Fix incorrect interruptibility_state before vmx entry.

According to SDM 26.3.1.5 Checks on Guest Non-Register State, Bit 0
(blocking by STI) must be 0 if the IF flag (bit 9) is 0 in the RFLAGS
field.
There is an issue during snapshot loading, that IF and
interruptibility_state don't pass the checks, which will result in
VM-entry failure due to invalid guest state.
This WA correct the bit so that vmx entry check could pass. The normal
interruptibility_state update is done when advancing the IP.
In future, proper approach is expected to replace the WA.

Signed-off-by: Colin Xu <colin.xu@intel.com>

core/include/vmx.h

@@ -502,6 +502,12 @@ enum {
     GAS_CSTATE      = 4
 };
 
+// Intel SDM Vol. 3C: Table 24-3. Format of Interruptibility State
+#define GUEST_INTRSTAT_STI_BLOCKING            0x00000001
+#define GUEST_INTRSTAT_SS_BLOCKING             0x00000002
+#define GUEST_INTRSTAT_SMI_BLOCKING            0x00000004
+#define GUEST_INTRSTAT_NMI_BLOCKING            0x00000008
+
 #ifdef HAX_COMPILER_MSVC
 #pragma pack(push, 1)
 #endif

core/intr_exc.c

@@ -121,12 +121,15 @@ uint hax_intr_is_blocked(struct vcpu_t *vcpu)
 {
     struct vcpu_state_t *state = vcpu->state;
     uint32_t intr_status;
+    uint32_t intr_blocking = 0;
 
     if (!(state->_eflags & EFLAGS_IF))
         return 1;
 
+    intr_blocking |= GUEST_INTRSTAT_STI_BLOCKING;
+    intr_blocking |= GUEST_INTRSTAT_SS_BLOCKING;
     intr_status = vmx(vcpu, interruptibility_state).raw;
-    if (intr_status & 3)
+    if (intr_status & intr_blocking)
         return 1;
     return 0;
 }

core/vcpu.c

@@ -1078,7 +1078,27 @@ static void load_dirty_vmcs_fields(struct vcpu_t *vcpu)
         vcpu->rflags_dirty = 0;
     }
 
-    // interruptibility
+    /*
+     * interruptibility
+     * 26.3.1.5 Checks on Guest Non-Register State
+     * Bit 0 (blocking by STI) must be 0 if the IF flag (bit 9) is 0 in the
+     *   RFLAGS field.
+     * This is a WA to fix the VM-entry failure due to invalid guest state,
+     *   sometimes when a snapshot is loaded but IF and interruptibility_state
+     *   don't pass the checks as mentioned in SDM 26.3.1.5.
+     * In in-order execution, interruptibility_state is updated when advancing
+     *   the IP. However when a snapshot is loaded, EFLAGS are restored but
+     *   guest non-register state not restored.
+     *   TODO: Find better approach instead of letting the check pass.
+     */
+    if (!(state->_rflags & EFLAGS_IF)) {
+        if (vmx(vcpu, interruptibility_state).raw &
+            GUEST_INTRSTAT_STI_BLOCKING) {
+            vmx(vcpu, interruptibility_state).raw &=
+                    ~GUEST_INTRSTAT_STI_BLOCKING;
+            vcpu->interruptibility_dirty = 1;
+        }
+    }
     if (vcpu->interruptibility_dirty) {
         vmwrite(vcpu, GUEST_INTERRUPTIBILITY,
                 vmx(vcpu, interruptibility_state).raw);
@@ -1747,9 +1767,12 @@ static void advance_rip(struct vcpu_t *vcpu)
 {
     struct vcpu_state_t *state = vcpu->state;
     uint32_t interruptibility = vmx(vcpu, interruptibility_state).raw;
+    uint32_t intr_blocking = 0;
 
-    if (interruptibility & 3u) {
-        interruptibility &= ~3u;
+    intr_blocking |= GUEST_INTRSTAT_STI_BLOCKING;
+    intr_blocking |= GUEST_INTRSTAT_SS_BLOCKING;
+    if (interruptibility & intr_blocking) {
+        interruptibility &= ~intr_blocking;
         vmx(vcpu, interruptibility_state).raw = interruptibility;
         vcpu->interruptibility_dirty = 1;
     }