hv:disable iommu snoop control to enable gvt-d by an option

If one of the enabled VT-d DMAR units
doesn’t support snoop control,
then bit 11 of leaf PET of EPT is not set,
since the field is treated as reserved(0)
by VT-d hardware implementations
not supporting snoop control.

GUP IOMMU doesn’t support snoop control,
this patch add an option to disable
iommu snoop control for gvt-d.

v2 -> v3:
        * refine the MICRO name and description.

Tracked-On: #4405

Signed-off-by: Junming Liu <junming.liu@intel.com>
Reviewed-by: Wu Binbin <binbin.wu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/arch/x86/Kconfig

@@ -340,3 +340,10 @@ config MCE_ON_PSC_WORKAROUND_DISABLED
 	  conditionally applied to the models that may be affected by the issue. However,
 	  the software workaround has negative impact on performance. If all the guest OS
 	  kernels are trusted, this option may be set for performance.
+
+config IOMMU_ENFORCE_SNP
+	bool "IOMMU enforce snoop behavior of DMA operation"
+	default n
+	help
+	  GPU IOMMU doesn't support snoop control capability,
+	  To enable gvt-d,disable IOMMU snoop control by default.

hypervisor/arch/x86/vtd.c

@@ -1263,7 +1263,17 @@ struct iommu_domain *create_iommu_domain(uint16_t vm_id, uint64_t translation_ta
 		domain->trans_table_ptr = translation_table;
 		domain->addr_width = addr_width;
 		domain->is_tt_ept = true;
+
+#ifdef CONFIG_IOMMU_ENFORCE_SNP
 		domain->iommu_snoop = true;
+#else
+		/* TODO: GPU IOMMU doesn't have snoop control capbility,
+		 * so set domain->iommu_snoop false to enable gvt-d by default.
+		 * If want to refine iommu snoop control policy,
+		 * need to change domain->iommu_snoop dynamically.
+		 */
+		domain->iommu_snoop = false;
+#endif
 
 		dev_dbg(DBG_LEVEL_IOMMU, "create domain [%d]: vm_id = %hu, ept@0x%x",
 			vmid_to_domainid(domain->vm_id), domain->vm_id, domain->trans_table_ptr);