RE: [PATCH v3 3/3] arm64: paravirt: Enable errata based on implementation CPUs

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Cornelia Huck <cohuck@redhat.com>
> Sent: Monday, December 9, 2024 12:49 PM
> To: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@huawei.com>; kvmarm@lists.linux.dev;
> maz@kernel.org; oliver.upton@linux.dev
> Cc: catalin.marinas@arm.com; will@kernel.org; mark.rutland@arm.com;
> eric.auger@redhat.com; yuzenghui <yuzenghui@huawei.com>; Wangzhou
> (B) <wangzhou1@hisilicon.com>; jiangkunkun <jiangkunkun@huawei.com>;
> Jonathan Cameron <jonathan.cameron@huawei.com>; Anthony Jebson
> <anthony.jebson@huawei.com>; linux-arm-kernel@lists.infradead.org;
> Linuxarm <linuxarm@huawei.com>
> Subject: Re: [PATCH v3 3/3] arm64: paravirt: Enable errata based on
> implementation CPUs
> 
> On Mon, Dec 09 2024, Shameer Kolothum
> <shameerali.kolothum.thodi@huawei.com> wrote:
> 
> > Retrieve any migration target implementation CPUs using the hypercall
> > and enable associated errata.
> >
> > Signed-off-by: Shameer Kolothum
> <shameerali.kolothum.thodi@huawei.com>
> > ---
> > Note:
> >
> > One thing I am not sure here is how to handle the hypercall error.
> > Do we need to fail the Guest boot or just carry on without any
> > target implementation CPU support? At the moment it just carries on.
> >
> > Thanks,
> > Shameer
> > ---
> >  arch/arm64/include/asm/cputype.h  | 25 +++++++++++++++++++++++--
> >  arch/arm64/include/asm/paravirt.h |  3 +++
> >  arch/arm64/kernel/cpu_errata.c    | 20 +++++++++++++++++---
> >  arch/arm64/kernel/cpufeature.c    |  2 ++
> >  arch/arm64/kernel/image-vars.h    |  2 ++
> >  arch/arm64/kernel/paravirt.c      | 31
> +++++++++++++++++++++++++++++++
> >  6 files changed, 78 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/cputype.h
> b/arch/arm64/include/asm/cputype.h
> > index dcf0e1ce892d..9e466f3ae9c6 100644
> > --- a/arch/arm64/include/asm/cputype.h
> > +++ b/arch/arm64/include/asm/cputype.h
> > @@ -265,6 +265,16 @@ struct midr_range {
> >  #define MIDR_REV(m, v, r) MIDR_RANGE(m, v, r, v, r)
> >  #define MIDR_ALL_VERSIONS(m) MIDR_RANGE(m, 0, 0, 0xf, 0xf)
> >
> > +#define MAX_TARGET_IMPL_CPUS 64
> > +
> > +struct target_impl_cpu {
> > +	u32 midr;
> > +	u32 revidr;
> > +};
> 
> Doesn't this need to be u64 for both (even if the upper bits for
> MIDR_EL1 are reserved?)

Yes, both are u64 as per specification with upper bits reserved. And the 
external hypercall interface has uint64.

But in kernel, AFAICS, at present all the _midr_range_() functions expect u32.
So not sure we gain much now by changing to u64.

Thanks,
Shameer