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From: "Liu, Yi L" <yi.l.liu@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"mst@redhat.com" <mst@redhat.com>,
	"eric.auger@redhat.com" <eric.auger@redhat.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	"Tian, Jun J" <jun.j.tian@intel.com>,
	"Sun, Yi Y" <yi.y.sun@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Wu, Hao" <hao.wu@intel.com>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>,
	Yi Sun <yi.y.sun@linux.intel.com>,
	Richard Henderson <rth@twiddle.net>,
	"Eduardo Habkost" <ehabkost@redhat.com>
Subject: RE: [RFC v3 14/25] intel_iommu: add virtual command capability support
Date: Sat, 15 Feb 2020 08:49:02 +0000
Message-ID: <A2975661238FB949B60364EF0F2C25743A1BE85D@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <20200213150853.GB1103216@xz-x1>

> From: Peter Xu < peterx@redhat.com >
> Sent: Thursday, February 13, 2020 11:09 PM
> To: Liu, Yi L <yi.l.liu@intel.com>
> Subject: Re: [RFC v3 14/25] intel_iommu: add virtual command capability support
> 
> On Thu, Feb 13, 2020 at 09:31:10AM -0500, Peter Xu wrote:
> 
> [...]
> 
> > > > Apart of this: also I just noticed (when reading the latter part of
> > > > the series) that the time that a pasid table walk can consume will
> > > > depend on this value too.  I'd suggest to make this as small as we
> > > > can, as long as it satisfies the usage.  We can even bump it in the
> > > > future.
> > >
> > > I see. This looks to be an optimization. right? Instead of modify the
> > > value of this macro,  I think we can do this optimization by tracking
> > > the allocated PASIDs in QEMU. Thus, the pasid table walk  would be more
> > > efficient and also no dependency on the VTD_MAX_HPASID. Does it make
> > > sense to you? :-)
> >
> > Yeah sounds good. :)
> 
> Just to make sure it's safe even for when the global allocation is not
> happening (full emulation devices?  Do they need the PASID table walk
> too?). 

I'd say no. For full emulation devices, just needs to ensure the pasid cache
is latest (do what guest told). Even the invalidation flushes too much cache,
it just affects the performance but no correctness issue.  This is different
with passthru devices, if unbind too much, it means some passthru devices
may encounter DMA  fault later.

> Anyway, be careful to not miss some valid PASID entries, or we
> can still use the MIN(PASID_MAX, CONTEXT_ENTRY_SIZE) to be safe as a
> first version.  Thanks,

Agreed. First version to ensure 100% safe.

Regards,
Yi Liu

  reply index

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-29 12:16 [RFC v3 00/25] intel_iommu: expose Shared Virtual Addressing to VMs Liu, Yi L
2020-01-29 12:16 ` [RFC v3 01/25] hw/pci: modify pci_setup_iommu() to set PCIIOMMUOps Liu, Yi L
2020-01-29 12:16 ` [RFC v3 02/25] hw/iommu: introduce DualStageIOMMUObject Liu, Yi L
2020-01-31  3:59   ` David Gibson
2020-01-31 11:42     ` Liu, Yi L
2020-02-12  6:32       ` David Gibson
2020-01-29 12:16 ` [RFC v3 03/25] hw/iommu: introduce IOMMUContext Liu, Yi L
2020-01-31  4:06   ` David Gibson
2020-01-31 11:42     ` Liu, Yi L
2020-02-11 16:58       ` Peter Xu
2020-02-12  7:15         ` Liu, Yi L
2020-02-12 15:59           ` Peter Xu
2020-02-13  2:46             ` Liu, Yi L
2020-02-14  5:36           ` David Gibson
2020-02-15  6:25             ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 04/25] hw/pci: introduce pci_device_iommu_context() Liu, Yi L
2020-01-29 12:16 ` [RFC v3 05/25] intel_iommu: provide get_iommu_context() callback Liu, Yi L
2020-01-29 12:16 ` [RFC v3 06/25] scripts/update-linux-headers: Import iommu.h Liu, Yi L
2020-01-29 12:25   ` Cornelia Huck
2020-01-31 11:40     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 07/25] header file update VFIO/IOMMU vSVA APIs Liu, Yi L
2020-01-29 12:28   ` Cornelia Huck
2020-01-31 11:41     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 08/25] vfio: pass IOMMUContext into vfio_get_group() Liu, Yi L
2020-01-29 12:16 ` [RFC v3 09/25] vfio: check VFIO_TYPE1_NESTING_IOMMU support Liu, Yi L
2020-02-11 19:08   ` Peter Xu
2020-02-12  7:16     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 10/25] vfio: register DualStageIOMMUObject to vIOMMU Liu, Yi L
2020-01-29 12:16 ` [RFC v3 11/25] vfio: get stage-1 pasid formats from Kernel Liu, Yi L
2020-02-11 19:30   ` Peter Xu
2020-02-12  7:19     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 12/25] vfio/common: add pasid_alloc/free support Liu, Yi L
2020-02-11 19:31   ` Peter Xu
2020-02-12  7:20     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 13/25] intel_iommu: modify x-scalable-mode to be string option Liu, Yi L
2020-02-11 19:43   ` Peter Xu
2020-02-12  7:28     ` Liu, Yi L
2020-02-12 16:05       ` Peter Xu
2020-02-13  2:44         ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 14/25] intel_iommu: add virtual command capability support Liu, Yi L
2020-02-11 20:16   ` Peter Xu
2020-02-12  7:32     ` Liu, Yi L
2020-02-11 21:56   ` Peter Xu
2020-02-13  2:40     ` Liu, Yi L
2020-02-13 14:31       ` Peter Xu
2020-02-13 15:08         ` Peter Xu
2020-02-15  8:49           ` Liu, Yi L [this message]
2020-01-29 12:16 ` [RFC v3 15/25] intel_iommu: process pasid cache invalidation Liu, Yi L
2020-02-11 20:17   ` Peter Xu
2020-02-12  7:33     ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 16/25] intel_iommu: add PASID cache management infrastructure Liu, Yi L
2020-02-11 23:35   ` Peter Xu
2020-02-12  8:37     ` Liu, Yi L
2020-02-12 15:26       ` Peter Xu
2020-02-13  2:59         ` Liu, Yi L
2020-02-13 15:14           ` Peter Xu
2020-02-15  8:50             ` Liu, Yi L
2020-01-29 12:16 ` [RFC v3 17/25] vfio: add bind stage-1 page table support Liu, Yi L
2020-01-29 12:16 ` [RFC v3 18/25] intel_iommu: bind/unbind guest page table to host Liu, Yi L
2020-01-29 12:16 ` [RFC v3 19/25] intel_iommu: replay guest pasid bindings " Liu, Yi L
2020-01-29 12:16 ` [RFC v3 20/25] intel_iommu: replay pasid binds after context cache invalidation Liu, Yi L
2020-01-29 12:16 ` [RFC v3 21/25] intel_iommu: do not pass down pasid bind for PASID #0 Liu, Yi L
2020-01-29 12:16 ` [RFC v3 22/25] vfio: add support for flush iommu stage-1 cache Liu, Yi L
2020-01-29 12:16 ` [RFC v3 23/25] intel_iommu: process PASID-based iotlb invalidation Liu, Yi L
2020-01-29 12:16 ` [RFC v3 24/25] intel_iommu: propagate PASID-based iotlb invalidation to host Liu, Yi L
2020-01-29 12:16 ` [RFC v3 25/25] intel_iommu: process PASID-based Device-TLB invalidation Liu, Yi L
2020-01-29 13:44 ` [RFC v3 00/25] intel_iommu: expose Shared Virtual Addressing to VMs no-reply
2020-01-29 13:48 ` no-reply

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