Re: [PATCH v1 15/26] s390: Add functions to query arm guest time

[Andreas Grapentin]

On Jun 01 26, Oliver Upton wrote:
> > Add functions to convert between ARM guest time (LSB0) and s390 host
> > time (MSB0) using new ptff function codes.
> > 
> > Co-developed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> > Signed-off-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> > Signed-off-by: Steffen Eiden <seiden@xxxxxxxxxxxxx>
> > ---
> >  arch/s390/include/asm/timex.h | 49 +++++++++++++++++++++++++++++++++++
> >  arch/s390/kernel/time.c       |  1 +
> >  arch/s390/kvm/arm64/arm.c     |  9 ++++++-
> >  3 files changed, 58 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
> > index 49447b40f038..9ec22a28bbda 100644
> > --- a/arch/s390/include/asm/timex.h
> > +++ b/arch/s390/include/asm/timex.h
> > @@ -99,6 +99,8 @@ extern unsigned char ptff_function_mask[16];
> >  #define PTFF_QSI	0x02	/* query steering information */
> >  #define PTFF_QPT	0x03	/* query physical clock */
> >  #define PTFF_QUI	0x04	/* query UTC information */
> > +#define PTFF_QAGTO	0x10	/* query arm guest time offset */
> > +#define PTFF_QAGPT	0x11	/* query arm guest physical time offset */
> 
> Are these analogous to CNTVOFF_EL2 and CNTPOFF_EL2?

They are somewhat related -- we don't have the EL2 counter offset
registers, but we still need to virtualize the guest counters, so
instead we have to maintain the guest counter offset separately.

However, to determine the correct guest counter offset, we are using
these new PTFF function codes to translate between the s390 and arm64
architected counter domains.

Best,
Andreas