linux-kernel - Re: [PATCH V2] iommu: sprd: release dma buffer to avoid memory leak

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Date:   Wed, 8 Mar 2023 12:37:15 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Chunyan Zhang <chunyan.zhang@...soc.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
Cc:     iommu@...ts.linux.dev, Baolu Lu <baolu.lu@...ux.intel.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] iommu: sprd: release dma buffer to avoid memory leak

On 2023-03-08 03:41, Chunyan Zhang wrote:
> Release page table DMA buffer when the IOMMU domain is not used:
> 
> - Domain freed.
> 
> - IOMMU is attaching to a new domain.
>    Since one sprd IOMMU servers only one client device, if the IOMMU has
>    been attached to other domain, it has to be detached first, that's
>    saying the DMA buffer should be released, otherwise that would
>    cause memory leak issue.

This is clearly wrong; domain resources should only be freed when the 
domain is freed. Just because a caller has detached from a domain 
doesn't mean that they can't reattach to it later and expect the 
previous mappings to still be in place - it has nothing to do with how 
many devices or domains can be active at once.

Thanks,
Robin.

> Signed-off-by: Chunyan Zhang <chunyan.zhang@...soc.com>
> ---
> V2:
> * Added some comment in sprd_iommu_attach_device() for the reason
>    of calling sprd_iommu_cleanup().
> 
> V1: https://lkml.org/lkml/2023/2/10/198
> ---
>   drivers/iommu/sprd-iommu.c | 46 ++++++++++++++++++++++++++++++++------
>   1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/sprd-iommu.c b/drivers/iommu/sprd-iommu.c
> index ae94d74b73f4..fb2f96df3bca 100644
> --- a/drivers/iommu/sprd-iommu.c
> +++ b/drivers/iommu/sprd-iommu.c
> @@ -62,6 +62,7 @@ enum sprd_iommu_version {
>    * @eb: gate clock which controls IOMMU access
>    */
>   struct sprd_iommu_device {
> +	struct sprd_iommu_domain	*dom;
>   	enum sprd_iommu_version	ver;
>   	u32			*prot_page_va;
>   	dma_addr_t		prot_page_pa;
> @@ -151,13 +152,6 @@ static struct iommu_domain *sprd_iommu_domain_alloc(unsigned int domain_type)
>   	return &dom->domain;
>   }
>   
> -static void sprd_iommu_domain_free(struct iommu_domain *domain)
> -{
> -	struct sprd_iommu_domain *dom = to_sprd_domain(domain);
> -
> -	kfree(dom);
> -}
> -
>   static void sprd_iommu_first_vpn(struct sprd_iommu_domain *dom)
>   {
>   	struct sprd_iommu_device *sdev = dom->sdev;
> @@ -230,6 +224,29 @@ static void sprd_iommu_hw_en(struct sprd_iommu_device *sdev, bool en)
>   	sprd_iommu_update_bits(sdev, reg_cfg, mask, 0, val);
>   }
>   
> +static void sprd_iommu_cleanup(struct sprd_iommu_device *sdev)
> +{
> +	struct sprd_iommu_domain *dom = sdev->dom;
> +	size_t pgt_size = sprd_iommu_pgt_size(&dom->domain);
> +
> +	dma_free_coherent(sdev->dev, pgt_size, dom->pgt_va, dom->pgt_pa);
> +	dom->sdev = NULL;
> +	sdev->dom = NULL;
> +	sprd_iommu_hw_en(sdev, false);
> +}
> +
> +static void sprd_iommu_domain_free(struct iommu_domain *domain)
> +{
> +	struct sprd_iommu_domain *dom = to_sprd_domain(domain);
> +	struct sprd_iommu_device *sdev = dom->sdev;
> +
> +	/* Free DMA buffer first if the domain has been attached */
> +	if (sdev)
> +		sprd_iommu_cleanup(sdev);
> +
> +	kfree(dom);
> +}
> +
>   static int sprd_iommu_attach_device(struct iommu_domain *domain,
>   				    struct device *dev)
>   {
> @@ -237,14 +254,29 @@ static int sprd_iommu_attach_device(struct iommu_domain *domain,
>   	struct sprd_iommu_domain *dom = to_sprd_domain(domain);
>   	size_t pgt_size = sprd_iommu_pgt_size(domain);
>   
> +	/* Return directly if the domain attached to IOMMU already */
>   	if (dom->sdev)
>   		return -EINVAL;
>   
> +	/* The IOMMU already attached to a domain */
> +	if (sdev->dom) {
> +		if (sdev->dom == dom)
> +			return 0;
> +
> +		/*
> +		 * Clean up the previous domain, one sprd IOMMU servers only
> +		 * one client device, if the IOMMU has been attached to other
> +		 * domain, it has to be detached first.
> +		 */
> +		sprd_iommu_cleanup(sdev);
> +	}
> +
>   	dom->pgt_va = dma_alloc_coherent(sdev->dev, pgt_size, &dom->pgt_pa, GFP_KERNEL);
>   	if (!dom->pgt_va)
>   		return -ENOMEM;
>   
>   	dom->sdev = sdev;
> +	sdev->dom = dom;
>   
>   	sprd_iommu_first_ppn(dom);
>   	sprd_iommu_first_vpn(dom);