On 6/14/21 2:03 PM, Borislav Petkov wrote:

On Mon, Jun 14, 2021 at 07:45:11AM -0500, Brijesh Singh wrote:

quoted

IMO, there is no need to add a warning. This case should happen if its
either a hypervisor bug or hypervisor does not follow the GHCB
specification. I followed the SEV-ES vmgexit handling  and it does not
warn if the hypervisor returns a wrong response code. We simply
terminate the guest.

This brings my regular user-friendliness question: will the guest user
know what happened or will the guest simply disappear/freeze without any
hint as to what has happened so that a post-mortem analysis would turn
out hard to decipher?

When a guest requests to terminate then guest user (aka VMM) will be
notified through the hypervisor that guest has requested the
termination. KVM defines a fixed set of reason code that is passed to
the guest user, see
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/kvm.h#L237.
In this particular case guest user probably get the KVM_EXIT_SHUTDOWN --
i.e guest asked to be terminated. If user wants to see the actual GHCB
reason code then they must look into the KVM log.

Now that we have to defined a Linux specific reason set, we could
potentially define a new error code "Invalid response code" and return
that instead of generic termination error in this particular case. So
that when user looks at KVM log they see the "invalid response code"
instead of the generic GHCB error.

If we go with that approach then I think it makes sense to cover it for
SEV-ES guests too.

quoted

I did thought about reusing the VMGEXIT defined macro
SNP_PAGE_STATE_{PRIVATE, SHARED} but I was not sure if you will be okay
with that.

Yeah, I think that makes stuff simpler. Unless there's something
speaking against it which we both are not thinking of right now.

quoted

Additionally now both the function name and macro name will
include the "SNP". The call will look like this:

snp_prep_memory(paddr, SNP_PAGE_STATE_PRIVATE)

Yap, looks ok to me.

Thx.