[RFCv1 3/7] x86/kvm: Make DMA pages shared

["Kirill A. Shutemov" <kirill@shutemov.name>]

Make force_dma_unencrypted() return true for KVM to get DMA pages mapped
as shared.

__set_memory_enc_dec() now informs the host via hypercall if the state
of the page has changed from shared to private or back.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/Kconfig                 |  1 +
 arch/x86/mm/mem_encrypt_common.c |  5 +++--
 arch/x86/mm/pat/set_memory.c     | 10 ++++++++++
 include/uapi/linux/kvm_para.h    |  1 +
 4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2b4ce1722dbd..d197b3beb904 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -811,6 +811,7 @@ config KVM_GUEST
 	select PARAVIRT_CLOCK
 	select ARCH_CPUIDLE_HALTPOLL
 	select X86_HV_CALLBACK_VECTOR
+	select X86_MEM_ENCRYPT_COMMON
 	default y
 	help
 	  This option enables various optimizations for running under the KVM
diff --git a/arch/x86/mm/mem_encrypt_common.c b/arch/x86/mm/mem_encrypt_common.c
index dd791352f73f..6bf0718bb72a 100644
--- a/arch/x86/mm/mem_encrypt_common.c
+++ b/arch/x86/mm/mem_encrypt_common.c
@@ -10,14 +10,15 @@
 #include <linux/mm.h>
 #include <linux/mem_encrypt.h>
 #include <linux/dma-direct.h>
+#include <asm/kvm_para.h>
 
 /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
 bool force_dma_unencrypted(struct device *dev)
 {
 	/*
-	 * For SEV, all DMA must be to unencrypted/shared addresses.
+	 * For SEV and KVM, all DMA must be to unencrypted/shared addresses.
 	 */
-	if (sev_active())
+	if (sev_active() || kvm_mem_protected())
 		return true;
 
 	/*
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 16f878c26667..4b312d80033d 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -16,6 +16,7 @@
 #include <linux/pci.h>
 #include <linux/vmalloc.h>
 #include <linux/libnvdimm.h>
+#include <linux/kvm_para.h>
 
 #include <asm/e820/api.h>
 #include <asm/processor.h>
@@ -1977,6 +1978,15 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
 	struct cpa_data cpa;
 	int ret;
 
+	if (kvm_mem_protected()) {
+		/* TODO: Unsharing memory back */
+		if (WARN_ON_ONCE(enc))
+			return -ENOSYS;
+
+		return kvm_hypercall2(KVM_HC_MEM_SHARE,
+				      __pa(addr) >> PAGE_SHIFT, numpages);
+	}
+
 	/* Nothing to do if memory encryption is not active */
 	if (!mem_encrypt_active())
 		return 0;
diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
index 1a216f32e572..09d36683ee0a 100644
--- a/include/uapi/linux/kvm_para.h
+++ b/include/uapi/linux/kvm_para.h
@@ -30,6 +30,7 @@
 #define KVM_HC_SEND_IPI			10
 #define KVM_HC_SCHED_YIELD		11
 #define KVM_HC_ENABLE_MEM_PROTECTED	12
+#define KVM_HC_MEM_SHARE		13
 
 /*
  * hypercalls use architecture specific
-- 
2.26.3