Re: [PATCH v5 21/49] KVM: arm64: gic-v5: Initialise per-VM IRS state

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Unprivileged userspace can flood the kernel log (dmesg) by repeatedly triggering a `pr_warn` in `kvm_vgic_v5_irs_init()`.
--

--- Patch [21]: [PATCH v5 21/49] KVM: arm64: gic-v5: Initialise per-VM IRS state ---
commit 1471593eea3e98c7d1747cf0894424955cddde44
Author: Sascha Bischoff <[email protected]>

KVM: arm64: gic-v5: Initialise per-VM IRS state

A virtual GICv5 needs an emulated IRS in addition to the host IRS
state used to back VMTEs, VPEs, and ISTs. This patch allocates the
per-VM emulated IRS state when creating a virtual GICv5, and initialises
it from vgic_v5_init(). It also handles the teardown and cleanup of the
IRS state during VGIC destruction.

> diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
> index 2932f3cfbe8f4..6a7dabf90dd1b 100644
> --- a/arch/arm64/kvm/vgic/vgic-v5.c
> +++ b/arch/arm64/kvm/vgic/vgic-v5.c

[ ... ]

> @@ -751,6 +752,11 @@ int vgic_v5_init(struct kvm *kvm)
>  			goto err;
>  	}
>  
> +	/* Init IRS (and alloc SPI IST) */
> +	ret = kvm_vgic_v5_irs_init(kvm, kvm->arch.vgic.nr_spis);

[Severity: Medium]
Does this new call path allow userspace to flood the kernel log?

When userspace initializes a GICv5 via ioctl, this path calls
kvm_vgic_v5_irs_init(). If the host IRS hardware supports fewer than 16 ID
bits for ISTs, kvm_vgic_v5_irs_init() emits an unconditional warning:

arch/arm64/kvm/vgic/vgic-irs-v5.c:kvm_vgic_v5_irs_init() {
    ...
    if (vgic_v5_irs_ist_id_bits(&irs_caps) < 16)
        pr_warn("Host IRS supports fewer than 16 ID bits for ISTs (%u)\n",
                vgic_v5_irs_ist_id_bits(&irs_caps));
    ...
}

Since an unprivileged user can repeatedly create and destroy a VM in a tight
loop, can this be used to spam dmesg and degrade system performance? Should
this warning be converted to pr_warn_once() or be rate-limited?

> +	if (ret)
> +		goto err;
> +
>  	return 0;
>  
>  err:

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=21