linux-kernel - Re: [PATCH v7 1/7] PCI/ATS: Fix pci_prg_resp_pasid

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Message-ID: <20191003203726.GA14637@skuppusw-desk.amr.corp.intel.com>
Date:   Thu, 3 Oct 2019 13:37:26 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com, keith.busch@...el.com
Subject: Re: [PATCH v7 1/7] PCI/ATS: Fix pci_prg_resp_pasid_required()
 dependency issues

On Thu, Oct 03, 2019 at 02:04:13PM -0500, Bjorn Helgaas wrote:
> On Thu, Oct 03, 2019 at 10:20:24AM -0700, Kuppuswamy Sathyanarayanan wrote:
> > Hi Bjorn,
> > 
> > Thanks for looking into this patch set.
> > 
> > On 9/5/19 12:18 PM, Bjorn Helgaas wrote:
> > > On Wed, Aug 28, 2019 at 03:14:01PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > > 
> > > > Since pci_prg_resp_pasid_required() function has dependency on both
> > > > PASID and PRI, define it only if both CONFIG_PCI_PRI and
> > > > CONFIG_PCI_PASID config options are enabled.
> > > > 
> > > > Fixes: e5567f5f6762 ("PCI/ATS: Add pci_prg_resp_pasid_required()
> > > > interface.")
> > > [Don't split tags, including "Fixes:" across lines]
> > > 
> > > This definitely doesn't fix e5567f5f6762.  That commit added
> > > pci_prg_resp_pasid_required(), but with no dependency on
> > > CONFIG_PCI_PRI or CONFIG_PCI_PASID.
> > > 
> > > This patch is only required when a subsequent patch is applied.  It
> > > should be squashed into the commit that requires it so it's obvious
> > > why it's needed.
> > > 
> > > I've been poking at this series, and I'll post a v8 soon with this and
> > > other fixes.
> > In your v8 submission you did not merge this patch. You did not use
> > pri_cap or pasid_cap cached values. Instead you have re-read the
> > value from register. Is this intentional?
> > 
> > Since this function will be called for every VF device we might loose some
> > performance benefit.
> 
> This particular patch doesn't do any caching.  IIRC it fiddles with
> ifdefs to solve a problem that would be introduced by a future patch.
> I don't remember the exact details, but I think the series I merged
> doesn't have that problem.  If it does, let me know the details and we
> can fix it.
This patch by itself does not do any caching. But your caching patch
missed modifying this function to use cached values. Please check the
current implementation of this function. It still reads
PCI_EXT_CAP_ID_PRI register instead of using cached value. Please let
me know your comments.

int pci_prg_resp_pasid_required(struct pci_dev *pdev)
{
    u16 status;
    int pri;

    if (pdev->is_virtfn)
        pdev = pci_physfn(pdev);

    pri = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
    if (!pri)
        return 0;

    pci_read_config_word(pdev, pri + PCI_PRI_STATUS, &status);

    if (status & PCI_PRI_STATUS_PASID)
        return 1;

    return 0;
}
EXPORT_SYMBOL_GPL(pci_prg_resp_pasid_required);

If caching is applied to this function then we need this #ifdef
dependency correction patch.

> 
> I did include the caching patches for both PRI and PASID capabilities,
> but they're only performance optimizations so I moved them to the end
> so the functional fixes would be smaller and earlier in the series.
> 
> > > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > > > ---
> > > >   drivers/pci/ats.c       | 10 ++++++----
> > > >   include/linux/pci-ats.h | 12 +++++++++---
> > > >   2 files changed, 15 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> > > > index e18499243f84..cdd936d10f68 100644
> > > > --- a/drivers/pci/ats.c
> > > > +++ b/drivers/pci/ats.c
> > > > @@ -395,6 +395,8 @@ int pci_pasid_features(struct pci_dev *pdev)
> > > >   }
> > > >   EXPORT_SYMBOL_GPL(pci_pasid_features);
> > > > +#ifdef CONFIG_PCI_PRI
> > > > +
> > > >   /**
> > > >    * pci_prg_resp_pasid_required - Return PRG Response PASID Required bit
> > > >    *				 status.
> > > > @@ -402,10 +404,8 @@ EXPORT_SYMBOL_GPL(pci_pasid_features);
> > > >    *
> > > >    * Returns 1 if PASID is required in PRG Response Message, 0 otherwise.
> > > >    *
> > > > - * Even though the PRG response PASID status is read from PRI Status
> > > > - * Register, since this API will mainly be used by PASID users, this
> > > > - * function is defined within #ifdef CONFIG_PCI_PASID instead of
> > > > - * CONFIG_PCI_PRI.
> > > > + * Since this API has dependency on both PRI and PASID, protect it
> > > > + * with both CONFIG_PCI_PRI and CONFIG_PCI_PASID.
> > > >    */
> > > >   int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > > >   {
> > > > @@ -425,6 +425,8 @@ int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > > >   }
> > > >   EXPORT_SYMBOL_GPL(pci_prg_resp_pasid_required);
> > > > +#endif
> > > > +
> > > >   #define PASID_NUMBER_SHIFT	8
> > > >   #define PASID_NUMBER_MASK	(0x1f << PASID_NUMBER_SHIFT)
> > > >   /**
> > > > diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h
> > > > index 1ebb88e7c184..1a0bdaee2f32 100644
> > > > --- a/include/linux/pci-ats.h
> > > > +++ b/include/linux/pci-ats.h
> > > > @@ -40,7 +40,6 @@ void pci_disable_pasid(struct pci_dev *pdev);
> > > >   void pci_restore_pasid_state(struct pci_dev *pdev);
> > > >   int pci_pasid_features(struct pci_dev *pdev);
> > > >   int pci_max_pasids(struct pci_dev *pdev);
> > > > -int pci_prg_resp_pasid_required(struct pci_dev *pdev);
> > > >   #else  /* CONFIG_PCI_PASID */
> > > > @@ -67,11 +66,18 @@ static inline int pci_max_pasids(struct pci_dev *pdev)
> > > >   	return -EINVAL;
> > > >   }
> > > > +#endif /* CONFIG_PCI_PASID */
> > > > +
> > > > +#if defined(CONFIG_PCI_PRI) && defined(CONFIG_PCI_PASID)
> > > > +
> > > > +int pci_prg_resp_pasid_required(struct pci_dev *pdev);
> > > > +
> > > > +#else /* CONFIG_PCI_PASID && CONFIG_PCI_PRI */
> > > > +
> > > >   static inline int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> > > >   {
> > > >   	return 0;
> > > >   }
> > > > -#endif /* CONFIG_PCI_PASID */
> > > > -
> > > > +#endif
> > > >   #endif /* LINUX_PCI_ATS_H*/
> > > > -- 
> > > > 2.21.0
> > > > 
> > -- 
> > Sathyanarayanan Kuppuswamy
> > Linux kernel developer
> > 

-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer