On 09/03/2020, Vitaly Kuznetsov wrote:

Jon Doron [off-list ref] writes:

quoted

Signed-off-by: Jon Doron <redacted>
---
 include/uapi/linux/kvm.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4b95f9a31a2f..24b7c48ccc6f 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h

@@ -197,6 +197,7 @@ struct kvm_hyperv_exit {
 			__u64 msg_page;
 		} synic;
 		struct {
+			__u32 pad;
 			__u64 input;
 			__u64 result;
 			__u64 params[2];

This doesn't seem to be correct, __u64 get aligned at 8 byte boundary so
implicitly you now (pre-patch) have the following:

struct kvm_hyperv_exit {
__u32 type;
       __u32 pad1;
union {
	struct {
		__u32 msr;
                       __u32 pad2;
		__u64 control;
		__u64 evt_page;
		__u64 msg_page;
	} synic;
	struct {
		__u64 input;
		__u64 result;
		__u64 params[2];
	} hcall;
} u;
};

and the suggestion is only to make it explicit. Adding something before
'input' will actually break ABI.

-- 
Vitaly

Bah sorry guys :( not sure why this too so many iterations... will fix 
it right in next version.