[Xen-devel] Reading HVM guest memory

["Emre Can Sezer" <ecsezer@xxxxxxxx>]

Hi,

I'm trying to pass some information from an HVM guest to the hypervisor. 
The guest kernel allocates a buffer and writes all the necessary stuff in
it.  It then makes a hypercall (hvm_op) to notify Xen of the buffer
location.

My problem is that I can't read the buffer from the hypervisor.  The
pointer is being passed correctly.  I tried copying it to a local buffer
via copy_from_user() function but this function fails.  I noticed that
access_ok() function fails for this pointer, so I tried to use the
__copy_from_user_ll() function.  All to no avail.

How can I read this guest buffer which resides in guest kernel space?

The information I'm trying to pass is simple events like a module being
loaded or a new page allocation.  There are 4 types of events alltogether
so I could make individual hypercalls for each.  But I'm curious why I
cann't read the guest memory.  Also if there is an easier way of passing
information from an HVM guest to Xen, I'd love to hear it.

Thanks in advance.

John

PS. I'm using 64-bit guest.

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