Re: [PATCH v5 05/10] x86emul: support MOVDIR64B insn

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/03/2020 12:34, Jan Beulich wrote:
> Introduce a new blk() hook, paralleling the rmw() on in certain way, but
> being intended for larger data sizes, and hence its HVM intermediate
> handling function doesn't fall back to splitting the operation if the
> requested virtual address can't be mapped.
>
> Note that SDM revision 071 doesn't specify exception behavior for
> ModRM.mod == 0b11; assuming #UD here.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

> ---
> TBD: If we want to avoid depending on correct MTRR settings,
>      hvmemul_map_linear_addr() may need to gain a parameter to allow
>      controlling cachability of the produced mapping(s). Of course the
>      function will also need to be made capable of mapping at least
>      p2m_mmio_direct pages for this and the two ENQCMD insns to be
>      actually useful.

MOVDIR64B isn't the first instruction to demonstrate this corner case,
but we do need to organise something to solve this problem.  I'm
confident it will cause real memory corruption issue for encrypted
memory VMs under introspection.