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[PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO
From: |
Andre Silva |
Subject: |
[PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO |
Date: |
Wed, 8 Jan 2020 13:16:18 -0300 |
Remove the bswap function calls after reading and before writing
memory bytes in virtio_pci_config_read and virtio_pci_config_write
because they are reverting back an already swapped bytes.
Consider the table below in the context of virtio_pci_config_read
function.
Host Target virtio-config-read[wl]
swap? virtio-is-big-endian? extra bswap?
Should be Final result Final result ok?
----- ------- ------------------------ ----------------------- --------------
----------- -------------- ------------------
LE BE s(x) true s(s(x))
s(x) x No
LE LE x false - x
x Yes
BE LE s(x) false -
s(x) s(x) Yes
BE BE x true s(x) x
s(x) No
In table above, when target is big endian and VirtIO is pre 1.0,
function virtio_is_big_endian would return true and the extra
swap would be executed, reverting the previous swap made by
virtio_config_read[wl].
The 's(x)' means that a swap function was applied at
address x. 'LE' is little endian and 'BE' is big endian. The
'Final result' column is the returned value from
virtio_pci_config_read, considering a target Virtio pre 1.0.
'x' means that target's value was not swapped in Qemu, 's(x)' means
that Qemu will use a swapped value.
If we remove the extra swap made in virtio_pci_config_read we will
have the correct result in any host/target combination, both for
VirtIO pre 1.0 or later versions.
The same reasoning applies to virtio_pci_config_write.
Signed-off-by: Andre Silva <address@hidden>
---
hw/virtio/virtio-pci.c | 12 ------------
1 file changed, 12 deletions(-)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index c6b47a9c73..4ba9e847f3 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -431,15 +431,9 @@ static uint64_t virtio_pci_config_read(void *opaque,
hwaddr addr,
break;
case 2:
val = virtio_config_readw(vdev, addr);
- if (virtio_is_big_endian(vdev)) {
- val = bswap16(val);
- }
break;
case 4:
val = virtio_config_readl(vdev, addr);
- if (virtio_is_big_endian(vdev)) {
- val = bswap32(val);
- }
break;
}
return val;
@@ -465,15 +459,9 @@ static void virtio_pci_config_write(void *opaque, hwaddr
addr,
virtio_config_writeb(vdev, addr, val);
break;
case 2:
- if (virtio_is_big_endian(vdev)) {
- val = bswap16(val);
- }
virtio_config_writew(vdev, addr, val);
break;
case 4:
- if (virtio_is_big_endian(vdev)) {
- val = bswap32(val);
- }
virtio_config_writel(vdev, addr, val);
break;
}
--
2.24.1
- [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Andre Silva, 2020/01/08
- [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO,
Andre Silva <=
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Peter Maydell, 2020/01/08
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, André Silva, 2020/01/09
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Greg Kurz, 2020/01/09
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, André Silva, 2020/01/09
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Greg Kurz, 2020/01/10
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, André Silva, 2020/01/10
- Re: [PATCH] virtio: Prevent double swap due to target pre 1.0 VirtIO, Greg Kurz, 2020/01/10