Re: [Xen-devel] FIXME question

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Xu, Quan
> Sent: Monday, June 27, 2016 5:24 PM
> To: xen-devel@xxxxxxxxxxxxx
> Cc: Jan Beulich <JBeulich@xxxxxxxx>; Tian, Kevin <kevin.tian@xxxxxxxxx>; Wu,
> Feng <feng.wu@xxxxxxxxx>
> Subject: FIXME question
> 
> Hi,
> 
> When I read IOMMU code,
> In xen/drivers/passthrough/vtd/intremap.c : pi_update_irte()..
> There are a FIXME --
> ''
> * FIXME: For performance reasons we should store the 'iommu' pointer in
> * 'struct msi_desc' in some other place, so we don't need to waste
> * time searching it here.
> "
> 
> IMO, we are better to store the 'iommu' pointer in pci_dev, then
> could I fix it as:

Yes, I think saving the 'iommu' pointer in pci_dev is the right direction.

Thanks,
Feng

> 
> 1. save a void *iommu  in pci_dev structure:
> 
> --- a/xen/include/xen/pci.h
> +++ b/xen/include/xen/pci.h
> @@ -83,6 +83,8 @@ struct pci_dev {
>  #define PT_FAULT_THRESHOLD 10
>      } fault;
>      u64 vf_rlen[6];
> +
> +   void *iommu; /* No common IOMMU struct so use void pointer */
>  };
> 
> 
> 
> 2. Save iommu pointer in 'struct pci_dev' when to add device:
> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1994,6 +1994,7 @@ static int intel_iommu_enable_device(struct pci_dev
> *pdev)
>      if ( ret <= 0 )
>          return ret;
> 
> +    pdev->iommu = drhd->iommu;
>      ret = enable_ats_device(pdev->seg, pdev->bus, pdev->devfn, drhd->iommu);
> 
> 3. use iommu pointer from pci_dev instead of calling
> acpi_find_matched_drhd_unit each time (also fix the related code).
> 
> 
> -Quan
> 

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