VFIO exposes BARs to user space as a byte stream so userspace can
read it using pread()/pwrite(). Since this is a byte stream, VFIO should
not do byte swapping and simply return values as it gets them from
PCI device.
Instead, the existing code assumes that byte stream in read/write is
little-endian and it fixes endianness for values which it passes to
ioreadXX/iowriteXX helpers. This works for little-endian as PCI is
little endian and le32_to_cpu/... are stubs.
This also works for big endian but rather by an accident: it reads 4 bytes
from the stream (@val is big endian), converts to CPU format (which should
be big endian) as it was little endian (@val becomes actually little
endian) and calls iowrite32() which does not do swapping on big endian
system.
This removes byte swapping and makes use ioread32be/iowrite32be
(and 16bit versions) on big-endian systems. The "be" helpers take
native endian values and do swapping at the moment of writing to a PCI
register using one of "store byte-reversed" instructions.
Suggested-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
drivers/vfio/pci/vfio_pci_rdwr.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
index 210db24..f363b5a 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -21,6 +21,18 @@
#include "vfio_pci_private.h"
+#ifdef __BIG_ENDIAN__
+#define ioread16_native ioread16be
+#define ioread32_native ioread32be
+#define iowrite16_native iowrite16be
+#define iowrite32_native iowrite32be
+#else
+#define ioread16_native ioread16
+#define ioread32_native ioread32
+#define iowrite16_native iowrite16
+#define iowrite32_native iowrite32
+#endif
+
/*
* Read or write from an __iomem region (MMIO or I/O port) with an excluded
* range which is inaccessible. The excluded range drops writes and fills
@@ -50,9 +62,9 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
if (copy_from_user(&val, buf, 4))
return -EFAULT;
- iowrite32(le32_to_cpu(val), io + off);
+ iowrite32_native(val, io + off);
} else {
- val = cpu_to_le32(ioread32(io + off));
+ val = ioread32_native(io + off);
if (copy_to_user(buf, &val, 4))
return -EFAULT;
@@ -66,9 +78,9 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
if (copy_from_user(&val, buf, 2))
return -EFAULT;
- iowrite16(le16_to_cpu(val), io + off);
+ iowrite16_native(val, io + off);
} else {
- val = cpu_to_le16(ioread16(io + off));
+ val = ioread16_native(io + off);
if (copy_to_user(buf, &val, 2))
return -EFAULT;
--
2.0.0
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