From: Peter Xu <peterx@redhat.com>
To: "Liu, Yi L" <yi.l.liu@intel.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Yi Sun <yi.y.sun@linux.intel.com>,
Eduardo Habkost <ehabkost@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"mst@redhat.com" <mst@redhat.com>,
"Tian, Jun J" <jun.j.tian@intel.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"eric.auger@redhat.com" <eric.auger@redhat.com>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"Wu, Hao" <hao.wu@intel.com>, "Sun, Yi Y" <yi.y.sun@intel.com>,
Richard Henderson <rth@twiddle.net>,
"david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>
Subject: Re: [RFC v3 14/25] intel_iommu: add virtual command capability support
Date: Thu, 13 Feb 2020 09:31:10 -0500 [thread overview]
Message-ID: <20200213143110.GA1103216@xz-x1> (raw)
In-Reply-To: <A2975661238FB949B60364EF0F2C25743A1BBBF4@SHSMSX104.ccr.corp.intel.com>
On Thu, Feb 13, 2020 at 02:40:45AM +0000, Liu, Yi L wrote:
> > From: Peter Xu <peterx@redhat.com>
> > Sent: Wednesday, February 12, 2020 5:57 AM
> > To: Liu, Yi L <yi.l.liu@intel.com>
> > Subject: Re: [RFC v3 14/25] intel_iommu: add virtual command capability support
> >
> > On Wed, Jan 29, 2020 at 04:16:45AM -0800, Liu, Yi L wrote:
> > > +/*
> > > + * The basic idea is to let hypervisor to set a range for available
> > > + * PASIDs for VMs. One of the reasons is PASID #0 is reserved by
> > > + * RID_PASID usage. We have no idea how many reserved PASIDs in future,
> > > + * so here just an evaluated value. Honestly, set it as "1" is enough
> > > + * at current stage.
> > > + */
> > > +#define VTD_MIN_HPASID 1
> > > +#define VTD_MAX_HPASID 0xFFFFF
> >
> > One more question: I see that PASID is defined as 20bits long. It's
> > fine. However I start to get confused on how the Scalable Mode PASID
> > Directory could service that much of PASID entries.
> >
> > I'm looking at spec 3.4.3, Figure 3-8.
> >
> > Firstly, we only have two levels for a PASID table. The context entry
> > of a device stores a pointer to the "Scalable Mode PASID Directory"
> > page. I see that there're 2^14 entries in "Scalable Mode PASID
> > Directory" page, each is a "Scalable Mode PASID Table".
> > However... how do we fit in the 4K page if each entry is a pointer of
> > x86_64 (8 bytes) while there're 2^14 entries? A simple math gives me
> > 4K/8 = 512, which means the "Scalable Mode PASID Directory" page can
> > only have 512 entries, then how the 2^14 come from? Hmm??
>
> I checked with Kevin. The spec doesn't say the dir table is 4K. It says 4K
> only for pasid table. Also, if you look at 9.4, scalabe-mode context entry
> includes a PDTS field to specify the actual size of the directory table.
Ah I see. Then it seems to be lost then in this series. Say, I think
vtd_sm_pasid_table_walk() should also stop walking until reaching the
size there, and you need to fetch that size info from the context
entry before walk starts.
>
> > 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. :)
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2020-02-13 14:32 UTC|newest]
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 [this message]
2020-02-13 15:08 ` Peter Xu
2020-02-15 8:49 ` Liu, Yi L
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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