Re: [PATCH v7 07/13] confidential guest support: Introduce cgs "ready" flag

Greg Kurz
2021-01-14T09:15:35Z

On Thu, 14 Jan 2021 10:58:05 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> The platform specific details of mechanisms for implementing
> confidential guest support may require setup at various points during
> initialization. Thus, it's not really feasible to have a single cgs
> initialization hook, but instead each mechanism needs its own
> initialization calls in arch or machine specific code.
>
> However, to make it harder to have a bug where a mechanism isn't
> properly initialized under some circumstances, we want to have a
> common place, relatively late in boot, where we verify that cgs has
> been initialized if it was requested.
>
> This patch introduces a ready flag to the ConfidentialGuestSupport
> base type to accomplish this, which we verify just before the machine
> specific initialization function.
>

Since this is a strong requirement for any new cgs implementation, I
guess it could be advertised a bit more with some extra documentation
in the confidential-guest-support.h header file as well.

Anyway,

Reviewed-by: Greg Kurz <groug@kaod.org>

Unrelated. I've just spotted mdroth@linux.vnet.ibm.com in the Cc list
of this thread, but, as you know, Mike is now working on other topics
at AMD :)

> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> hw/core/machine.c | 8 ++++++++
> include/exec/confidential-guest-support.h | 2 ++
> target/i386/sev.c | 2 ++
> 3 files changed, 12 insertions(+)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 94194ab82d..5a7433332b 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -1190,6 +1190,14 @@ void machine_run_board_init(MachineState *machine)
> }
>
> if (machine->cgs) {
> + /*
> + * Where confidential guest support is initialized depends on
> + * the specific mechanism in use. But, we need to make sure
> + * it's ready by now. If it isn't, that's a bug in the
> + * implementation of that cgs mechanism.
> + */
> + assert(machine->cgs->ready);
> +
> /*
> * With confidential guests, the host can't see the real
> * contents of RAM, so there's no point in it trying to merge
> diff --git a/include/exec/confidential-guest-support.h b/include/exec/confidential-guest-support.h
> index 5f131023ba..bcaf6c9f49 100644
> --- a/include/exec/confidential-guest-support.h
> +++ b/include/exec/confidential-guest-support.h
> @@ -27,6 +27,8 @@ OBJECT_DECLARE_SIMPLE_TYPE(ConfidentialGuestSupport, CONFIDENTIAL_GUEST_SUPPORT)
>
> struct ConfidentialGuestSupport {
> Object parent;
> +
> + bool ready;
> };
>
> typedef struct ConfidentialGuestSupportClass {
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index e2b41ef342..3d94635397 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -737,6 +737,8 @@ int sev_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
> qemu_add_machine_init_done_notifier(&sev_machine_done_notify);
> qemu_add_vm_change_state_handler(sev_vm_state_change, sev);
>
> + cgs->ready = true;
> +
> return 0;
> err:
> sev_guest = NULL;