[Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access

[Rusty Russell]

Virtio is currently defined to work as "guest endian", but this is a
problem if the guest can change endian.  As most targets can't change
endian, we make it a per-target option to avoid pessimising.

This is based on a simpler patch by Anthony Liguouri, which only handled
the vring accesses.  We also need some drivers to access these helpers,
eg. for data which contains headers.

Signed-off-by: Rusty Russell <address@hidden>
---
 hw/virtio/virtio.c                |  46 +++++++++----
 include/hw/virtio/virtio-access.h | 138 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+), 14 deletions(-)
 create mode 100644 include/hw/virtio/virtio-access.h

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 8176c14..2887f17 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -18,6 +18,7 @@
 #include "hw/virtio/virtio.h"
 #include "qemu/atomic.h"
 #include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
 
 /* The alignment to use between consumer and producer parts of vring.
  * x86 pagesize again. */
@@ -84,6 +85,20 @@ struct VirtQueue
     EventNotifier host_notifier;
 };
 
+#ifdef TARGET_VIRTIO_SWAPENDIAN
+bool virtio_byteswap;
+
+/* Ask target code if we should swap endian for all vring and config access. */
+static void mark_endian(void)
+{
+    virtio_byteswap = virtio_swap_endian();
+}
+#else
+static void mark_endian(void)
+{
+}
+#endif
+
 /* virt queue functions */
 static void virtqueue_init(VirtQueue *vq)
 {
@@ -100,49 +115,49 @@ static inline uint64_t vring_desc_addr(hwaddr desc_pa, 
int i)
 {
     hwaddr pa;
     pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, addr);
-    return ldq_phys(pa);
+    return virtio_ldq_phys(pa);
 }
 
 static inline uint32_t vring_desc_len(hwaddr desc_pa, int i)
 {
     hwaddr pa;
     pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, len);
-    return ldl_phys(pa);
+    return virtio_ldl_phys(pa);
 }
 
 static inline uint16_t vring_desc_flags(hwaddr desc_pa, int i)
 {
     hwaddr pa;
     pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, flags);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline uint16_t vring_desc_next(hwaddr desc_pa, int i)
 {
     hwaddr pa;
     pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, next);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline uint16_t vring_avail_flags(VirtQueue *vq)
 {
     hwaddr pa;
     pa = vq->vring.avail + offsetof(VRingAvail, flags);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline uint16_t vring_avail_idx(VirtQueue *vq)
 {
     hwaddr pa;
     pa = vq->vring.avail + offsetof(VRingAvail, idx);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
 {
     hwaddr pa;
     pa = vq->vring.avail + offsetof(VRingAvail, ring[i]);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline uint16_t vring_used_event(VirtQueue *vq)
@@ -154,42 +169,42 @@ static inline void vring_used_ring_id(VirtQueue *vq, int 
i, uint32_t val)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, ring[i].id);
-    stl_phys(pa, val);
+    virtio_stl_phys(pa, val);
 }
 
 static inline void vring_used_ring_len(VirtQueue *vq, int i, uint32_t val)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, ring[i].len);
-    stl_phys(pa, val);
+    virtio_stl_phys(pa, val);
 }
 
 static uint16_t vring_used_idx(VirtQueue *vq)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, idx);
-    return lduw_phys(pa);
+    return virtio_lduw_phys(pa);
 }
 
 static inline void vring_used_idx_set(VirtQueue *vq, uint16_t val)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, idx);
-    stw_phys(pa, val);
+    virtio_stw_phys(pa, val);
 }
 
 static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, flags);
-    stw_phys(pa, lduw_phys(pa) | mask);
+    virtio_stw_phys(pa, virtio_lduw_phys(pa) | mask);
 }
 
 static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask)
 {
     hwaddr pa;
     pa = vq->vring.used + offsetof(VRingUsed, flags);
-    stw_phys(pa, lduw_phys(pa) & ~mask);
+    virtio_stw_phys(pa, virtio_lduw_phys(pa) & ~mask);
 }
 
 static inline void vring_avail_event(VirtQueue *vq, uint16_t val)
@@ -199,7 +214,7 @@ static inline void vring_avail_event(VirtQueue *vq, 
uint16_t val)
         return;
     }
     pa = vq->vring.used + offsetof(VRingUsed, ring[vq->vring.num]);
-    stw_phys(pa, val);
+    virtio_stw_phys(pa, val);
 }
 
 void virtio_queue_set_notification(VirtQueue *vq, int enable)
@@ -525,6 +540,9 @@ void virtio_set_status(VirtIODevice *vdev, uint8_t val)
     VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
     trace_virtio_set_status(vdev, val);
 
+    /* If guest virtio endian is uncertain, set it now. */
+    mark_endian();
+
     if (k->set_status) {
         k->set_status(vdev, val);
     }
diff --git a/include/hw/virtio/virtio-access.h 
b/include/hw/virtio/virtio-access.h
new file mode 100644
index 0000000..b1d531e
--- /dev/null
+++ b/include/hw/virtio/virtio-access.h
@@ -0,0 +1,138 @@
+/*
+ * Virtio Accessor Support: In case your target can change endian.
+ *
+ * Copyright IBM, Corp. 2013
+ *
+ * Authors:
+ *  Rusty Russell   <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+#ifndef _QEMU_VIRTIO_ACCESS_H
+#define _QEMU_VIRTIO_ACCESS_H
+
+#ifdef TARGET_VIRTIO_SWAPENDIAN
+/* Architectures which need biendian define this function. */
+extern bool virtio_swap_endian(void);
+
+extern bool virtio_byteswap;
+#else
+#define virtio_byteswap false
+#endif
+
+static inline uint16_t virtio_lduw_phys(hwaddr pa)
+{
+    if (virtio_byteswap) {
+        return bswap16(lduw_phys(pa));
+    }
+    return lduw_phys(pa);
+    
+}
+
+static inline uint32_t virtio_ldl_phys(hwaddr pa)
+{
+    if (virtio_byteswap) {
+        return bswap32(ldl_phys(pa));
+    }
+    return ldl_phys(pa);
+}
+
+static inline uint64_t virtio_ldq_phys(hwaddr pa)
+{
+    if (virtio_byteswap) {
+        return bswap64(ldq_phys(pa));
+    }
+    return ldq_phys(pa);
+}
+
+static inline void virtio_stw_phys(hwaddr pa, uint16_t value)
+{
+    if (virtio_byteswap) {
+        stw_phys(pa, bswap16(value));
+    } else {
+        stw_phys(pa, value);
+    }
+}
+
+static inline void virtio_stl_phys(hwaddr pa, uint32_t value)
+{
+    if (virtio_byteswap) {
+        stl_phys(pa, bswap32(value));
+    } else {
+        stl_phys(pa, value);
+    }
+}
+
+static inline void virtio_stw_p(void *ptr, uint16_t v)
+{
+    if (virtio_byteswap) {
+       stw_p(ptr, bswap16(v));
+    } else {
+       stw_p(ptr, v);
+    }
+}
+
+static inline void virtio_stl_p(void *ptr, uint32_t v)
+{
+    if (virtio_byteswap) {
+       stl_p(ptr, bswap32(v));
+    } else {
+       stl_p(ptr, v);
+    }
+}
+
+static inline void virtio_stq_p(void *ptr, uint64_t v)
+{
+    if (virtio_byteswap) {
+       stq_p(ptr, bswap64(v));
+    } else {
+       stq_p(ptr, v);
+    }
+}
+
+static inline int virtio_lduw_p(const void *ptr)
+{
+    if (virtio_byteswap) {
+       return bswap16(lduw_p(ptr));
+    } else {
+       return lduw_p(ptr);
+    }
+}
+
+static inline int virtio_ldl_p(const void *ptr)
+{
+    if (virtio_byteswap) {
+       return bswap32(ldl_p(ptr));
+    } else {
+       return ldl_p(ptr);
+    }
+}
+
+static inline uint64_t virtio_ldq_p(const void *ptr)
+{
+    if (virtio_byteswap) {
+       return bswap64(ldq_p(ptr));
+    } else {
+       return ldq_p(ptr);
+    }
+}
+
+static inline uint32_t virtio_tswap32(uint32_t s)
+{
+    if (virtio_byteswap) {
+       return bswap32(tswap32(s));
+    } else {
+       return tswap32(s);
+    }
+}
+
+static inline void virtio_tswap32s(uint32_t *s)
+{
+    tswap32s(s);
+    if (virtio_byteswap) {
+       *s = bswap32(*s);
+    }
+}
+#endif /* _QEMU_VIRTIO_ACCESS_H */
-- 
1.8.1.2