Re: [PATCH 5/9] arm/mm: Get rid of READ/WRITE_SYSREG32

[Julien Grall <julien@xxxxxxx>]

On 22/04/2021 12:47, Michal Orzel wrote:
> Hi Julien,
Hi Michal,

> On 20.04.2021 15:37, 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 SCTLR_EL2 accesses to use READ/WRITE_SYSREG.
> > SCTLR_EL2 already has bits defined in the range [32:63]. So this change is 
> > going to have a side effect as AFAICT head.S will not touch those bits. So they 
> > are now going to be preserved.
> >
> > The Arm Arm defines them as unknown if implemented. Therefore shouldn't we zero 
> > them somewhere else?
> SCTLR_EL2 is set in head.S using SCTLR_EL2_SET which means that we are zeroing 
> the upper 32bit half.
Ah! I couldn't find the place doing it. Thanks!

I think it is important to point in the commit message this is just a 
latent bug because the top 32-bit was not used by Xen. Can you update 
the commit message?
Cheers,

--
Julien Grall