[PATCH] intel_iommu: support snoop control

[Jason Wang <jasowang@redhat.com>]

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>
---
 hw/i386/intel_iommu.c          | 14 +++++++++++++-
 hw/i386/intel_iommu_internal.h |  1 +
 include/hw/i386/intel_iommu.h  |  1 +
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 5b865ac08c..5fa8e361b8 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3022,6 +3022,13 @@ 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;
 
@@ -3105,6 +3112,7 @@ 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(),
 };
@@ -3635,7 +3643,7 @@ 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;
@@ -3666,6 +3674,10 @@ 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 */
diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
index a6c788049b..1ff13b40f9 100644
--- a/hw/i386/intel_iommu_internal.h
+++ b/hw/i386/intel_iommu_internal.h
@@ -188,6 +188,7 @@
 #define VTD_ECAP_IR                 (1ULL << 3)
 #define VTD_ECAP_EIM                (1ULL << 4)
 #define VTD_ECAP_PT                 (1ULL << 6)
+#define VTD_ECAP_SC                 (1ULL << 7)
 #define VTD_ECAP_MHMV               (15ULL << 20)
 #define VTD_ECAP_SRS                (1ULL << 31)
 #define VTD_ECAP_SMTS               (1ULL << 43)
diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
index 41783ee46d..3b5ac869db 100644
--- a/include/hw/i386/intel_iommu.h
+++ b/include/hw/i386/intel_iommu.h
@@ -228,6 +228,7 @@ struct IntelIOMMUState {
 
     bool caching_mode;              /* RO - is cap CM enabled? */
     bool scalable_mode;             /* RO - is Scalable Mode supported? */
+    bool snoop_control;             /* RO - is SNP filed supported? */
 
     dma_addr_t root;                /* Current root table pointer */
     bool root_scalable;             /* Type of root table (scalable or not) */
-- 
2.25.1