Re: [PATCH 2/9] arm/domain: Get rid of READ/WRITE_SYSREG32

[Julien Grall <julien@xxxxxxx>]

On 21/04/2021 08:36, Michal Orzel wrote:
> Hi Julien,
Hi Michal,

> On 20.04.2021 15:12, Julien Grall wrote:
> > Hi Michal,
> >
> > On 20/04/2021 08:08, Michal Orzel wrote:
> > > AArch64 system registers are 64bit whereas AArch32 ones
> > > are 32bit or 64bit. MSR/MRS are expecting 64bit values thus
> > > we should get rid of helpers READ/WRITE_SYSREG32
> > > in favour of using READ/WRITE_SYSREG.
> > > We should also use register_t type when reading sysregs
> > > which can correspond to uint64_t or uint32_t.
> > > Even though many AArch64 sysregs have upper 32bit reserved
> > > it does not mean that they can't be widen in the future.
> > >
> > > Modify type of registers: actlr, cntkctl to register_t.
> > ACTLR is implementation defined, so in theory there might already bits already 
> > defined in the range [32:63]. So I would consider to split it from the patch so 
> > we can backport it.
> You mean not to touch it at all in this series or to create a seperate patch 
> only for ACTLR?
I meant creating a separate patch for ACTLR as part of this series.


> > > Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> > > ---
> > >    xen/arch/arm/domain.c        | 20 ++++++++++----------
> > >    xen/include/asm-arm/domain.h |  4 ++--
> > >    2 files changed, 12 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> > > index bdd3d3e5b5..c021a03c61 100644
> > > --- a/xen/arch/arm/domain.c
> > > +++ b/xen/arch/arm/domain.c
> > > @@ -113,13 +113,13 @@ static void ctxt_switch_from(struct vcpu *p)
> > >        p->arch.tpidr_el1 = READ_SYSREG(TPIDR_EL1);
> > >          /* Arch timer */
> > > -    p->arch.cntkctl = READ_SYSREG32(CNTKCTL_EL1);
> > > +    p->arch.cntkctl = READ_SYSREG(CNTKCTL_EL1);
> > >        virt_timer_save(p);
> > >          if ( is_32bit_domain(p->domain) && cpu_has_thumbee )
> > >        {
> > > -        p->arch.teecr = READ_SYSREG32(TEECR32_EL1);
> > > -        p->arch.teehbr = READ_SYSREG32(TEEHBR32_EL1);
> > > +        p->arch.teecr = READ_SYSREG(TEECR32_EL1);
> > > +        p->arch.teehbr = READ_SYSREG(TEEHBR32_EL1);
> > It feels strange you converted cntkctl and actlr to use register_t but not 
> > teecr and teehbr. Can you explain why?
> Because thumbee and its registers do not appear in any of ARMv8 ARM version.
This was defined on the very first version of the ARMv8-A spec (issue 
a.a) but was dropped on subsequent versinos. Hence why the compiler 
doesn't shout at you when finding TEECR32_EL1 and TEEHBR32_EL1.
> This means that this code could be protected even with #ifdef CONFIG_ARM_32 as 
> AArch64 do not have them.
+1. The feature was completely dropped for Armv8 (even if it appeared in 
earlier version of the spec). I have checked AMD Seattle, QEMU and the 
Foundation model to confirm the feature is not exposed.
Cheers,

--
Julien Grall