Re: [PATCH 1/3] KVM: arm64: timers: Fix percpu address space issues in kvm_timer_hyp_init()

Uros Bizjak
2025-01-16T14:25:22Z

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On Fri, Dec 13, 2024 at 6:15 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On Fri, 13 Dec 2024 14:57:52 +0000,
> Uros Bizjak <ubizjak@gmail.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@gmail.com>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Oliver Upton <oliver.upton@linux.dev>
> > Cc: Joey Gouly <joey.gouly@arm.com>
> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Cc: Zenghui Yu <yuzenghui@huawei.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will@kernel.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.

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diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 1215df590418..10c293c2d2f5 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -1238,12 +1238,10 @@ void kvm_arm_timer_write_sysreg(struct kvm_vcpu *vcpu,
}
}

-static int timer_irq_set_vcpu_affinity(struct irq_data *d, void *vcpu)
+static int timer_irq_set_vcpu_affinity(struct irq_data *d,
+ void __always_unused *vcpu)
{
- if (vcpu)
- irqd_set_forwarded_to_vcpu(d);
- else
- irqd_clr_forwarded_to_vcpu(d);
+ irqd_set_forwarded_to_vcpu(d);

return 0;
}
@@ -1391,8 +1389,7 @@ 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, NULL);
if (err) {
kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
goto out_free_vtimer_irq;
@@ -1415,8 +1412,7 @@ 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, NULL);
if (err) {
kvm_err("kvm_arch_timer: error setting vcpu affinity\n");
goto out_free_ptimer_irq;