[RFC PATCH 3/3] RFC: KVM: x86: support KVM_CAP_DMA_MEM

[Chia-I Wu]

When a memslot has KVM_MEM_DMA set, we want VMX_EPT_IPAT_BIT cleared
for the memslot.  Before that is possible, simply call
kvm_arch_register_noncoherent_dma for the memslot.

SVM does not have the ignore-pat bit.  Guest PAT is always honored.

Signed-off-by: Chia-I Wu <olvaffe at gmail.com>
Cc: Gurchetan Singh <gurchetansingh at chromium.org>
Cc: Gerd Hoffmann <kraxel at redhat.com>
---
 arch/x86/include/uapi/asm/kvm.h | 1 +
 arch/x86/kvm/x86.c              | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 503d3f42da16..578b686e3880 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -48,6 +48,7 @@
 #define __KVM_HAVE_XSAVE
 #define __KVM_HAVE_XCRS
 #define __KVM_HAVE_READONLY_MEM
+#define __KVM_HAVE_DMA_MEM
 
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fb5d64ebc35d..c89a4647fef6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3331,6 +3331,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_GET_TSC_KHZ:
 	case KVM_CAP_KVMCLOCK_CTRL:
 	case KVM_CAP_READONLY_MEM:
+	case KVM_CAP_DMA_MEM:
 	case KVM_CAP_HYPERV_TIME:
 	case KVM_CAP_IOAPIC_POLARITY_IGNORED:
 	case KVM_CAP_TSC_DEADLINE_TIMER:
@@ -10045,6 +10046,11 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 */
 	if (change != KVM_MR_DELETE)
 		kvm_mmu_slot_apply_flags(kvm, (struct kvm_memory_slot *) new);
+
+	if (change == KVM_MR_CREATE && new->flags & KVM_MEM_DMA)
+		kvm_arch_register_noncoherent_dma(kvm);
+	else if (change == KVM_MR_DELETE && old->flags & KVM_MEM_DMA)
+		kvm_arch_unregister_noncoherent_dma(kvm);
 }
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
-- 
2.25.0.265.gbab2e86ba0-goog