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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Peter Xu <peterx@redhat.com>
Cc: "peter.maydell@linaro.org" <peter.maydell@linaro.org>,
	"mst@redhat.com" <mst@redhat.com>,
	"tn@semihalf.com" <tn@semihalf.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Auger Eric <eric.auger@redhat.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
	"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	"bharat.bhushan@nxp.com" <bharat.bhushan@nxp.com>,
	"eric.auger.pro@gmail.com" <eric.auger.pro@gmail.com>
Subject: Re: [Qemu-devel] [PATCH for-4.2 v10 08/15] virtio-iommu: Implement map/unmap
Date: Wed, 4 Sep 2019 05:46:13 +0000
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D19D562270@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <20190904053720.GG30402@xz-x1>

> From: Peter Xu [mailto:peterx@redhat.com]
> Sent: Wednesday, September 4, 2019 1:37 PM
> 
> On Wed, Sep 04, 2019 at 04:23:50AM +0000, Tian, Kevin wrote:
> > > From: Peter Xu [mailto:peterx@redhat.com]
> > > Sent: Wednesday, September 4, 2019 9:44 AM
> > >
> > > On Tue, Sep 03, 2019 at 01:37:11PM +0200, Auger Eric wrote:
> > > > Hi Peter,
> > > >
> > > > On 8/19/19 10:11 AM, Peter Xu wrote:
> > > > > On Tue, Jul 30, 2019 at 07:21:30PM +0200, Eric Auger wrote:
> > > > >
> > > > > [...]
> > > > >
> > > > >> +    mapping = g_tree_lookup(domain->mappings,
> (gpointer)(&interval));
> > > > >> +
> > > > >> +    while (mapping) {
> > > > >> +        viommu_interval current;
> > > > >> +        uint64_t low  = mapping->virt_addr;
> > > > >> +        uint64_t high = mapping->virt_addr + mapping->size - 1;
> > > > >> +
> > > > >> +        current.low = low;
> > > > >> +        current.high = high;
> > > > >> +
> > > > >> +        if (low == interval.low && size >= mapping->size) {
> > > > >> +            g_tree_remove(domain->mappings, (gpointer)(&current));
> > > > >> +            interval.low = high + 1;
> > > > >> +            trace_virtio_iommu_unmap_left_interval(current.low,
> > > current.high,
> > > > >> +                interval.low, interval.high);
> > > > >> +        } else if (high == interval.high && size >= mapping->size) {
> > > > >> +            trace_virtio_iommu_unmap_right_interval(current.low,
> > > current.high,
> > > > >> +                interval.low, interval.high);
> > > > >> +            g_tree_remove(domain->mappings, (gpointer)(&current));
> > > > >> +            interval.high = low - 1;
> > > > >> +        } else if (low > interval.low && high < interval.high) {
> > > > >> +            trace_virtio_iommu_unmap_inc_interval(current.low,
> > > current.high);
> > > > >> +            g_tree_remove(domain->mappings, (gpointer)(&current));
> > > > >> +        } else {
> > > > >> +            break;
> > > > >> +        }
> > > > >> +        if (interval.low >= interval.high) {
> > > > >> +            return VIRTIO_IOMMU_S_OK;
> > > > >> +        } else {
> > > > >> +            mapping = g_tree_lookup(domain->mappings,
> > > (gpointer)(&interval));
> > > > >> +        }
> > > > >> +    }
> > > > >> +
> > > > >> +    if (mapping) {
> > > > >> +        qemu_log_mask(LOG_GUEST_ERROR,
> > > > >> +                      "****** %s: Unmap 0x%"PRIx64" size=0x%"PRIx64
> > > > >> +                     " from 0x%"PRIx64" size=0x%"PRIx64" is not supported\n",
> > > > >> +                     __func__, interval.low, size,
> > > > >> +                     mapping->virt_addr, mapping->size);
> > > > >> +    } else {
> > > > >> +        return VIRTIO_IOMMU_S_OK;
> > > > >> +    }
> > > > >> +
> > > > >> +    return VIRTIO_IOMMU_S_INVAL;
> > > > >
> > > > > Could the above chunk be simplified as something like below?
> > > > >
> > > > >   while ((mapping = g_tree_lookup(domain->mappings, &interval))) {
> > > > >     g_tree_remove(domain->mappings, mapping);
> > > > >   }
> > > > Indeed the code could be simplified. I only need to make sure I don't
> > > > split an existing mapping.
> > >
> > > Hmm... Do we need to still split an existing mapping if necessary?
> > > For example when with this mapping:
> > >
> > >   iova=0x1000, size=0x2000, phys=ADDR1, flags=FLAGS1
> > >
> > > And if we want to unmap the range (iova=0, size=0x2000), then we
> > > should split the existing mappping and leave this one:
> > >
> > >   iova=0x2000, size=0x1000, phys=(ADDR1+0x1000), flags=FLAGS1
> > >
> > > Right?
> > >
> >
> > virtio-iommu spec explicitly disallows partial unmap.
> >
> > 5.11.6.6.1 Driver Requirements: UNMAP request
> >
> > The first address of a range MUST either be the first address of a
> > mapping or be outside any mapping. The last address of a range
> > MUST either be the last address of a mapping or be outside any
> > mapping.
> >
> > 5.11.6.6.2 Device Requirements: UNMAP request
> >
> > If a mapping affected by the range is not covered in its entirety
> > by the range (the UNMAP request would split the mapping),
> > then the device SHOULD set the request status to VIRTIO_IOMMU
> > _S_RANGE, and SHOULD NOT remove any mapping.
> 
> I see, thanks Kevin.
> 
> Though why so strict?  (Sorry if I missed some discussions
> ... pointers welcomed...)
> 
> What I'm thinking is when we want to allocate a bunch of buffers
> (e.g., 1M) while we will also need to be able to free them with
> smaller chunks (e.g., 4K), then it would be even better that we allow
> to allocate a whole 1M buffer within the guest and map it as a whole,
> then we can selectively unmap the pages after used.  If with the
> strict rule, we'll need to map one by one, that can be a total of
> 1M/4K roundtrips.
> 

Sorry I forgot the original discussion. Need Jean to respond. :-)

A possible reason is that no such usage exists today, thus simplification
was made? 

Thanks
Kevin

  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 17:21 [Qemu-devel] [PATCH for-4.2 v10 00/15] VIRTIO-IOMMU device Eric Auger
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 01/15] update-linux-headers: Import virtio_iommu.h Eric Auger
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 02/15] linux-headers: update against 5.3-rc2 Eric Auger
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 03/15] virtio-iommu: Add skeleton Eric Auger
2019-08-15 13:54   ` Peter Xu
2019-08-29 12:18     ` Auger Eric
2019-08-30  1:26       ` Peter Xu
2019-08-30  8:12         ` Auger Eric
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 04/15] virtio-iommu: Decode the command payload Eric Auger
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 05/15] virtio-iommu: Add the iommu regions Eric Auger
2019-08-16  4:00   ` Peter Xu
2019-08-29 12:51     ` Auger Eric
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 06/15] virtio-iommu: Endpoint and domains structs and helpers Eric Auger
2019-08-16  4:17   ` Peter Xu
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 07/15] virtio-iommu: Implement attach/detach command Eric Auger
2019-08-16  4:27   ` Peter Xu
2019-08-29 14:24     ` Auger Eric
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 08/15] virtio-iommu: Implement map/unmap Eric Auger
2019-08-19  8:11   ` Peter Xu
2019-09-03 11:37     ` Auger Eric
2019-09-04  1:44       ` Peter Xu
2019-09-04  4:23         ` Tian, Kevin
2019-09-04  5:37           ` Peter Xu
2019-09-04  5:46             ` Tian, Kevin [this message]
2019-09-04  7:54               ` Auger Eric
2019-09-04  8:32                 ` Peter Xu
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 09/15] virtio-iommu: Implement translate Eric Auger
2019-08-19  8:24   ` Peter Xu
2019-09-03 11:45     ` Auger Eric
2019-09-04  1:58       ` Peter Xu
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 10/15] virtio-iommu: Implement probe request Eric Auger
2019-08-19 12:08   ` Peter Xu
2019-09-03 12:23     ` Auger Eric
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 11/15] virtio-iommu: Expose the IOAPIC MSI reserved region when relevant Eric Auger
2019-07-30 19:38   ` Michael S. Tsirkin
2019-07-30 23:20     ` Tian, Kevin
2019-07-31  9:05       ` Auger Eric
2019-07-31 19:25       ` Michael S. Tsirkin
2019-07-31 19:44         ` Auger Eric
2019-07-31 23:23           ` Tian, Kevin
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 12/15] virtio-iommu: Implement fault reporting Eric Auger
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 13/15] virtio_iommu: Handle reserved regions in translation process Eric Auger
2019-08-19 12:44   ` Peter Xu
2019-09-01  6:38   ` Michael S. Tsirkin
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 14/15] virtio-iommu-pci: Add virtio iommu pci support Eric Auger
2019-07-30 19:35   ` Michael S. Tsirkin
2019-08-01 12:15     ` Auger Eric
2019-08-01 13:06       ` Michael S. Tsirkin
2019-08-01 13:49         ` Auger Eric
2019-09-01  6:40           ` Michael S. Tsirkin
2019-09-04 14:19             ` Auger Eric
2019-09-04 21:36               ` Michael S. Tsirkin
2019-07-30 17:21 ` [Qemu-devel] [PATCH for-4.2 v10 15/15] hw/arm/virt: Add the virtio-iommu device tree mappings Eric Auger

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