Drivers: hv: vmbus: Propagate VMbus coherence to each VMbus device

VMbus synthetic devices are not represented in the ACPI DSDT -- only
the top level VMbus device is represented. As a result, on ARM64
coherence information in the _CCA method is not specified for
synthetic devices, so they default to not hardware coherent.
Drivers for some of these synthetic devices have been recently
updated to use the standard DMA APIs, and they are incurring extra
overhead of unneeded software coherence management.

Fix this by propagating coherence information from the VMbus node
in ACPI to the individual synthetic devices. There's no effect on
x86/x64 where devices are always hardware coherent.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/1648138492-2191-2-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

2 files changed, 42 insertions, 0 deletions

diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 181d16bbf49d..820e81406251 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -20,6 +20,7 @@
 #include <linux/panic_notifier.h>
 #include <linux/ptrace.h>
 #include <linux/slab.h>
+#include <linux/dma-map-ops.h>
 #include <asm/hyperv-tlfs.h>
 #include <asm/mshyperv.h>
 
@@ -216,6 +217,16 @@ bool hv_query_ext_cap(u64 cap_query)
 }
 EXPORT_SYMBOL_GPL(hv_query_ext_cap);
 
+void hv_setup_dma_ops(struct device *dev, bool coherent)
+{
+	/*
+	 * Hyper-V does not offer a vIOMMU in the guest
+	 * VM, so pass 0/NULL for the IOMMU settings
+	 */
+	arch_setup_dma_ops(dev, 0, 0, NULL, coherent);
+}
+EXPORT_SYMBOL_GPL(hv_setup_dma_ops);
+
 bool hv_is_hibernation_supported(void)
 {
 	return !hv_root_partition && acpi_sleep_state_supported(ACPI_STATE_S4);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 6c057c76c2ca..3cd0d3a44fa2 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -921,6 +921,21 @@ static int vmbus_probe(struct device *child_device)
 }
 
 /*
+ * vmbus_dma_configure -- Configure DMA coherence for VMbus device
+ */
+static int vmbus_dma_configure(struct device *child_device)
+{
+	/*
+	 * On ARM64, propagate the DMA coherence setting from the top level
+	 * VMbus ACPI device to the child VMbus device being added here.
+	 * On x86/x64 coherence is assumed and these calls have no effect.
+	 */
+	hv_setup_dma_ops(child_device,
+		device_get_dma_attr(&hv_acpi_dev->dev) == DEV_DMA_COHERENT);
+	return 0;
+}
+
+/*
  * vmbus_remove - Remove a vmbus device
  */
 static void vmbus_remove(struct device *child_device)
@@ -1040,6 +1055,7 @@ static struct bus_type  hv_bus = {
 	.remove =		vmbus_remove,
 	.probe =		vmbus_probe,
 	.uevent =		vmbus_uevent,
+	.dma_configure =	vmbus_dma_configure,
 	.dev_groups =		vmbus_dev_groups,
 	.drv_groups =		vmbus_drv_groups,
 	.bus_groups =		vmbus_bus_groups,
@@ -2435,6 +2451,21 @@ static int vmbus_acpi_add(struct acpi_device *device)
 
 	hv_acpi_dev = device;
 
+	/*
+	 * Older versions of Hyper-V for ARM64 fail to include the _CCA
+	 * method on the top level VMbus device in the DSDT. But devices
+	 * are hardware coherent in all current Hyper-V use cases, so fix
+	 * up the ACPI device to behave as if _CCA is present and indicates
+	 * hardware coherence.
+	 */
+	ACPI_COMPANION_SET(&device->dev, device);
+	if (IS_ENABLED(CONFIG_ACPI_CCA_REQUIRED) &&
+	    device_get_dma_attr(&device->dev) == DEV_DMA_NOT_SUPPORTED) {
+		pr_info("No ACPI _CCA found; assuming coherent device I/O\n");
+		device->flags.cca_seen = true;
+		device->flags.coherent_dma = true;
+	}
+
 	result = acpi_walk_resources(device->handle, METHOD_NAME__CRS,
 					vmbus_walk_resources, NULL);