linux-kernel - Re: [PATCH v4 14/22] iommu/vt-d: Add custom allocator for IOASID

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Date:   Mon, 5 Aug 2019 13:02:04 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 14/22] iommu/vt-d: Add custom allocator for IOASID

On Tue, 16 Jul 2019 11:30:14 +0200
Auger Eric <eric.auger@...hat.com> wrote:

> Hi Jacob,
> 
> On 6/9/19 3:44 PM, Jacob Pan wrote:
> > When VT-d driver runs in the guest, PASID allocation must be
> > performed via virtual command interface. This patch registers a
> > custom IOASID allocator which takes precedence over the default
> > XArray based allocator. The resulting IOASID allocation will always
> > come from the host. This ensures that PASID namespace is system-
> > wide.
> > 
> > Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> > Signed-off-by: Liu, Yi L <yi.l.liu@...el.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > ---
> >  drivers/iommu/Kconfig       |  1 +
> >  drivers/iommu/intel-iommu.c | 60
> > +++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/intel-iommu.h |  2 ++ 3 files changed, 63
> > insertions(+)
> > 
> > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > index c40c4b5..5d1bc2a 100644
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -213,6 +213,7 @@ config INTEL_IOMMU_SVM
> >  	bool "Support for Shared Virtual Memory with Intel IOMMU"
> >  	depends on INTEL_IOMMU && X86
> >  	select PCI_PASID
> > +	select IOASID
> >  	select MMU_NOTIFIER
> >  	select IOASID
> >  	help
> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 09b8ff0..5b84994 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -1711,6 +1711,8 @@ static void free_dmar_iommu(struct
> > intel_iommu *iommu) if (ecap_prs(iommu->ecap))
> >  			intel_svm_finish_prq(iommu);
> >  	}
> > +	ioasid_unregister_allocator(&iommu->pasid_allocator);
> > +
> >  #endif
> >  }
> >  
> > @@ -4820,6 +4822,46 @@ static int __init
> > platform_optin_force_iommu(void) return 1;
> >  }
> >  
> > +#ifdef CONFIG_INTEL_IOMMU_SVM
> > +static ioasid_t intel_ioasid_alloc(ioasid_t min, ioasid_t max,
> > void *data) +{
> > +	struct intel_iommu *iommu = data;
> > +	ioasid_t ioasid;
> > +
> > +	/*
> > +	 * VT-d virtual command interface always uses the full 20
> > bit
> > +	 * PASID range. Host can partition guest PASID range based
> > on
> > +	 * policies but it is out of guest's control.
> > +	 */
> > +	if (min < PASID_MIN || max > PASID_MAX)
> > +		return -EINVAL;  
> ioasid_alloc() does not handle that error value, use INVALID_IOASID?
> > +
> > +	if (vcmd_alloc_pasid(iommu, &ioasid))
> > +		return INVALID_IOASID;
> > +
> > +	return ioasid;
> > +}
> > +
> > +static void intel_ioasid_free(ioasid_t ioasid, void *data)
> > +{
> > +	struct iommu_pasid_alloc_info *svm;
> > +	struct intel_iommu *iommu = data;
> > +
> > +	if (!iommu)
> > +		return;
> > +	/*
> > +	 * Sanity check the ioasid owner is done at upper layer,
> > e.g. VFIO
> > +	 * We can only free the PASID when all the devices are
> > unbond.
> > +	 */
> > +	svm = ioasid_find(NULL, ioasid, NULL);
> > +	if (!svm) {
> > +		pr_warn("Freeing unbond IOASID %d\n", ioasid);
> > +		return;
> > +	}
> > +	vcmd_free_pasid(iommu, ioasid);
> > +}
> > +#endif
> > +
> >  int __init intel_iommu_init(void)
> >  {
> >  	int ret = -ENODEV;
> > @@ -4924,6 +4966,24 @@ int __init intel_iommu_init(void)
> >  				       "%s", iommu->name);
> >  		iommu_device_set_ops(&iommu->iommu,
> > &intel_iommu_ops); iommu_device_register(&iommu->iommu);
> > +#ifdef CONFIG_INTEL_IOMMU_SVM
> > +		if (cap_caching_mode(iommu->cap) &&
> > sm_supported(iommu)) {
> > +			/*
> > +			 * Register a custom ASID allocator if we
> > are running
> > +			 * in a guest, the purpose is to have a
> > system wide PASID
> > +			 * namespace among all PASID users.
> > +			 * There can be multiple vIOMMUs in each
> > guest but only
> > +			 * one allocator is active. All vIOMMU
> > allocators will
> > +			 * eventually be calling the same host
> > allocator.
> > +			 */
> > +			iommu->pasid_allocator.alloc =
> > intel_ioasid_alloc;
> > +			iommu->pasid_allocator.free =
> > intel_ioasid_free;
> > +			iommu->pasid_allocator.pdata = (void
> > *)iommu;
> > +			ret =
> > ioasid_register_allocator(&iommu->pasid_allocator);
> > +			if (ret)
> > +				pr_warn("Custom PASID allocator
> > registeration failed\n");  
> what if it fails, don't you want a tear down path?
> 

Good point, we need to disable PASID usage, i.e. disable scalable mode
if there is no virtual command based PASID allocator in the guest.

Sorry for the late reply.

> Thanks
> 
> Eric
>  [...]  

[Jacob Pan]