linux-kernel - Re: [PATCH 4/5] vfio/iommu_type1: Carefully use unmap_unpin

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Date:   Mon, 11 Jan 2021 14:49:13 -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 4/5] vfio/iommu_type1: Carefully use unmap_unpin_all
 during dirty tracking

On Thu, 7 Jan 2021 17:29:00 +0800
Keqian Zhu <zhukeqian1@...wei.com> wrote:

> If we detach group during dirty page tracking, we shouldn't remove
> vfio_dma, because dirty log will lose.
> 
> But we don't prevent unmap_unpin_all in vfio_iommu_release, because
> under normal procedure, dirty tracking has been stopped.

This looks like it's creating a larger problem than it's fixing, it's
not our job to maintain the dirty bitmap regardless of what the user
does.  If the user detaches the last group in a container causing the
mappings within that container to be deconstructed before the user has
collected dirty pages, that sounds like a user error.  A container with
no groups is de-privileged and therefore loses all state.  Thanks,

Alex

> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 26b7eb2a5cfc..9776a059904d 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2373,7 +2373,12 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>  			if (list_empty(&iommu->external_domain->group_list)) {
>  				vfio_sanity_check_pfn_list(iommu);
>  
> -				if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
> +				/*
> +				 * During dirty page tracking, we can't remove
> +				 * vfio_dma because dirty log will lose.
> +				 */
> +				if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) &&
> +				    !iommu->dirty_page_tracking)
>  					vfio_iommu_unmap_unpin_all(iommu);
>  
>  				kfree(iommu->external_domain);
> @@ -2406,10 +2411,15 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>  		 * iommu and external domain doesn't exist, then all the
>  		 * mappings go away too. If it's the last domain with iommu and
>  		 * external domain exist, update accounting
> +		 *
> +		 * Note: During dirty page tracking, we can't remove vfio_dma
> +		 * because dirty log will lose. Just update accounting is a good
> +		 * choice.
>  		 */
>  		if (list_empty(&domain->group_list)) {
>  			if (list_is_singular(&iommu->domain_list)) {
> -				if (!iommu->external_domain)
> +				if (!iommu->external_domain &&
> +				    !iommu->dirty_page_tracking)
>  					vfio_iommu_unmap_unpin_all(iommu);
>  				else
>  					vfio_iommu_unmap_unpin_reaccount(iommu);