Add an "is_bigendian" flag to the kvm_run.mmio structure.
This is needed for architectures that can make both little- and
big-endian memory accesses.
Signed-off-by: Hollis Blanchard <[EMAIL PROTECTED]>
---
PowerPC has different instructions for native and byte-reversed memory
accesses, and some implementations can also can map individual pages as
byte-reversed. Right now in the PowerPC KVM implementation the kernel
detects byte-reversed MMIO from the guest and converts the data as
appropriate so that userland only ever deals with big-endian data.
That's fine and all, but I started thinking about supporting MMIO
passthrough, in which userland wouldn't emulate an MMIO at all, but
rather execute it on the real hardware (via mmap /dev/mem, for example).
In that case, it's actually very important that the endianness of the
access be preserved, since we need that information to access the real
hardware.
I don't think this patch has any serious x86 ABI implications, since
current x86 code just ignores the flag. I guess x86 could continue to
ignore it in the future, or it could explicitly zero the new flag.
Comments?
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -123,6 +123,7 @@ struct kvm_run {
__u8 data[8];
__u32 len;
__u8 is_write;
+ __u8 is_bigendian;
} mmio;
/* KVM_EXIT_HYPERCALL */
struct {
--
Hollis Blanchard
IBM Linux Technology Center
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