[PATCH v2 06/14] hv: vmbus: cover all shared-page policy combinations

[Emerson Busson <emersonbusson@gmail.com>]

Name the shared-page selection and enumerate all eight combinations of
Hyper-V isolation, independent guest-memory encryption and channel
confidentiality. Either platform visibility signal selects shared
backing; the confidential-channel override keeps private backing. These
are decision tests, not confidential hardware qualification.

Signed-off-by: Emerson Busson <emersonbusson@gmail.com>
---
 drivers/hv/channel.c           | 16 ++++++++++++++--
 drivers/hv/hyperv_vmbus.h      |  2 ++
 drivers/hv/vmbus_buffer_test.c | 29 +++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 0c025a12808a..8ed155f2669f 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -45,6 +45,13 @@ int vmbus_buffer_round_size(u32 size, u32 *rounded_size)
 	return 0;
 }
 
+bool
+vmbus_needs_shared_pages(bool hv_isolation, bool guest_mem_encrypted,
+			 bool confidential)
+{
+	return !confidential && (hv_isolation || guest_mem_encrypted);
+}
+
 unsigned int vmbus_buffer_order(unsigned long remaining,
 				unsigned int max_order)
 {
@@ -837,6 +844,8 @@ static void *__vmbus_alloc_buffer(struct vmbus_channel *channel,
 	unsigned long nr_pages;
 	unsigned long remaining;
 	unsigned long page_idx = 0;
+	bool hv_isolation;
+	bool guest_mem_encrypted;
 	struct page **chunks = NULL;
 	struct page **pages = NULL;
 	unsigned int order = MAX_PAGE_ORDER;
@@ -853,9 +862,12 @@ static void *__vmbus_alloc_buffer(struct vmbus_channel *channel,
 	nr_pages = rounded_size >> PAGE_SHIFT;
 	remaining = nr_pages;
 
+	hv_isolation = hv_is_isolation_supported();
+	guest_mem_encrypted = cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT);
+
 	/* If the buffer does not need to be decrypted, just use vzalloc() */
-	if ((!hv_is_isolation_supported() &&
-	     !cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) || confidential)
+	if (!vmbus_needs_shared_pages(hv_isolation, guest_mem_encrypted,
+				      confidential))
 		return vzalloc(rounded_size);
 
 	/* Worst case: every chunk is a single page. */
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index e08c472041d5..06094000f2f1 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -557,6 +557,8 @@ int hv_remove_ring_sysfs(struct vmbus_channel *channel);
  * These are shared with vmbus_buffer_test.c, which is built into the
  * hv_vmbus object alongside channel.c. They stay unexported.
  */
+bool vmbus_needs_shared_pages(bool hv_isolation, bool guest_mem_encrypted,
+			      bool confidential);
 int vmbus_buffer_round_size(u32 size, u32 *rounded_size);
 unsigned int vmbus_buffer_order(unsigned long remaining,
 				unsigned int max_order);
diff --git a/drivers/hv/vmbus_buffer_test.c b/drivers/hv/vmbus_buffer_test.c
index 60fc526af1af..9b401ef2ceea 100644
--- a/drivers/hv/vmbus_buffer_test.c
+++ b/drivers/hv/vmbus_buffer_test.c
@@ -38,6 +38,34 @@ static void vmbus_buffer_size_overflow_test(struct kunit *test)
 			(u32)(U32_MAX - PAGE_SIZE + 1));
 }
 
+static void vmbus_buffer_private_shared_selection_test(struct kunit *test)
+{
+	static const struct {
+		bool isolation;
+		bool encrypted;
+		bool confidential;
+		bool shared;
+	} cases[] = {
+		{ false, false, false, false },
+		{ false, false, true, false },
+		{ false, true, false, true },
+		{ false, true, true, false },
+		{ true, false, false, true },
+		{ true, false, true, false },
+		{ true, true, false, true },
+		{ true, true, true, false },
+	};
+	unsigned int i;
+
+	/* Either platform signal requires visibility; confidential stays private. */
+	for (i = 0; i < ARRAY_SIZE(cases); i++)
+		KUNIT_EXPECT_EQ(test,
+				vmbus_needs_shared_pages(cases[i].isolation,
+							 cases[i].encrypted,
+							 cases[i].confidential),
+				cases[i].shared);
+}
+
 static void vmbus_ring_fallback_order_zero_test(struct kunit *test)
 {
 	unsigned int order;
@@ -317,6 +345,7 @@ static void vmbus_buffer_order_zero_allocation_test(struct kunit *test)
 static struct kunit_case vmbus_buffer_test_cases[] = {
 	KUNIT_CASE(vmbus_buffer_size_rounding_test),
 	KUNIT_CASE(vmbus_buffer_size_overflow_test),
+	KUNIT_CASE(vmbus_buffer_private_shared_selection_test),
 	KUNIT_CASE(vmbus_ring_fallback_order_zero_test),
 	KUNIT_CASE(vmbus_buffer_failed_teardown_leaks_test),
 	KUNIT_CASE(vmbus_buffer_partial_allocation_cleanup_test),
-- 
2.43.0