Re: [PATCH v3 2/2] Drivers: hv: Introduce mshv_vtl driver

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

On Fri, May 23, 2025 at 02:55:32PM +0530, Naman Jain wrote:
> 
> 
> On 5/22/2025 11:40 PM, Stanislav Kinsburskii wrote:
> > On Wed, May 21, 2025 at 11:33:29AM +0530, Naman Jain wrote:
> > > 
> > > 
> > > On 5/21/2025 12:25 AM, Stanislav Kinsburskii wrote:
> > > > On Mon, May 19, 2025 at 10:26:42AM +0530, Naman Jain wrote:
> > > > > Provide an interface for Virtual Machine Monitor like OpenVMM and its
> > > > > use as OpenHCL paravisor to control VTL0 (Virtual trust Level).
> > > > > Expose devices and support IOCTLs for features like VTL creation,
> > > > > VTL0 memory management, context switch, making hypercalls,
> > > > > mapping VTL0 address space to VTL2 userspace, getting new VMBus
> > > > > messages and channel events in VTL2 etc.
> > > > > 
> > > > > Co-developed-by: Roman Kisel <romank@linux.microsoft.com>
> > > > > Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> > > > > Co-developed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > > > > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > > > > Reviewed-by: Roman Kisel <romank@linux.microsoft.com>
> > > > > Reviewed-by: Alok Tiwari <alok.a.tiwari@oracle.com>
> > > > > Message-ID: <20250512140432.2387503-3-namjain@linux.microsoft.com>
> > > > > Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> > > > > ---
> > > > >    drivers/hv/Kconfig          |   20 +
> > > > >    drivers/hv/Makefile         |    7 +-
> > > > >    drivers/hv/mshv_vtl.h       |   52 +
> > > > >    drivers/hv/mshv_vtl_main.c  | 1783 +++++++++++++++++++++++++++++++++++
> > > > >    include/hyperv/hvgdk_mini.h |   81 ++
> > > > >    include/hyperv/hvhdk.h      |    1 +
> > > > >    include/uapi/linux/mshv.h   |   82 ++
> > > > >    7 files changed, 2025 insertions(+), 1 deletion(-)
> > > > >    create mode 100644 drivers/hv/mshv_vtl.h
> > > > >    create mode 100644 drivers/hv/mshv_vtl_main.c
> > > > > 
> > > > > diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> > > > > index eefa0b559b73..21cee5564d70 100644
> > > > > --- a/drivers/hv/Kconfig
> > > > > +++ b/drivers/hv/Kconfig
> > > > > @@ -72,4 +72,24 @@ config MSHV_ROOT
> > > > >    	  If unsure, say N.
> > > > > +config MSHV_VTL
> > > > > +	tristate "Microsoft Hyper-V VTL driver"
> > > > > +	depends on HYPERV && X86_64
> > > > > +	depends on TRANSPARENT_HUGEPAGE
> > > > 
> > > > Why does it depend on TRANSPARENT_HUGEPAGE?
> > > > 
> > > 
> > 
> > Let me rephrase: can this driver work without transparent huge pages?
> > If yes, then it shouldn't depend on the option and rather select it.
> > If not, then it should be either fixed to be able to or have an
> > expalanation why this dependecy was introduced.
> 
> No, it won't work. Reason being - we are adding support to map VTL0 address
> space to a user-mode process in VTL2. VTL2 for OpenHCL makes use of Huge
> pages to improve performance on VMs having large memory requirements. Thus,
> we need TRANSPARENT_HUGEPAGE.
> 
> I will add this as a comment in Kconfig.
> 

Then I'd suggest selecting huge pages instead of depending on them: it's
kinda weird that one need to select huge pages first to be able to
even find out, that there is some virtualization driver, depending on it.

Thanks,
Stanislav