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Message-ID: <aab45cd3-e5ca-58cf-e081-e32a17f5b4e7@huawei.com>
Date: Tue, 22 Oct 2024 15:45:17 +0800
From: Zenghui Yu <yuzenghui@...wei.com>
To: Marc Zyngier <maz@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
Thomas Gleixner <tglx@...utronix.de>, Kunkun Jiang <jiangkunkun@...wei.com>
Subject: Re: [PATCH] irqchip/gic-v4: Don't allow a VMOVP on a dying VPE
Hi Marc,
On 2024/10/3 4:49, Marc Zyngier wrote:
> Kunkun Jiang reports that there is a small window of opportunity for
> userspace to force a change of affinity for a VPE while the VPE has
> already been unmapped, but the corresponding doorbell interrupt still
> visible in /proc/irq/.
>
> Plug the race by checking the value of vmapp_count, which tracks whether
> the VPE is mapped ot not, and returning an error in this case.
>
> This involves making vmapp_count common to both GICv4.1 and its v4.0
> ancestor.
>
> Reported-by: Kunkun Jiang <jiangkunkun@...wei.com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Link: https://lore.kernel.org/r/c182ece6-2ba0-ce4f-3404-dba7a3ab6c52@huawei.com
> ---
> drivers/irqchip/irq-gic-v3-its.c | 18 ++++++++++++------
> include/linux/irqchip/arm-gic-v4.h | 4 +++-
> 2 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index fdec478ba5e7..ab597e74ba08 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -797,8 +797,8 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
> its_encode_valid(cmd, desc->its_vmapp_cmd.valid);
>
> if (!desc->its_vmapp_cmd.valid) {
> + alloc = !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
> if (is_v4_1(its)) {
> - alloc = !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
> its_encode_alloc(cmd, alloc);
> /*
> * Unmapping a VPE is self-synchronizing on GICv4.1,
> @@ -817,13 +817,13 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
> its_encode_vpt_addr(cmd, vpt_addr);
> its_encode_vpt_size(cmd, LPI_NRBITS - 1);
>
> + alloc = !atomic_fetch_inc(&desc->its_vmapp_cmd.vpe->vmapp_count);
> +
> if (!is_v4_1(its))
> goto out;
>
> vconf_addr = virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->its_vm->vprop_page));
>
> - alloc = !atomic_fetch_inc(&desc->its_vmapp_cmd.vpe->vmapp_count);
> -
> its_encode_alloc(cmd, alloc);
>
> /*
> @@ -3806,6 +3806,13 @@ static int its_vpe_set_affinity(struct irq_data *d,
> struct cpumask *table_mask;
> unsigned long flags;
>
> + /*
> + * Check if we're racing against a VPE being destroyed, for
> + * which we don't want to allow a VMOVP.
> + */
> + if (!atomic_read(&vpe->vmapp_count))
> + return -EINVAL;
We lazily map the vPE so that vmapp_count is likely to be 0 on GICv4.0
implementations with the ITSList feature. Seems that that implementation
is not affected by the reported race and we don't need to check
vmapp_count for that.
Testing rc4 on my 920 server triggers the WARN_ON() in vgic_v3_load().
void vgic_v3_load(struct kvm_vcpu *vcpu)
{
WARN_ON(vgic_v4_load(vcpu));
Thanks,
Zenghui
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