Fix potential stale

Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>

Author: ludfjig

src/hyperlight_host/src/hypervisor/virtual_machine/whp.rs

@@ -555,6 +555,12 @@ impl VirtualMachine for WhpVm {
         let whp_regs: [(WHV_REGISTER_NAME, Align16<WHV_REGISTER_VALUE>); WHP_SREGS_NAMES_LEN] =
             sregs.into();
 
+        // TODO: Remove this filter and instead fix the callers to pass
+        // the correct APIC_BASE value (e.g. read it from the VP before
+        // the first set_sregs, or use 0xFEE00900 in standard_64bit_defaults).
+        // Filtering here causes AMD/SVM bugs because SVM_CLEAN_FIELD_AVIC
+        // is never dirtied after WHvResetPartition (see reset_partition).
+        //
         // When LAPIC emulation is active (always with hw-interrupts),
         // skip writing APIC_BASE. The generic CommonSpecialRegisters
         // defaults APIC_BASE to 0 which would globally disable the LAPIC.
@@ -730,6 +736,23 @@ impl VirtualMachine for WhpVm {
             #[cfg(feature = "hw-interrupts")]
             Self::init_lapic_bulk(self.partition)
                 .map_err(|e| RegisterError::ResetPartition(e.into()))?;
+
+            // With hw-interrupts, set_sregs filters out APIC_BASE to
+            // avoid disabling the LAPIC (the snapshot sregs default it
+            // to 0). On AMD/SVM this means SVM_CLEAN_FIELD_AVIC is
+            // never dirtied after the VMCB rebuild, causing the CPU to
+            // use stale cached AVIC state on VMRUN which corrupts guest
+            // memory reads. Re-writing APIC_BASE to its post-reset
+            // value forces the dirty bit via ValSetEmulatedApicBase.
+            #[cfg(feature = "hw-interrupts")]
+            {
+                let apic_base = self.sregs()?.apic_base;
+                self.set_registers(&[(
+                    WHvX64RegisterApicBase,
+                    Align16(WHV_REGISTER_VALUE { Reg64: apic_base }),
+                )])
+                .map_err(|e| RegisterError::ResetPartition(e.into()))?;
+            }
         }
         Ok(())
     }