linux-kernel - Re: [PATCH 1/3] KVM: arm64: timers: Fix percpu address space issues in kvm_timer_hyp

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Message-ID: <CAFULd4Zf4=bh6X+xg+0i5jE8doyD_ffpaWOhsdHciVHRrQj+9A@mail.gmail.com>
Date: Thu, 16 Jan 2025 15:25:09 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Oliver Upton <oliver.upton@...ux.dev>, 
	Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Zenghui Yu <yuzenghui@...wei.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/3] KVM: arm64: timers: Fix percpu address space issues
 in kvm_timer_hyp_init()

On Fri, Dec 13, 2024 at 6:15 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Fri, 13 Dec 2024 14:57:52 +0000,
> Uros Bizjak <ubizjak@...il.com> wrote:
> >
> > Cast return value from kvm_get_running_vcpus() in the __percpu
> > address space to the generic address space via uintptr_t [1]
> > to fix a couple of:
> >
> > arch_timer.c:1395:66: warning: incorrect type in argument 2 (different address spaces)
> > arch_timer.c:1395:66:    expected void *vcpu_info
> > arch_timer.c:1395:66:    got struct kvm_vcpu *[noderef] __percpu *
> >
> > sparse warnings.
> >
> > There were no changes in the resulting object files.
> >
> > [1] https://sparse.docs.kernel.org/en/latest/annotations.html#address-space-name
> >
> > Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> > Cc: Marc Zyngier <maz@...nel.org>
> > Cc: Oliver Upton <oliver.upton@...ux.dev>
> > Cc: Joey Gouly <joey.gouly@....com>
> > Cc: Suzuki K Poulose <suzuki.poulose@....com>
> > Cc: Zenghui Yu <yuzenghui@...wei.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will@...nel.org>
> > ---
> >  arch/arm64/kvm/arch_timer.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> > index 1215df590418..a13bb9e8dc19 100644
> > --- a/arch/arm64/kvm/arch_timer.c
> > +++ b/arch/arm64/kvm/arch_timer.c
> > @@ -1392,7 +1392,7 @@ int __init kvm_timer_hyp_init(bool has_gic)
> >
> >       if (has_gic) {
> >               err = irq_set_vcpu_affinity(host_vtimer_irq,
> > -                                         kvm_get_running_vcpus());
> > +                                         (void *)(uintptr_t)kvm_get_running_vcpus());
> >               if (err) {
> >                       kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
> >                       goto out_free_vtimer_irq;
> > @@ -1416,7 +1416,7 @@ int __init kvm_timer_hyp_init(bool has_gic)
> >
> >               if (has_gic) {
> >                       err = irq_set_vcpu_affinity(host_ptimer_irq,
> > -                                                 kvm_get_running_vcpus());
> > +                                                 (void *)(uintptr_t)kvm_get_running_vcpus());
> >                       if (err) {
> >                               kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
> >                               goto out_free_ptimer_irq;
>
> I think the fix is worse than the current code, because there is no
> real semantics behind the pointer being passed to
> irq_set_vcpu_affinity(). All that is required is that it is a non-NULL
> pointer.

If this is the case, we can just remove dependence on the pointer in
the called function.

Something like in the attached patch.

Uros.

> I expect the following hack to work just as well and not suffer from
> any sparse indigestion. Untested though.
>
>         M.
>
> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> index 1215df5904185..8058d92048fb4 100644
> --- a/arch/arm64/kvm/arch_timer.c
> +++ b/arch/arm64/kvm/arch_timer.c
> @@ -1391,8 +1391,7 @@ int __init kvm_timer_hyp_init(bool has_gic)
>         }
>
>         if (has_gic) {
> -               err = irq_set_vcpu_affinity(host_vtimer_irq,
> -                                           kvm_get_running_vcpus());
> +               err = irq_set_vcpu_affinity(host_vtimer_irq, info);
>                 if (err) {
>                         kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
>                         goto out_free_vtimer_irq;
> @@ -1415,8 +1414,7 @@ int __init kvm_timer_hyp_init(bool has_gic)
>                 }
>
>                 if (has_gic) {
> -                       err = irq_set_vcpu_affinity(host_ptimer_irq,
> -                                                   kvm_get_running_vcpus());
> +                       err = irq_set_vcpu_affinity(host_ptimer_irq, info);
>                         if (err) {
>                                 kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
>                                 goto out_free_ptimer_irq;
>
> --
> Without deviation from the norm, progress is not possible.

View attachment "arch_timer.diff.txt" of type "text/plain" (1255 bytes)