x86, kvm: common confidential computing subset

[PATCH 11/26] runstate: skip initial CPU reset if reset is not actually possible

Posted by Paolo Bonzini 1 year, 10 months ago

Right now, the system reset is concluded by a call to
cpu_synchronize_all_post_reset() in order to sync any changes
that the machine reset callback applied to the CPU state.

However, for VMs with encrypted state such as SEV-ES guests (currently
the only case of guests with non-resettable CPUs) this cannot be done,
because guest state has already been finalized by machine-init-done notifiers.
cpu_synchronize_all_post_reset() does nothing on these guests, and actually
we would like to make it fail if called once guest has been encrypted.
So, assume that boards that support non-resettable CPUs do not touch
CPU state and that all such setup is done before, at the time of
cpu_synchronize_all_post_init().

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 system/runstate.c | 15 ++++++++++++++-
 roms/edk2         |  2 +-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/system/runstate.c b/system/runstate.c
index d6ab860ecaa..cb4905a40fc 100644
--- a/system/runstate.c
+++ b/system/runstate.c
@@ -501,7 +501,20 @@ void qemu_system_reset(ShutdownCause reason)
     default:
         qapi_event_send_reset(shutdown_caused_by_guest(reason), reason);
     }
-    cpu_synchronize_all_post_reset();
+
+    /*
+     * Some boards use the machine reset callback to point CPUs to the firmware
+     * entry point.  Assume that this is not the case for boards that support
+     * non-resettable CPUs (currently used only for confidential guests), in
+     * which case cpu_synchronize_all_post_init() is enough because
+     * it does _more_  than cpu_synchronize_all_post_reset().
+     */
+    if (cpus_are_resettable()) {
+        cpu_synchronize_all_post_reset();
+    } else {
+        assert(runstate_check(RUN_STATE_PRELAUNCH));
+    }
+
     vm_set_suspended(false);
 }
 
diff --git a/roms/edk2 b/roms/edk2
index edc6681206c..819cfc6b42a 160000
--- a/roms/edk2
+++ b/roms/edk2
@@ -1 +1 @@
-Subproject commit edc6681206c1a8791981a2f911d2fb8b3d2f5768
+Subproject commit 819cfc6b42a68790a23509e4fcc58ceb70e1965e
-- 
2.44.0

Re: [PATCH 11/26] runstate: skip initial CPU reset if reset is not actually possible

Posted by Philippe Mathieu-Daudé 1 year, 10 months ago

On 22/3/24 19:11, Paolo Bonzini wrote:
> Right now, the system reset is concluded by a call to
> cpu_synchronize_all_post_reset() in order to sync any changes
> that the machine reset callback applied to the CPU state.
> 
> However, for VMs with encrypted state such as SEV-ES guests (currently
> the only case of guests with non-resettable CPUs) this cannot be done,
> because guest state has already been finalized by machine-init-done notifiers.
> cpu_synchronize_all_post_reset() does nothing on these guests, and actually
> we would like to make it fail if called once guest has been encrypted.
> So, assume that boards that support non-resettable CPUs do not touch
> CPU state and that all such setup is done before, at the time of
> cpu_synchronize_all_post_init().
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   system/runstate.c | 15 ++++++++++++++-
>   roms/edk2         |  2 +-
Without submodule change:
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

>   2 files changed, 15 insertions(+), 2 deletions(-)

Re: [PATCH 11/26] runstate: skip initial CPU reset if reset is not actually possible

Posted by Daniel P. Berrangé 1 year, 10 months ago

On Fri, Mar 22, 2024 at 07:11:01PM +0100, Paolo Bonzini wrote:
> Right now, the system reset is concluded by a call to
> cpu_synchronize_all_post_reset() in order to sync any changes
> that the machine reset callback applied to the CPU state.
> 
> However, for VMs with encrypted state such as SEV-ES guests (currently
> the only case of guests with non-resettable CPUs) this cannot be done,
> because guest state has already been finalized by machine-init-done notifiers.
> cpu_synchronize_all_post_reset() does nothing on these guests, and actually
> we would like to make it fail if called once guest has been encrypted.
> So, assume that boards that support non-resettable CPUs do not touch
> CPU state and that all such setup is done before, at the time of
> cpu_synchronize_all_post_init().
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  system/runstate.c | 15 ++++++++++++++-
>  roms/edk2         |  2 +-
>  2 files changed, 15 insertions(+), 2 deletions(-)

Accidental submodule change here :

> diff --git a/roms/edk2 b/roms/edk2
> index edc6681206c..819cfc6b42a 160000
> --- a/roms/edk2
> +++ b/roms/edk2
> @@ -1 +1 @@
> -Subproject commit edc6681206c1a8791981a2f911d2fb8b3d2f5768
> +Subproject commit 819cfc6b42a68790a23509e4fcc58ceb70e1965e
> -- 
> 2.44.0
> 
> 

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|