[Qemu-devel] [PATCH v2 11/20] hw/virtio: Access MemoryRegion with MemOp

[<tony.nguyen@bt.com>]

On 17/07/19 08:06, Paolo Bonzini wrote:

> My main concern is that MO_BE/MO_LE/MO_TE do not really apply to the
> memory.c paths.  MO_BSWAP is never passed into the MemOp, even if target
> endianness != host endianness.
>
> Therefore, you could return MO_TE | MO_{8,16,32,64} from this function,
> and change memory_region_endianness_inverted to test
> HOST_WORDS_BIGENDIAN instead of TARGET_WORDS_BIGENDIAN.  Then the two
> MO_BSWAPs (one from MO_TE, one from adjust_endianness because
> memory_region_endianness_inverted returns true) cancel out if the
> memory region's endianness is the same as the host's but different
> from the target's.
>
> Some care is needed in virtio_address_space_write and zpci_write_bar.  I
> think the latter is okay, while the former could do something like this:
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index ce928f2429..61885f020c 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -541,16 +541,16 @@ void virtio_address_space_write(VirtIOPCIProxy *proxy,
> hwaddr addr,
>          val = pci_get_byte(buf);
>          break;
>      case 2:
> -        val = cpu_to_le16(pci_get_word(buf));
> +        val = pci_get_word(buf);
>          break;
>      case 4:
> -        val = cpu_to_le32(pci_get_long(buf));
> +        val = pci_get_long(buf);
>          break;
>      default:
>          /* As length is under guest control, handle illegal values. */
>          return;
>      }
> -    memory_region_dispatch_write(mr, addr, val, len, MEMTXATTRS_UNSPECIFIED);
> +    memory_region_dispatch_write(mr, addr, val, size_memop(len) & ~MO_BSWAP,
> MEMTXATTRS_UNSPECIFIED);
>  }
>
>  static void

Sorry Paolo, I noted the need to take care in virtio_address_space_write and
zpci_write_bar but did not understand.

> Some care is needed in virtio_address_space_write and zpci_write_bar.
Is this advice for my v1 implementation, or in the case of the
MO_TE | MO_{8,16,32,64} idead suggested in the paragraph before?

Signed-off-by: Tony Nguyen <tony.nguyen@bt.com>
---
 hw/virtio/virtio-pci.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index ce928f2..265f066 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -17,6 +17,7 @@

 #include "qemu/osdep.h"

+#include "exec/memop.h"
 #include "standard-headers/linux/virtio_pci.h"
 #include "hw/virtio/virtio.h"
 #include "hw/pci/pci.h"
@@ -550,7 +551,8 @@ void virtio_address_space_write(VirtIOPCIProxy *proxy, hwaddr addr,
         /* As length is under guest control, handle illegal values. */
         return;
     }
-    memory_region_dispatch_write(mr, addr, val, len, MEMTXATTRS_UNSPECIFIED);
+    memory_region_dispatch_write(mr, addr, val, SIZE_MEMOP(len),
+                                 MEMTXATTRS_UNSPECIFIED);
 }

 static void
@@ -573,7 +575,8 @@ virtio_address_space_read(VirtIOPCIProxy *proxy, hwaddr addr,
     /* Make sure caller aligned buf properly */
     assert(!(((uintptr_t)buf) & (len - 1)));

-    memory_region_dispatch_read(mr, addr, &val, len, MEMTXATTRS_UNSPECIFIED);
+    memory_region_dispatch_read(mr, addr, &val, SIZE_MEMOP(len),
+                                MEMTXATTRS_UNSPECIFIED);
     switch (len) {
     case 1:
         pci_set_byte(buf, val);
--
1.8.3.1