Re: [PATCH v3 5/5] x86/Kconfig: Add HYPERV_VTL_MODE

[Saurabh Singh Sengar <ssengar@linux.microsoft.com>]

On Sun, Mar 26, 2023 at 03:16:15PM +0000, Michael Kelley (LINUX) wrote:
> From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Monday, March 20, 2023 3:04 AM
> > 
> > Add HYPERV_VTL_MODE Kconfig flag for VTL mode.
> > 
> > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > ---
> >  arch/x86/Kconfig         | 24 ++++++++++++++++++++++++
> >  arch/x86/hyperv/Makefile |  1 +
> >  2 files changed, 25 insertions(+)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 453f462f6c9c..c3faaaea1e31 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -782,6 +782,30 @@ menuconfig HYPERVISOR_GUEST
> > 
> >  if HYPERVISOR_GUEST
> > 
> > +config HYPERV_VTL_MODE
> > +	bool "Enable Linux to boot in VTL context"
> > +	depends on X86_64 && HYPERV
> > +	default n
> > +	help
> > +	  Virtual Secure Mode (VSM) is a set of hypervisor capabilities and
> > +	  enlightenments offered to host and guest partitions which enables
> > +	  the creation and management of new security boundaries within
> > +	  operating system software.
> > +
> > +	  VSM achieves and maintains isolation through Virtual Trust Levels
> > +	  (VTLs). Virtual Trust Levels are hierarchical, with higher levels
> > +	  being more privileged than lower levels. VTL0 is the least privileged
> > +	  level, and currently only other level supported is VTL2.
> > +
> > +	  Select this option to build a Linux kernel to run at a VTL other than
> > +	  the normal VTL0, which currently is only VTL2.  This option
> > +	  initializes the x86 platform for VTL2, and adds the ability to boot
> > +	  secondary CPUs directly into 64-bit context as required for VTLs other
> > +	  than 0.  A kernel built with this option must run at VTL2, and will
> > +	  not run as a normal guest.
> > +
> > +	  If unsure, say N
> > +
> 
> Is there a reason for putting this in arch/x86/Kconfig instead of in
> drivers/hv/Kconfig under the "Microsoft Hyper-V guest support"
> menu with the other Hyper-V settings?  It seems like grouping
> this with the other Hyper-V settings would make it easier to find,
> unless there's some reason that doesn't work.

As all the code dependent on this flag is in arch/x86/hyperv, and all
other kernel flags used in arch/x86/hyperv/Makefile are define in
arch/x86/Kconfig, arch/x86/Kconfig was my default choice.

But your suggestion makes perfect sense, I will move it to
drivers/hv/Kconfig

Regards,
Saurabh

> 
> Michael
> 
> >  config PARAVIRT
> >  	bool "Enable paravirtualization code"
> >  	depends on HAVE_STATIC_CALL
> > diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
> > index 5d2de10809ae..3a1548054b48 100644
> > --- a/arch/x86/hyperv/Makefile
> > +++ b/arch/x86/hyperv/Makefile
> > @@ -1,6 +1,7 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >  obj-y			:= hv_init.o mmu.o nested.o irqdomain.o ivm.o
> >  obj-$(CONFIG_X86_64)	+= hv_apic.o hv_proc.o
> > +obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o
> > 
> >  ifdef CONFIG_X86_64
> >  obj-$(CONFIG_PARAVIRT_SPINLOCKS)	+= hv_spinlock.o
> > --
> > 2.34.1