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

[Baolu Lu]

On 3/8/23 8:37 PM, Robin Murphy wrote:
> 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. 

Agreed. Perhaps, in the attach path:

	if (!dom->pgt_va)
		dom->pgt_va = dma_alloc_coherent(sdev->dev, pgt_size,
				&dom->pgt_pa, GFP_KERNEL);
?

Best regards,
baolu

> 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@xxxxxxxxxx>
> > ---
> > 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);