intel_iommu: support snoop control

SC is required for some kernel features like vhost-vDPA. So this patch
implements basic SC feature. The idea is pretty simple, for software
emulated DMA it would be always coherent. In this case we can simple
advertise ECAP_SC bit. For VFIO and vhost, thing will be more much
complicated, so this patch simply fail the IOMMU notifier
registration.

In the future, we may want to have a dedicated notifiers flag or
similar mechanism to demonstrate the coherency so VFIO could advertise
that if it has VFIO_DMA_CC_IOMMU, for vhost kernel backend we don't
need that since it's a software backend.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220214060346.72455-1-jasowang@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 4c6c016388..32471a44cb 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3030,6 +3030,13 @@ static int vtd_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
     VTDAddressSpace *vtd_as = container_of(iommu, VTDAddressSpace, iommu);
     IntelIOMMUState *s = vtd_as->iommu_state;
 
+    /* TODO: add support for VFIO and vhost users */
+    if (s->snoop_control) {
+        error_setg_errno(errp, -ENOTSUP,
+                         "Snoop Control with vhost or VFIO is not supported");
+        return -ENOTSUP;
+    }
+
     /* Update per-address-space notifier flags */
     vtd_as->notifier_flags = new;
 
@@ -3113,6 +3120,7 @@ static Property vtd_properties[] = {
                       VTD_HOST_ADDRESS_WIDTH),
     DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode, FALSE),
     DEFINE_PROP_BOOL("x-scalable-mode", IntelIOMMUState, scalable_mode, FALSE),
+    DEFINE_PROP_BOOL("snoop-control", IntelIOMMUState, snoop_control, false),
     DEFINE_PROP_BOOL("dma-drain", IntelIOMMUState, dma_drain, true),
     DEFINE_PROP_END_OF_LIST(),
 };
@@ -3643,7 +3651,7 @@ static void vtd_init(IntelIOMMUState *s)
     vtd_spte_rsvd_large[3] = VTD_SPTE_LPAGE_L3_RSVD_MASK(s->aw_bits,
                                                          x86_iommu->dt_supported);
 
-    if (s->scalable_mode) {
+    if (s->scalable_mode || s->snoop_control) {
         vtd_spte_rsvd[1] &= ~VTD_SPTE_SNP;
         vtd_spte_rsvd_large[2] &= ~VTD_SPTE_SNP;
         vtd_spte_rsvd_large[3] &= ~VTD_SPTE_SNP;
@@ -3674,6 +3682,10 @@ static void vtd_init(IntelIOMMUState *s)
         s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_SLTS;
     }
 
+    if (s->snoop_control) {
+        s->ecap |= VTD_ECAP_SC;
+    }
+
     vtd_reset_caches(s);
 
     /* Define registers with default values and bit semantics */