linux-kernel - Re: [PATCH v2 2/2] vfio/iommu_type1: Sanity check pfn_list when remove vfio

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Message-ID: <20210115121447.54c96857@omen.home.shazbot.org>
Date:   Fri, 15 Jan 2021 12:14:47 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH v2 2/2] vfio/iommu_type1: Sanity check pfn_list when
 remove vfio_dma

On Fri, 15 Jan 2021 17:26:43 +0800
Keqian Zhu <zhukeqian1@...wei.com> wrote:

> vfio_sanity_check_pfn_list() is used to check whether pfn_list of
> vfio_dma is empty when remove the external domain, so it makes a
> wrong assumption that only external domain will add pfn to dma pfn_list.
> 
> Now we apply this check when remove a specific vfio_dma and extract
> the notifier check just for external domain.

The page pinning interface is gated by having a notifier registered for
unmaps, therefore non-external domains would also need to register a
notifier.  There's currently no other way to add entries to the
pfn_list.  So if we allow pinning for such domains, then it's wrong to
WARN_ON() when the notifier list is not-empty when removing an external
domain.  Long term we should probably extend page {un}pinning for the
caller to pass their notifier to be validated against the notifier list
rather than just allowing page pinning if *any* notifier is registered.
Thanks,

Alex
 
> Fixes: a54eb55045ae ("vfio iommu type1: Add support for mediated devices")
> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 24 +++++-------------------
>  1 file changed, 5 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 4e82b9a3440f..a9bc15e84a4e 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -958,6 +958,7 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
>  
>  static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  {
> +	WARN_ON(!RB_EMPTY_ROOT(&dma->pfn_list);
>  	vfio_unmap_unpin(iommu, dma, true);
>  	vfio_unlink_dma(iommu, dma);
>  	put_task_struct(dma->task);
> @@ -2251,23 +2252,6 @@ static void vfio_iommu_unmap_unpin_reaccount(struct vfio_iommu *iommu)
>  	}
>  }
>  
> -static void vfio_sanity_check_pfn_list(struct vfio_iommu *iommu)
> -{
> -	struct rb_node *n;
> -
> -	n = rb_first(&iommu->dma_list);
> -	for (; n; n = rb_next(n)) {
> -		struct vfio_dma *dma;
> -
> -		dma = rb_entry(n, struct vfio_dma, node);
> -
> -		if (WARN_ON(!RB_EMPTY_ROOT(&dma->pfn_list)))
> -			break;
> -	}
> -	/* mdev vendor driver must unregister notifier */
> -	WARN_ON(iommu->notifier.head);
> -}
> -
>  /*
>   * Called when a domain is removed in detach. It is possible that
>   * the removed domain decided the iova aperture window. Modify the
> @@ -2367,7 +2351,8 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>  			kfree(group);
>  
>  			if (list_empty(&iommu->external_domain->group_list)) {
> -				vfio_sanity_check_pfn_list(iommu);
> +				/* mdev vendor driver must unregister notifier */
> +				WARN_ON(iommu->notifier.head);
>  
>  				if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
>  					vfio_iommu_unmap_unpin_all(iommu);
> @@ -2491,7 +2476,8 @@ static void vfio_iommu_type1_release(void *iommu_data)
>  
>  	if (iommu->external_domain) {
>  		vfio_release_domain(iommu->external_domain, true);
> -		vfio_sanity_check_pfn_list(iommu);
> +		/* mdev vendor driver must unregister notifier */
> +		WARN_ON(iommu->notifier.head);
>  		kfree(iommu->external_domain);
>  	}
>