linux-kernel - Re: [PATCH] iommu/vt-d: Try info->iommu in device_to

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Date:   Thu, 12 May 2022 20:59:28 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
CC:     <dwmw2@...radead.org>, <joro@...tes.org>, <will@...nel.org>,
        <jgg@...dia.com>, <iommu@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/vt-d: Try info->iommu in device_to_iommu()

On Fri, May 13, 2022 at 11:32:11AM +0800, Baolu Lu wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 2022/5/13 08:32, Nicolin Chen wrote:
> > Local boot test and VFIO sanity test show that info->iommu can be
> > used in device_to_iommu() as a fast path. So this patch adds it.
> > 
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >   drivers/iommu/intel/iommu.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 2990f80c5e08..412fca5ab9cd 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -777,6 +777,7 @@ static bool iommu_is_dummy(struct intel_iommu *iommu, struct device *dev)
> >   struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devfn)
> >   {
> >       struct dmar_drhd_unit *drhd = NULL;
> > +     struct device_domain_info *info;
> >       struct pci_dev *pdev = NULL;
> >       struct intel_iommu *iommu;
> >       struct device *tmp;
> > @@ -786,6 +787,10 @@ struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devfn)
> >       if (!dev)
> >               return NULL;
> > 
> > +     info = dev_iommu_priv_get(dev);
> > +     if (info)
> > +             return info->iommu;
> 
> device_to_iommu() also returns device source id (@bus, @devfn).
> 
> Perhaps, we can make device_to_iommu() only for probe_device() where the
> per-device info data is not initialized yet. After probe_device(), iommu
> and sid are retrieved through other helpers by looking up the device
> info directly?

That should work I think. I was just not sure when the priv
could be unset. But it seems that you have cleaned up those
places other than probe/release_device() in recent version :)

Nic