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

Marc Zyngier
2024-12-13T17:15:30Z

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.

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.