[PATCH v9 13/23] x86/virt/seamldr: Abort updates after a failed step

[Chao Gao <chao.gao@intel.com>]

A TDX module update is a multi-step process, and any step can fail.

The current update flow continues to later steps after an error.
Continuing after a failure can leave the TDX module in an unrecoverable
state.

One failure case must remain recoverable: update contention with an ongoing
TD build. The agreed kernel behavior for this case [1] is to fail the
update with -EBUSY so userspace can retry later.

Abort the update on any failure. This also makes the TD-build contention
case recoverable, because that failure occurs before any TDX module state
is changed. Apply the same rule to all errors instead of special-casing
-EBUSY.

Track per-step failures, stop the update loop once a failure is observed,
and do not advance the state machine to the next step.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Xu Yilun <yilun.xu@linux.intel.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Link: https://lore.kernel.org/linux-coco/aQFmOZCdw64z14cJ@google.com/ # [1]
---
v9:
  - Avoid nested if/else by deferring failure accounting to ack_state().
  - Reduce indentation of the main flow.
  - Convert the failed flag into a counter. This avoids a conditional
    update of the flag; the counter can simply accumulate failures.
---
 arch/x86/virt/vmx/tdx/seamldr.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
index 7befe4a08f33..48fe71319fea 100644
--- a/arch/x86/virt/vmx/tdx/seamldr.c
+++ b/arch/x86/virt/vmx/tdx/seamldr.c
@@ -170,6 +170,7 @@ enum module_update_state {
 static struct update_ctrl {
 	enum module_update_state state;
 	int num_ack;
+	int num_failed;
 	/*
 	 * Protect update_ctrl. Raw spinlock as it will be acquired from
 	 * interrupt-disabled contexts.
@@ -187,12 +188,13 @@ static void __set_target_state(struct update_ctrl *ctrl,
 }
 
 /* Last one to ack a state moves to the next state. */
-static void ack_state(struct update_ctrl *ctrl)
+static void ack_state(struct update_ctrl *ctrl, int result)
 {
 	raw_spin_lock(&ctrl->lock);
 
+	ctrl->num_failed += !!result;
 	ctrl->num_ack++;
-	if (ctrl->num_ack == num_online_cpus())
+	if (ctrl->num_ack == num_online_cpus() && !ctrl->num_failed)
 		__set_target_state(ctrl, ctrl->state + 1);
 
 	raw_spin_unlock(&ctrl->lock);
@@ -202,6 +204,7 @@ static void init_state(struct update_ctrl *ctrl)
 {
 	raw_spin_lock_init(&ctrl->lock);
 	__set_target_state(ctrl, MODULE_UPDATE_START + 1);
+	ctrl->num_failed = 0;
 }
 
 /*
@@ -228,8 +231,8 @@ static int do_seamldr_install_module(void *seamldr_params)
 			break;
 		}
 
-		ack_state(&update_ctrl);
-	} while (curstate != MODULE_UPDATE_DONE);
+		ack_state(&update_ctrl, ret);
+	} while (curstate != MODULE_UPDATE_DONE && !READ_ONCE(update_ctrl.num_failed));
 
 	return ret;
 }
-- 
2.52.0