Re: [PATCH] x86/VMBus: Confidential VMBus for dynamic DMA transfers

[Easwar Hariharan <easwar.hariharan@linux.microsoft.com>]

On 4/8/2026 12:31 AM, Tianyu Lan wrote:
> Hyper-V provides Confidential VMBus to communicate between
> device model and device guest driver via encrypted/private
> memory in Confidential VM. The device model is in OpenHCL
> (https://openvmm.dev/guide/user_guide/openhcl.html) that
> plays the paravisor role.
> 
> For a VMBus device, there are two communication methods to
> talk with Host/Hypervisor. 1) VMBUS Ring buffer 2) Dynamic
> DMA transfer.
> 
> The Confidential VMBus Ring buffer has been upstreamed by
> Roman Kisel(commit 6802d8af47d1).
> 
> The dynamic DMA transition of VMBus device normally goes
> through DMA core and it uses SWIOTLB as bounce buffer in
> a CoCo VM.
> 
> The Confidential VMBus device can do DMA directly to
> private/encrypted memory. Because the swiotlb is decrypted
> memory, the DMA transfer must not be bounced through the
> swiotlb, so as to preserve confidentiality. This is different
> from the default for Linux CoCo VMs, so not use DMA(SWIOTLB)
> API in VMBus driver when confidential dynamic DMA transfers
> capability is present.
> 
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
>  drivers/scsi/storvsc_drv.c | 28 +++++++++++++++++++++-------
>  include/linux/hyperv.h     |  1 +
>  2 files changed, 22 insertions(+), 7 deletions(-)
> 

Does netvsc not need this same sort of patch?

Thanks,
Easwar (he/him)