Re: [XEN PATCH v1 2/3] x86/hvm: introduce config option for stdvga emulation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Oct 04, 2024 at 02:08:10PM -0700, Stefano Stabellini wrote:
> On Fri, 4 Oct 2024, Roger Pau Monné wrote:
> > On Fri, Oct 04, 2024 at 12:33:53PM +0300, Sergiy Kibrik wrote:
> > > Introduce config option X86_STDVGA so that stdvga emulation driver can 
> > > later be
> > > made configurable and be disabled on systems that don't need it.
> > > 
> > > As a first step the option is hidden from user. No functional changes 
> > > intended.
> > > 
> > > Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
> > > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > > ---
> > >  xen/arch/x86/Kconfig              | 3 +++
> > >  xen/arch/x86/hvm/Makefile         | 2 +-
> > >  xen/arch/x86/include/asm/domain.h | 3 ++-
> > >  xen/arch/x86/include/asm/hvm/io.h | 4 ++++
> > >  4 files changed, 10 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> > > index 95275dc17e..89c42ff6da 100644
> > > --- a/xen/arch/x86/Kconfig
> > > +++ b/xen/arch/x86/Kconfig
> > > @@ -147,6 +147,9 @@ config INTEL_VMX
> > >  config X86_PMTIMER
> > >   def_bool HVM
> > >  
> > > +config X86_STDVGA
> > > + def_bool HVM
> > 
> > Same as previous patch, the content of patch 3 needs to be moved here.
> > 
> > > +
> > >  config XEN_SHSTK
> > >   bool "Supervisor Shadow Stacks"
> > >   depends on HAS_AS_CET_SS
> > > diff --git a/xen/arch/x86/hvm/Makefile b/xen/arch/x86/hvm/Makefile
> > > index 321241f0bf..b7741b0f60 100644
> > > --- a/xen/arch/x86/hvm/Makefile
> > > +++ b/xen/arch/x86/hvm/Makefile
> > > @@ -22,7 +22,7 @@ obj-$(CONFIG_X86_PMTIMER) += pmtimer.o
> > >  obj-y += quirks.o
> > >  obj-y += rtc.o
> > >  obj-y += save.o
> > > -obj-y += stdvga.o
> > > +obj-$(CONFIG_X86_STDVGA) += stdvga.o
> > >  obj-y += vioapic.o
> > >  obj-y += vlapic.o
> > >  obj-y += vm_event.o
> > > diff --git a/xen/arch/x86/include/asm/domain.h 
> > > b/xen/arch/x86/include/asm/domain.h
> > > index 3f65bfd190..675a13d917 100644
> > > --- a/xen/arch/x86/include/asm/domain.h
> > > +++ b/xen/arch/x86/include/asm/domain.h
> > > @@ -501,7 +501,8 @@ struct arch_domain
> > >  #define has_vrtc(d)        (!!((d)->arch.emulation_flags & X86_EMU_RTC))
> > >  #define has_vioapic(d)     (!!((d)->arch.emulation_flags & 
> > > X86_EMU_IOAPIC))
> > >  #define has_vpic(d)        (!!((d)->arch.emulation_flags & X86_EMU_PIC))
> > > -#define has_vvga(d)        (!!((d)->arch.emulation_flags & X86_EMU_VGA))
> > > +#define has_vvga(d)        (IS_ENABLED(CONFIG_X86_STDVGA) && \
> > 
> > You don't need the IS_ENABLED() if emulation_flags_ok() is adjusted
> > accordingly.
> 
> Same as patch #1 regarding compiler DCE, we could either do this or
> define X86_EMU_VGA to zero

Yup, seen that.  Defining iX86_EMU_VGA to 0 would be my preference,
like it's done for the !CONFIG_HVM case.

Note however, that like has_vpm(), has_vvga() is only used in the file
that this patch makes optional from the build.

Thanks, Roger.