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

[Tianyu Lan]

On Thu, Apr 9, 2026 at 12:55 AM Easwar Hariharan
<easwar.hariharan@xxxxxxxxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxx>
> > ---
> >  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?
>

Hi Easwar:
     Thanks for your review. AFAIK, storvsc support the capability
We may add such change for netvsc driver later once netvsc
also supports confidential external memory.

-- 
Thanks
Tianyu Lan