On Wed, Aug 18, 2021 at 02:34:03PM -0700, Oliver Upton wrote:

Hi Ricardo,

On Wed, Aug 18, 2021 at 2:32 PM Ricardo Koller [off-list ref] wrote:

quoted

vgic_get_irq(intid) is used all over the vgic code in order to get a
reference to a struct irq. It warns whenever intid is not a valid number
(like when it's a reserved IRQ number). The issue is that this warning
can be triggered from userspace (e.g., KVM_IRQ_LINE for intid 1020).

Drop the WARN call from vgic_get_irq.

Signed-off-by: Ricardo Koller <redacted>
---
 arch/arm64/kvm/vgic/vgic.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 111bff47e471..81cec508d413 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c

@@ -106,7 +106,6 @@ struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
        if (intid >= VGIC_MIN_LPI)
                return vgic_get_lpi(kvm, intid);

-       WARN(1, "Looking up struct vgic_irq for reserved INTID");

Could we maybe downgrade the message to WARN_ONCE() (to get a stack)
or pr_warn_ratelimited()? I agree it is problematic that userspace can
cause this WARN to fire, but it'd be helpful for debugging too.

Was thinking about that, until I found this in bug.h:

	/*
	 * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
	 * significant kernel issues that need prompt attention if they should ever
	 * appear at runtime.
	 *
	 * Do not use these macros when checking for invalid external inputs
	 * (e.g. invalid system call arguments, or invalid data coming from
	 * network/devices),

Just in case, KVM_IRQ_LINE returns -EINVAL for an invalid intid (like
1020). I think it's more appropriate for the vmm to log it. What do you
think?

Thanks,
Ricardo

--
Thanks,
Oliver

quoted

        return NULL;
 }

--
2.33.0.rc2.250.ged5fa647cd-goog