Re: [Xen-devel] [PATCH v2 09/13] vtd: add lookup_page method to iommu_ops

[George Dunlap <dunlapg@xxxxxxxxx>]

On Sat, Jul 7, 2018 at 12:05 PM, Paul Durrant <paul.durrant@xxxxxxxxxx> wrote:
> This patch adds a new method to the VT-d IOMMU implementation to find the
> MFN currently mapped by the specified BFN along with a wrapper function in
> generic IOMMU code to call the implementation if it exists.
>
> This functionality will be used by a subsequent patch.
>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>
> v2:
>  - Addressed some comments from Jan.
> ---
>  xen/drivers/passthrough/iommu.c     | 11 ++++++++++
>  xen/drivers/passthrough/vtd/iommu.c | 40 
> +++++++++++++++++++++++++++++++++++++
>  xen/drivers/passthrough/vtd/iommu.h |  1 +
>  xen/include/xen/iommu.h             |  4 ++++
>  4 files changed, 56 insertions(+)
>
> diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
> index 3fbd3ebaf6..f25aa3f1d6 100644
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -306,6 +306,17 @@ int iommu_unmap_page(struct domain *d, bfn_t bfn)
>      return rc;
>  }
>
> +int iommu_lookup_page(struct domain *d, bfn_t bfn, mfn_t *mfn,
> +                      unsigned int *flags)
> +{
> +    const struct domain_iommu *hd = dom_iommu(d);
> +
> +    if ( !iommu_enabled || !hd->platform_ops )
> +        return -EOPNOTSUPP;
> +
> +    return hd->platform_ops->lookup_page(d, bfn, mfn, flags);
> +}
> +
>  static void iommu_free_pagetables(unsigned long unused)
>  {
>      do {
> diff --git a/xen/drivers/passthrough/vtd/iommu.c 
> b/xen/drivers/passthrough/vtd/iommu.c
> index 7cd3813b9f..438bef670d 100644
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1831,6 +1831,45 @@ static int __must_check intel_iommu_unmap_page(struct 
> domain *d,
>      return dma_pte_clear_one(d, bfn_to_baddr(bfn));
>  }
>
> +static int intel_iommu_lookup_page(struct domain *d, bfn_t bfn, mfn_t *mfn,
> +                                   unsigned int *flags)
> +{
> +    struct domain_iommu *hd = dom_iommu(d);
> +    struct dma_pte *page = NULL, *pte = NULL, val;
> +    u64 pg_maddr;
> +
> +    spin_lock(&hd->arch.mapping_lock);
> +
> +    pg_maddr = addr_to_dma_page_maddr(d, bfn_to_baddr(bfn), 0);
> +    if ( pg_maddr == 0 )
> +    {
> +        spin_unlock(&hd->arch.mapping_lock);
> +        return -ENOMEM;
> +    }
> +
> +    page = map_vtd_domain_page(pg_maddr);
> +    pte = page + (bfn_x(bfn) & LEVEL_MASK);
> +    val = *pte;
> +    if ( !dma_pte_present(val) )
> +    {
> +        unmap_vtd_domain_page(page);
> +        spin_unlock(&hd->arch.mapping_lock);
> +        return -ENOMEM;

Should this be -EEXIST?  Or maybe return MFN_INVALID?

Also, could you do the unmap / unlock first and then do the check,
rather than duplicating things?

> +    }
> +
> +    unmap_vtd_domain_page(page);
> +    spin_unlock(&hd->arch.mapping_lock);
> +
> +    *mfn = maddr_to_mfn(dma_pte_addr(val));
> +    *flags = 0;
> +    if ( dma_pte_prot(val) & DMA_PTE_READ )
> +        *flags |= IOMMUF_readable;
> +    if ( dma_pte_prot(val) & DMA_PTE_WRITE )
> +        *flags |= IOMMUF_writable;

This is a bit strange, since all dma_pte_prot() does is return val &
DMA_PTE_READ|DMA_PTE_WRITE.  Would it make sense to implement
dma_pte_read() / dma_pte_write() instead (like dma_pte_present())?

Everything else looks good to me.

 -George

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