Fix Guest/VM and Host extension status sync-up

When transitioning from virt-on (VS/VU) to virt-off (HS/M) we should
mark Host extension status (i.e. FS, VS, and XS bits) as dirty when
Guest/VM extension status is dirty and Host extension status is
initial, clean, or dirty.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

riscv/processor.cc

@@ -647,17 +647,24 @@ void processor_t::set_virt(bool virt)
     if (state.v and !virt) {
       /*
        * When transitioning from virt-on (VS/VU) to virt-off (HS/M)
-       * we should sync Guest/VM FS, VS, and XS state with Host FS,
-       * VS, and XS state.
+       * we should mark Host extension status (i.e. FS, VS, and XS
+       * bits) as dirty when Guest/VM extension status is dirty and
+       * Host extension status is initial, clean, or dirty.
        */
-      state.vsstatus &= ~SSTATUS_FS;
-      state.vsstatus |= (state.mstatus & SSTATUS_FS);
-      if (supports_extension('V')) {
-        state.vsstatus &= ~SSTATUS_VS;
-        state.vsstatus |= (state.mstatus & SSTATUS_VS);
+      if ((state.vsstatus & SSTATUS_FS) &&
+          ((state.mstatus & SSTATUS_FS) == SSTATUS_FS)) {
+        state.vsstatus |= SSTATUS_FS;
       }
-      state.vsstatus &= ~SSTATUS_XS;
-      state.vsstatus |= (state.mstatus & SSTATUS_XS);
+      if (supports_extension('V') &&
+          (state.vsstatus & SSTATUS_VS) &&
+          ((state.mstatus & SSTATUS_VS) == SSTATUS_VS)) {
+        state.vsstatus |= SSTATUS_VS;
+      }
+      if ((state.vsstatus & SSTATUS_XS) &&
+          ((state.mstatus & SSTATUS_XS) == SSTATUS_XS)) {
+        state.vsstatus |= SSTATUS_XS;
+      }
+      /* Update SD bit of Host */
       state.vsstatus &= (xlen == 64 ? ~SSTATUS64_SD : ~SSTATUS32_SD);
       if (((state.mstatus & SSTATUS_FS) == SSTATUS_FS) ||
           ((state.vsstatus & SSTATUS_VS) == SSTATUS_VS) ||