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

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Message-ID: <86bjxfsdw0.wl-maz@kernel.org>
Date: Fri, 13 Dec 2024 17:15:27 +0000
From: Marc Zyngier <maz@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
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, 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.

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.