From: Michael Kelley Date: Mon, 8 Jun 2026 02:06:16 +0000 (-0700) Subject: Drivers: hv: vmbus: Set DMA coherent mask for VMBus devices X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ab96bc97cdcf77c6f38634c73d00074c4f92c324;p=thirdparty%2Flinux.git Drivers: hv: vmbus: Set DMA coherent mask for VMBus devices In current code, the coherent_dma_mask for VMBus devices is not set, so it has the default value of 0, which essentially means "invalid". Because drivers for VMBus devices do not use dma_alloc_*() functions, the usual use of the coherent mask does not occur, and no errors result. However, a valid coherent_dma_mask may be needed even though the drivers don't use dma_alloc_*() functions. In a CoCo VM, the VMBus storvsc and netvsc drivers must bounce buffer DMA operations through the swiotlb because the Hyper-V host can't DMA into encrypted guest memory. If the kernel is built with CONFIG_SWIOTLB_DYNAMIC and the initial swiotlb size is small, swiotlb code may need to grow the swiotlb in response to a DMA mapping request. That growth first allocates a transient pool while the swiotlb is expanded in the background. The transient pool memory is allocated from the DMA atomic pools, and the allocation code checks for a valid coherent_dma_mask. With current code, this check fails, then the DMA mapping request from the storvsc or netvsc driver fails, and finally an I/O error occurs. Fix this problem by setting coherent_dma_mask for VMBus devices at the same time that dma_mask is set. Being a synthetic bus, VMBus does not have any restrictions on coherent DMA, so the coherent mask is set to the full 64 bits for all VMBus devices, just like with dma_mask. Signed-off-by: Michael Kelley Signed-off-by: Wei Liu --- diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 23206640c613..a6b9a33db657 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -2169,6 +2169,7 @@ int vmbus_device_register(struct hv_device *child_device_obj) child_device_obj->device.dma_parms = &child_device_obj->dma_parms; child_device_obj->device.dma_mask = &child_device_obj->dma_mask; dma_set_mask(&child_device_obj->device, DMA_BIT_MASK(64)); + dma_set_coherent_mask(&child_device_obj->device, DMA_BIT_MASK(64)); /* * Register with the LDM. This will kick off the driver/device