a8791..d8f1af9a0ff1 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -14,6 +14,7 @@
#include <linux/atomic.h>
#include <linux/vhost_iotlb.h>
#include <linux/irqbypass.h>
+#include <linux/unroll.h>

struct vhost_work;
struct vhost_task;
@@ -279,14 +280,39 @@ void vhost_iotlb_map_free(struct vhost_iotlb *iotlb,
eventfd_signal((vq)->error_ctx);\
} while (0)

-enum {
- VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
- (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
- (1ULL << VIRTIO_RING_F_EVENT_IDX) |
- (1ULL << VHOST_F_LOG_ALL) |
- (1ULL << VIRTIO_F_ANY_LAYOUT) |
- (1ULL << VIRTIO_F_VERSION_1)
-};
+#define VHOST_FEATURES \
+ VIRTIO_F_NOTIFY_ON_EMPTY, \
+ VIRTIO_RING_F_INDIRECT_DESC, \
+ VIRTIO_RING_F_EVENT_IDX, \
+ VHOST_F_LOG_ALL, \
+ VIRTIO_F_ANY_LAYOUT, \
+ VIRTIO_F_VERSION_1
+
+static inline u64 vhost_features_u64(const int *features, int size, int idx)
+{
+ unsigned long res = 0;
+
+ unrolled_count(VIRTIO_FEATURES_BITS)
+ for (int i = 0; i < size; ++i) {
+ int bit = features[i];
+
+ if (virtio_features_chk_bit(bit) && VIRTIO_U64(bit) == idx)
+ res |= VIRTIO_BIT(bit);
+ }
+ return res;
+}
+
+#define VHOST_FEATURES_U64(features, idx) \
+ vhost_features_u64(features, ARRAY_SIZE(features), idx)
+
+#define DEFINE_VHOST_FEATURES_ARRAY_ENTRY(idx, features) \
+ [idx] = VHOST_FEATURES_U64(features, idx),
+
+#define DEFINE_VHOST_FEATURES_ARRAY(array, features) \
+ u64 array[VIRTIO_FEATURES_U64S] = { \
+ UNROLL(VIRTIO_FEATURES_U64S, \
+ DEFINE_VHOST_FEATURES_ARRAY_ENTRY, features) \
+ }

/**
* vhost_vq_set_backend - Set backend.
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ae01457ea2cd..16662f2b87c1 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -29,12 +29,14 @@
*/
#define VHOST_VSOCK_PKT_WEIGHT 256

-enum {
- VHOST_VSOCK_FEATURES = VHOST_FEATURES |
- (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
- (1ULL << VIRTIO_VSOCK_F_SEQPACKET)
+static const int vhost_vsock_features[] = {
+ VHOST_FEATURES,
+ VIRTIO_F_ACCESS_PLATFORM,
+ VIRTIO_VSOCK_F_SEQPACKET
};

+#define VHOST_VSOCK_FEATURES VHOST_FEATURES_U64(vhost_vsock_features, 0)
+
enum {
VHOST_VSOCK_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
};
--
MST