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Date: Sun, 17 Jan 2021 07:30:39 +0200 From: Leon Romanovsky <leon@...nel.org> To: Lu Baolu <baolu.lu@...ux.intel.com> Cc: tglx@...utronix.de, ashok.raj@...el.com, kevin.tian@...el.com, dave.jiang@...el.com, megha.dey@...el.com, dwmw2@...radead.org, alex.williamson@...hat.com, bhelgaas@...gle.com, dan.j.williams@...el.com, will@...nel.org, joro@...tes.org, dmaengine@...r.kernel.org, eric.auger@...hat.com, jacob.jun.pan@...el.com, jgg@...lanox.com, kvm@...r.kernel.org, kwankhede@...dia.com, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org, maz@...nel.org, mona.hossain@...el.com, netanelg@...lanox.com, parav@...lanox.com, pbonzini@...hat.com, rafael@...nel.org, samuel.ortiz@...el.com, sanjay.k.kumar@...el.com, shahafs@...lanox.com, tony.luck@...el.com, vkoul@...nel.org, yan.y.zhao@...ux.intel.com, yi.l.liu@...el.com Subject: Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU On Sat, Jan 16, 2021 at 04:47:40PM +0800, Lu Baolu wrote: > Hi Leon, > > On 2021/1/16 16:39, Leon Romanovsky wrote: > > On Sat, Jan 16, 2021 at 09:20:16AM +0800, Lu Baolu wrote: > > > Hi, > > > > > > On 2021/1/15 14:31, Leon Romanovsky wrote: > > > > On Fri, Jan 15, 2021 at 07:49:47AM +0800, Lu Baolu wrote: > > > > > Hi Leon, > > > > > > > > > > On 1/14/21 9:26 PM, Leon Romanovsky wrote: > > > > > > On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote: > > > > > > > Some vendor IOMMU drivers are able to declare that it is running in a VM > > > > > > > context. This is very valuable for the features that only want to be > > > > > > > supported on bare metal. Add a capability bit so that it could be used. > > > > > > > > > > > > And how is it used? Who and how will set it? > > > > > > > > > > Use the existing iommu_capable(). I should add more descriptions about > > > > > who and how to use it. > > > > > > > > I want to see the code that sets this capability. > > > > > > Currently we have Intel VT-d and the virt-iommu setting this capability. > > > > > > static bool intel_iommu_capable(enum iommu_cap cap) > > > { > > > if (cap == IOMMU_CAP_CACHE_COHERENCY) > > > return domain_update_iommu_snooping(NULL) == 1; > > > if (cap == IOMMU_CAP_INTR_REMAP) > > > return irq_remapping_enabled == 1; > > > + if (cap == IOMMU_CAP_VIOMMU) > > > + return caching_mode_enabled(); > > > > > > return false; > > > } > > > > > > And, > > > > > > +static bool viommu_capable(enum iommu_cap cap) > > > +{ > > > + if (cap == IOMMU_CAP_VIOMMU) > > > + return true; > > > + > > > + return false; > > > +} > > > > These two functions are reading this cap and not setting. > > Where can I see code that does "cap = IOMMU_CAP_VIOMMU" and not "=="? > > The iommu_capable() is a generic IOMMU interface to query IOMMU > capabilities. It takes @bus and @cap as input, and calls the callback > of vendor iommu. If the vendor iommu driver supports the specific > capability, it returns true. Otherwise, it returns false. > > bool iommu_capable(struct bus_type *bus, enum iommu_cap cap) > { > if (!bus->iommu_ops || !bus->iommu_ops->capable) > return false; > > return bus->iommu_ops->capable(cap); > } > EXPORT_SYMBOL_GPL(iommu_capable); > > In the vendor iommu's callback, it checks the capability and returns a > value according to its capability, just as showed above. Ohh, sorry. I missed "iommu_capable(dev->bus, IOMMU_CAP_VIOMMU)" from second patch. Thanks > > Best regards, > baolu
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