Re: [Qemu-devel] [PATCH 2/2] WHPX: register for unrecognized MSR exits

[Paolo Bonzini]

On 06/06/2018 00:15, Justin Terry (VM) wrote:
> Some variations of Linux kernels end up accessing MSR's that the Windows
> Hypervisor doesn't implement which causes a GP to be returned to the guest.
> This fix registers QEMU for unimplemented MSR access and globally returns 0 on
> reads and ignores writes. This behavior is allows the Linux kernel to probe 
> the
> MSR with a write/read/check sequence it does often without failing the access.
> 
> Signed-off-by: Justin Terry (VM) <address@hidden>
> ---
>  target/i386/whpx-all.c | 41 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 38 insertions(+), 3 deletions(-)

Hmm, KVM tries to list the MSRs that Linux (or Windows :)) use.  It can
do the full whitelist, but it's opt-in.

Recent Linux kernels also are generally less picky about #GPs from MSRs,
so I don't think a generic whitelist is a good idea.  If the
"non-hosted" Hyper-V is doing the same that would be fine I guess, but
then there should probably be a comment about it in the code.

While this is discussed a bit more, I've queued patch 1.

Thanks,

Paolo