[Qemu-devel] [PATCH] virtio-pci: Fix endianness of virtio config

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

The virtio config area in PIO space is a bit special. The initial
header is little endian but the rest (device specific) is guest
native endian.

The PIO accessors for PCI on machines that don't have native IO ports
assume that all PIO is little endian, which works fine for everything
except the above.

A complicated way to fix it would be to split the BAR into two memory
regions with different endianess settings, but this isn't practical
to do, besides, the PIO code doesn't honor region endianness anyway
(I have a patch for that too but it isn't necessary at this stage).

So I decided to go for the quick fix instead which consists of
reverting the swap in virtio-pci in selected places, hoping that when
we eventually do a "v2" of the virtio protocols, we sort that out once
and for all using a fixed endian setting for everything.

Unfortunately, that mean moving virtio-pci from Makefile.objs to
Makefile.target so we can use TARGET_WORDS_BIGENDIAN which would
otherwise be poisoned.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 Makefile.objs   |    1 -
 Makefile.target |    1 +
 hw/virtio-pci.c |   24 ++++++++++++++++++++++--
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/Makefile.objs b/Makefile.objs
index 4f6d26c..b721fca 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -186,7 +186,6 @@ hw-obj-y =
 hw-obj-y += vl.o loader.o
 hw-obj-$(CONFIG_VIRTIO) += virtio-console.o
 hw-obj-y += usb-libhw.o
-hw-obj-$(CONFIG_VIRTIO_PCI) += virtio-pci.o
 hw-obj-y += fw_cfg.o
 hw-obj-$(CONFIG_PCI) += pci.o pci_bridge.o
 hw-obj-$(CONFIG_PCI) += msix.o msi.o
diff --git a/Makefile.target b/Makefile.target
index ef6834b..03d44c3 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -191,6 +191,7 @@ obj-y = arch_init.o cpus.o monitor.o machine.o gdbstub.o balloon.o ioport.o
 # need to fix this properly
 obj-$(CONFIG_NO_PCI) += pci-stub.o
 obj-$(CONFIG_VIRTIO) += virtio.o virtio-blk.o virtio-balloon.o virtio-net.o virtio-serial-bus.o
+obj-$(CONFIG_VIRTIO_PCI) += virtio-pci.o
 obj-y += vhost_net.o
 obj-$(CONFIG_VHOST_NET) += vhost.o
 obj-$(CONFIG_REALLY_VIRTFS) += 9pfs/virtio-9p-device.o
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 77b75bc..ca70e42 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -412,20 +412,34 @@ static uint32_t virtio_pci_config_readw(void *opaque, uint32_t addr)
 {
     VirtIOPCIProxy *proxy = opaque;
     uint32_t config = VIRTIO_PCI_CONFIG(&proxy->pci_dev);
+    uint16_t val;
     if (addr < config)
         return virtio_ioport_read(proxy, addr);
     addr -= config;
-    return virtio_config_readw(proxy->vdev, addr);
+    val = virtio_config_readw(proxy->vdev, addr);
+#ifdef TARGET_WORDS_BIGENDIAN
+    /* virtio is odd, ioports are LE but config space is target native
+     * endian. However, in qemu, all PIO is LE, so we need to re-swap
+     * on BE targets
+     */
+    val = bswap16(val);
+#endif
+    return val;
 }
 
 static uint32_t virtio_pci_config_readl(void *opaque, uint32_t addr)
 {
     VirtIOPCIProxy *proxy = opaque;
     uint32_t config = VIRTIO_PCI_CONFIG(&proxy->pci_dev);
+    uint32_t val;
     if (addr < config)
         return virtio_ioport_read(proxy, addr);
     addr -= config;
-    return virtio_config_readl(proxy->vdev, addr);
+    val = virtio_config_readl(proxy->vdev, addr);
+#ifdef TARGET_WORDS_BIGENDIAN
+    val = bswap32(val);
+#endif
+    return val;
 }
 
 static void virtio_pci_config_writeb(void *opaque, uint32_t addr, uint32_t val)
@@ -449,6 +463,9 @@ static void virtio_pci_config_writew(void *opaque, uint32_t addr, uint32_t val)
         return;
     }
     addr -= config;
+#ifdef TARGET_WORDS_BIGENDIAN
+    val = bswap16(val);
+#endif
     virtio_config_writew(proxy->vdev, addr, val);
 }
 
@@ -461,6 +478,9 @@ static void virtio_pci_config_writel(void *opaque, uint32_t addr, uint32_t val)
         return;
     }
     addr -= config;
+#ifdef TARGET_WORDS_BIGENDIAN
+    val = bswap32(val);
+#endif
     virtio_config_writel(proxy->vdev, addr, val);
 }