QEMU-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Auger Eric <eric.auger@redhat.com>
To: "Tian, Kevin" <kevin.tian@intel.com>, 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>,
	"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 09:54:12 +0200
Message-ID: <c8b8e80d-0b66-1a7c-28b8-0bd3b013a9e8@redhat.com> (raw)
In-Reply-To: <AADFC41AFE54684AB9EE6CBC0274A5D19D562270@SHSMSX104.ccr.corp.intel.com>

Hi,

On 9/4/19 7:46 AM, Tian, Kevin wrote:
>> 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? 

In
https://virtualization.linux-foundation.narkive.com/q6XOkO76/rfc-0-3-virtio-iommu-a-paravirtualized-iommu

I found

"
(Note: the semantics of unmap are chosen to be compatible with VFIO's
type1 v2 IOMMU API. This way a device serving as intermediary between
guest and VFIO doesn't have to keep an internal tree of mappings. They are
a bit tighter than VFIO, in that they don't allow unmap spilling outside
mapped regions. Spilling is 'undefined' at the moment, because it should
work in most cases but I don't know if it's worth the added complexity in
devices that are not simply transmitting requests to VFIO. Splitting
mappings won't ever be allowed, but see the relaxed proposal in 3/3 for
more lenient semantics)
"

Thanks

Eric
> 
> 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
2019-09-04  7:54               ` Auger Eric [this message]
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c8b8e80d-0b66-1a7c-28b8-0bd3b013a9e8@redhat.com \
    --to=eric.auger@redhat.com \
    --cc=alex.williamson@redhat.com \
    --cc=bharat.bhushan@nxp.com \
    --cc=eric.auger.pro@gmail.com \
    --cc=jean-philippe@linaro.org \
    --cc=kevin.tian@intel.com \
    --cc=mst@redhat.com \
    --cc=peter.maydell@linaro.org \
    --cc=peterx@redhat.com \
    --cc=qemu-arm@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    --cc=tn@semihalf.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

QEMU-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/qemu-devel/0 qemu-devel/git/0.git
	git clone --mirror https://lore.kernel.org/qemu-devel/1 qemu-devel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 qemu-devel qemu-devel/ https://lore.kernel.org/qemu-devel \
		qemu-devel@nongnu.org qemu-devel@archiver.kernel.org
	public-inbox-index qemu-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.nongnu.qemu-devel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox