Re: [PATCH] x86/hvm: add HVM-specific Kconfig

[Denis Mukhin <dmkhn@xxxxxxxxx>]

On Monday, March 10th, 2025 at 3:36 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:

> 
> 
> On 07.02.2025 23:03, dmkhn@xxxxxxxxx wrote:
> 
> > Add separate menu for configuring HVM build-time settings to help organizing
> > HVM-specific options.
> > 
> > Signed-off-by: Denis Mukhin dmukhin@xxxxxxxx
> 
> 
> I think it would be nice if "organizing" was further qualified, to really see
> why the change is being made. A particular benefit that Roger points out is
> that this way all HVM-dependent options moved here will then appear in a sub-
> menu like fashion in the tool.
> 
> > --- a/xen/arch/x86/Kconfig
> > +++ b/xen/arch/x86/Kconfig
> > @@ -30,7 +30,6 @@ config X86
> > select HAS_SCHED_GRANULARITY
> > select HAS_UBSAN
> > select HAS_VMAP
> > - select HAS_VPCI if HVM
> > select NEEDS_LIBELF
> 
> 
> As said before, personally I'd prefer if this didn't move.

Fixed in v2, sorry overlooked that.

> 
> > --- /dev/null
> > +++ b/xen/arch/x86/hvm/Kconfig
> > @@ -0,0 +1,73 @@
> > +menuconfig HVM
> > + bool "HVM support"
> > + depends on !PV_SHIM_EXCLUSIVE
> > + default !PV_SHIM
> > + select COMPAT
> > + select HAS_VPCI
> > + select IOREQ_SERVER
> > + select MEM_ACCESS_ALWAYS_ON
> > + help
> > + Interfaces to support HVM domains. HVM domains require hardware
> > + virtualisation extensions (e.g. Intel VT-x, AMD SVM), but can boot
> > + guests which have no specific Xen knowledge.
> > +
> > + This option is needed if you want to run HVM or PVH domains.
> > +
> > + If unsure, say Y.
> > +
> > +if HVM
> > +
> > +config AMD_SVM
> > + bool "AMD-V" if EXPERT
> > + default y
> > + help
> > + Enables virtual machine extensions on platforms that implement the
> > + AMD Virtualization Technology (AMD-V).
> > + If your system includes a processor with AMD-V support, say Y.
> > + If in doubt, say Y.
> > +
> > +config INTEL_VMX
> > + bool "Intel VT-x" if EXPERT
> > + default y
> > + select ARCH_VCPU_IOREQ_COMPLETION
> > + help
> > + Enables virtual machine extensions on platforms that implement the
> > + Intel Virtualization Technology (Intel VT-x).
> > + If your system includes a processor with Intel VT-x support, say Y.
> > + If in doubt, say Y.
> 
> 
> Perhaps not to be done right here, but still: I guess the "default" of these
> want to change to use AMD / INTEL respectively. While we permit enabling the
> virt extension support separately, generally there's little point doing so
> by default when the corresponding CPU support code was disabled.

Addressed.

> 
> > +config ALTP2M
> > + bool "Alternate P2M support" if EXPERT
> > + depends on INTEL_VMX
> > + default y
> > + help
> > + Alternate-p2m allows a guest to manage multiple p2m guest physical
> > + "memory views" (as opposed to a single p2m).
> > + Useful for memory introspection.
> > +
> > + If unsure, stay with defaults.
> > +
> > +config MEM_PAGING
> > + bool "Xen memory paging support (UNSUPPORTED)" if UNSUPPORTED
> > +
> > +config MEM_SHARING
> > + bool "Xen memory sharing support (UNSUPPORTED)" if UNSUPPORTED
> > +
> > +config HVM_FEP
> > + bool "HVM Forced Emulation Prefix support (UNSUPPORTED)" if UNSUPPORTED
> > + default DEBUG
> > + help
> > + Compiles in a feature that allows HVM guest to arbitrarily
> > + exercise the instruction emulator.
> > +
> > + This feature can only be enabled during boot time with
> > + appropriate hypervisor command line option. Please read
> > + hypervisor command line documentation before trying to use
> > + this feature.
> > +
> > + This is strictly for testing purposes, and not appropriate
> > + for use in production.
> > +
> > + If unsure, say N.
> 
> 
> Please can this move ahead of at least the two MEM_* ones, maybe even ahead
> of ALTP2M?

Done.

> 
> Jan