cpu: process pending #HV events when enabling interrupts

Interrupts delivered via #HV are ignored when EFLAGS.IF=0.  When
enabling interrupts, the #HV doorbell page must be checked for pending
events that were suppressed while interrupts were disabled so that they
do not remain pending indefinitely.

Signed-off-by: Jon Lange <[email protected]>

kernel/src/cpu/irq_state.rs

@@ -4,6 +4,7 @@
 //
 // Author: Joerg Roedel <[email protected]>
 
+use crate::cpu::percpu::this_cpu;
 use crate::cpu::{irqs_disable, irqs_enable};
 use core::arch::asm;
 use core::marker::PhantomData;
@@ -32,6 +33,12 @@ pub unsafe fn raw_irqs_disable() {
 #[inline(always)]
 pub unsafe fn raw_irqs_enable() {
     asm!("sti", options(att_syntax, preserves_flags, nomem));
+
+    // Now that interrupts are enabled, process any #HV events that may be
+    // pending.
+    if let Some(doorbell) = this_cpu().hv_doorbell() {
+        doorbell.process_if_required();
+    }
 }
 
 /// Query IRQ state on current CPU

kernel/src/sev/hv_doorbell.rs

@@ -140,6 +140,13 @@ impl HVDoorbell {
         // is performed.
     }
 
+    pub fn process_if_required(&self) {
+        let flags = HVDoorbellFlags::from(self.flags.load(Ordering::Relaxed));
+        if flags.no_further_signal() {
+            self.process_pending_events();
+        }
+    }
+
     pub fn no_eoi_required(&self) -> bool {
         // Check to see if the "no EOI required" flag is set to determine
         // whether an explicit EOI can be avoided.