[PATCH] intel-iommu: Set status bit after operation completed

[Zhenzhong Duan]

According to SDM 11.4.4.2 Global Status Register:
"This field is cleared by hardware when software sets the SRTP field in the
Global Command register. This field is set by hardware when hardware
completes the ‘Set Root Table Pointer’ operation using the value provided
in the Root Table Address register"

Follow above spec to clear then set RTPS after finish all works, this way
helps avoiding potential race with guest kernel. Though linux kernel is
single threaded in writing GCMD_REG and checking GSTS_REG.

Same reasion for GSTS_REG.TES

Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
---
 hw/i386/intel_iommu.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index faade7def8..7cba1945a3 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -2312,11 +2312,12 @@ static void vtd_handle_gcmd_qie(IntelIOMMUState *s, 
bool en)
 /* Set Root Table Pointer */
 static void vtd_handle_gcmd_srtp(IntelIOMMUState *s)
 {
+    vtd_set_clear_mask_long(s, DMAR_GSTS_REG, VTD_GSTS_RTPS, 0);
     vtd_root_table_setup(s);
-    /* Ok - report back to driver */
-    vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_RTPS);
     vtd_reset_caches(s);
     vtd_address_space_refresh_all(s);
+    /* Ok - report back to driver */
+    vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_RTPS);
 }
 
 /* Set Interrupt Remap Table Pointer */
@@ -2338,19 +2339,22 @@ static void vtd_handle_gcmd_te(IntelIOMMUState *s, bool 
en)
 
     if (en) {
         s->dmar_enabled = true;
-        /* Ok - report back to driver */
-        vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_TES);
     } else {
         s->dmar_enabled = false;
 
         /* Clear the index of Fault Recording Register */
         s->next_frcd_reg = 0;
-        /* Ok - report back to driver */
-        vtd_set_clear_mask_long(s, DMAR_GSTS_REG, VTD_GSTS_TES, 0);
     }
 
     vtd_reset_caches(s);
     vtd_address_space_refresh_all(s);
+
+    /* Ok - report back to driver */
+    if (en) {
+        vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_TES);
+    } else {
+        vtd_set_clear_mask_long(s, DMAR_GSTS_REG, VTD_GSTS_TES, 0);
+    }
 }
 
 /* Handle Interrupt Remap Enable/Disable */
-- 
2.25.1