Re: [PATCH v2 3/6] x86/mem-paging: use guest handle for XENMEM_paging_op_prep

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/04/2020 09:38, Jan Beulich wrote:
> While it should have been this way from the beginning, not doing so will
> become an actual problem with PVH Dom0. The interface change is binary
> compatible, but requires tools side producers to be re-built.
>
> Drop the bogus/unnecessary page alignment restriction on the input
> buffer at the same time.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Use HANDLE_64() instead of HANDLE_PARAM() for function parameter.
> ---
> Is there really no way to avoid the buffer copying in libxc?

Not currently no.

Since we now have access to regular kernel memory via mmap() on
/dev/xen/hypercall, we are now in a position where someone could hook up
implement a small memory allocator backed exclusively by mmap()'d pages,
and this would remove all bounce buffering in userspace.

~Andrew