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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Yan Zhao" <yan.y.zhao@intel.com>,
	"Juan Quintela" <quintela@redhat.com>,
	qemu-devel@nongnu.org, "Peter Xu" <peterx@redhat.com>,
	"Eugenio Pérez" <eperezma@redhat.com>,
	"Eric Auger" <eric.auger@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier
Date: Tue, 30 Jun 2020 17:23:31 +0800
Message-ID: <49f547e1-dd87-7abe-1075-9dcece75b641@redhat.com> (raw)
In-Reply-To: <20200630052148-mutt-send-email-mst@kernel.org>


On 2020/6/30 下午5:21, Michael S. Tsirkin wrote:
> On Tue, Jun 30, 2020 at 04:29:19PM +0800, Jason Wang wrote:
>> On 2020/6/30 上午10:41, Jason Wang wrote:
>>> On 2020/6/29 下午9:34, Peter Xu wrote:
>>>> On Mon, Jun 29, 2020 at 01:51:47PM +0800, Jason Wang wrote:
>>>>> On 2020/6/28 下午10:47, Peter Xu wrote:
>>>>>> On Sun, Jun 28, 2020 at 03:03:41PM +0800, Jason Wang wrote:
>>>>>>> On 2020/6/27 上午5:29, Peter Xu wrote:
>>>>>>>> Hi, Eugenio,
>>>>>>>>
>>>>>>>> (CCing Eric, Yan and Michael too)
>>>>>>>>
>>>>>>>> On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio Pérez wrote:
>>>>>>>>> diff --git a/memory.c b/memory.c
>>>>>>>>> index 2f15a4b250..7f789710d2 100644
>>>>>>>>> --- a/memory.c
>>>>>>>>> +++ b/memory.c
>>>>>>>>> @@ -1915,8 +1915,6 @@ void
>>>>>>>>> memory_region_notify_one(IOMMUNotifier
>>>>>>>>> *notifier,
>>>>>>>>>              return;
>>>>>>>>>          }
>>>>>>>>> -    assert(entry->iova >= notifier->start &&
>>>>>>>>> entry_end <= notifier->end);
>>>>>>>> I can understand removing the assertion should solve
>>>>>>>> the issue, however imho
>>>>>>>> the major issue is not about this single assertion
>>>>>>>> but the whole addr_mask
>>>>>>>> issue behind with virtio...
>>>>>>> I don't get here, it looks to the the range was from
>>>>>>> guest IOMMU drivers.
>>>>>> Yes.  Note that I didn't mean that it's a problem in virtio,
>>>>>> it's just the fact
>>>>>> that virtio is the only one I know that would like to
>>>>>> support arbitrary address
>>>>>> range for the translated region.  I don't know about tcg,
>>>>>> but vfio should still
>>>>>> need some kind of page alignment in both the address and the
>>>>>> addr_mask.  We
>>>>>> have that assumption too across the memory core when we do
>>>>>> translations.
>>>>> Right but it looks to me the issue is not the alignment.
>>>>>
>>>>>
>>>>>> A further cause of the issue is the MSI region when vIOMMU
>>>>>> enabled - currently
>>>>>> we implemented the interrupt region using another memory
>>>>>> region so it split the
>>>>>> whole DMA region into two parts.  That's really a clean approach to IR
>>>>>> implementation, however that's also a burden to the
>>>>>> invalidation part because
>>>>>> then we'll need to handle things like this when the listened
>>>>>> range is not page
>>>>>> alighed at all (neither 0-0xfedffff, nor 0xfef0000-MAX).  If
>>>>>> without the IR
>>>>>> region (so the whole iommu address range will be a single FlatRange),
>>>>> Is this a bug? I remember that at least for vtd, it won't do any
>>>>> DMAR on the
>>>>> intrrupt address range
>>>> I don't think it's a bug, at least it's working as how I
>>>> understand...  that
>>>> interrupt range is using an IR region, that's why I said the IR
>>>> region splits
>>>> the DMAR region into two pieces, so we have two FlatRange for the same
>>>> IOMMUMemoryRegion.
>>>
>>> I don't check the qemu code but if "a single FlatRange" means
>>> 0xFEEx_xxxx is subject to DMA remapping, OS need to setup passthrough
>>> mapping for that range in order to get MSI to work. This is not what vtd
>>> spec said:
>>>
>>> """
>>>
>>> 3.14 Handling Requests to Interrupt Address Range
>>>
>>> Requests without PASID to address range 0xFEEx_xxxx are treated as
>>> potential interrupt requests and are not subjected to DMA remapping
>>> (even if translation structures specify a mapping for this
>>> range). Instead, remapping hardware can be enabled to subject such
>>> interrupt requests to interrupt remapping.
>>>
>>> """
>>>
>>> My understanding is vtd won't do any DMA translation on 0xFEEx_xxxx even
>>> if IR is not enabled.
>>
>> Ok, we had a dedicated mr for interrupt:
>>
>> memory_region_add_subregion_overlap(MEMORY_REGION(&vtd_dev_as->iommu),
>> VTD_INTERRUPT_ADDR_FIRST,
>> &vtd_dev_as->iommu_ir, 1);
>>
>> So it should be fine. I guess the reason that I'm asking is that I thought
>> "IR" means "Interrupt remapping" but in fact it means "Interrupt Region"?
>>
>> But I'm still not clear about the invalidation part for interrupt region,
>> maybe you can elaborate a little more on this.
>>
>> Btw, I think guest can trigger the assert in vtd_do_iommu_translate() if we
>> teach vhost to DMA to that region:
>
> Why would we want to?


I meant a buggy(malicious) guest driver.

Thanks


>
>>      /*
>>       * We have standalone memory region for interrupt addresses, we
>>       * should never receive translation requests in this region.
>>       */
>>      assert(!vtd_is_interrupt_addr(addr));
>>
>> Is this better to return false here? (We can work on the fix for vhost but
>> it should be not trivial)
>>
>> Thanks
>>



  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-26  6:41 [RFC v2 0/1] " Eugenio Pérez
2020-06-26  6:41 ` [RFC v2 1/1] " Eugenio Pérez
2020-06-26 21:29   ` Peter Xu
2020-06-27  7:26     ` Yan Zhao
2020-06-27 12:57       ` Peter Xu
2020-06-28  1:36         ` Yan Zhao
2020-06-28  7:03     ` Jason Wang
2020-06-28 14:47       ` Peter Xu
2020-06-29  5:51         ` Jason Wang
2020-06-29 13:34           ` Peter Xu
2020-06-30  2:41             ` Jason Wang
2020-06-30  8:29               ` Jason Wang
2020-06-30  9:21                 ` Michael S. Tsirkin
2020-06-30  9:23                   ` Jason Wang [this message]
2020-06-30 15:20                     ` Peter Xu
2020-07-01  8:11                       ` Jason Wang
2020-07-01 12:16                         ` Peter Xu
2020-07-01 12:30                           ` Jason Wang
2020-07-01 12:41                             ` Peter Xu
2020-07-02  3:00                               ` Jason Wang
2020-06-30 15:39               ` Peter Xu
2020-07-01  8:09                 ` Jason Wang
2020-07-02  3:01                   ` Jason Wang
2020-07-02 15:45                     ` Peter Xu
2020-07-03  7:24                       ` Jason Wang
2020-07-03 13:03                         ` Peter Xu
2020-07-07  8:03                           ` Jason Wang
2020-07-07 19:54                             ` Peter Xu
2020-07-08  5:42                               ` Jason Wang
2020-07-08 14:16                                 ` Peter Xu
2020-07-09  5:58                                   ` Jason Wang
2020-07-09 14:10                                     ` Peter Xu
2020-07-10  6:34                                       ` Jason Wang
2020-07-10 13:30                                         ` Peter Xu
2020-07-13  4:04                                           ` Jason Wang
2020-07-16  1:00                                             ` Peter Xu
2020-07-16  2:54                                               ` Jason Wang
2020-07-17 14:18                                                 ` Peter Xu
2020-07-20  4:02                                                   ` Jason Wang
2020-07-20 13:03                                                     ` Peter Xu
2020-07-21  6:20                                                       ` Jason Wang
2020-07-21 15:10                                                         ` Peter Xu
2020-08-03 16:00                         ` Eugenio Pérez
2020-08-04 20:30                           ` Peter Xu
2020-08-05  5:45                             ` Jason Wang
2020-06-29 15:05 ` [RFC v2 0/1] " Paolo Bonzini
2020-07-03  7:39   ` Eugenio Perez Martin
2020-07-03 10:10     ` Paolo Bonzini

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