Re: [PATCH 2/2] iommu/virtio: Add ops->flush_iotlb_all and enable deferred flush

[Eric Auger <eric.auger@redhat.com>]

Hi,

On 9/6/23 15:20, Jean-Philippe Brucker wrote:
> On Wed, Sep 06, 2023 at 09:55:49AM +0200, Niklas Schnelle wrote:
>> On Mon, 2023-09-04 at 17:33 +0100, Robin Murphy wrote:
>>> On 2023-09-04 16:34, Jean-Philippe Brucker wrote:
>>>> On Fri, Aug 25, 2023 at 05:21:26PM +0200, Niklas Schnelle wrote:
>>>>> Add ops->flush_iotlb_all operation to enable virtio-iommu for the
>>>>> dma-iommu deferred flush scheme. This results inn a significant increase
>>>> in
>>>>
>>>>> in performance in exchange for a window in which devices can still
>>>>> access previously IOMMU mapped memory. To get back to the prior behavior
>>>>> iommu.strict=1 may be set on the kernel command line.
>>>> Maybe add that it depends on CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT} as
>>>> well, because I've seen kernel configs that enable either.
>>> Indeed, I'd be inclined phrase it in terms of the driver now actually 
>>> being able to honour lazy mode when requested (which happens to be the 
>>> default on x86), rather than as if it might be some 
>>> potentially-unexpected change in behaviour.
>>>
>>> Thanks,
>>> Robin.
>> I kept running this series on a KVM guest on my private workstation
>> (QEMU v8.0.4) and while running iperf3 on a passed-through Intel 82599
>> VF. I got a bunch of IOMMU events similar to the following as well as
>> card resets in the host.
>>
>> ..
>> [ 5959.338214] vfio-pci 0000:04:10.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0037 address=0x7b657064 flags=0x0000]
>> [ 5963.353429] ixgbe 0000:03:00.0 enp3s0: Detected Tx Unit Hang
>>                  Tx Queue             <0>
>>                  TDH, TDT             <93>, <9d>
>>                  next_to_use          <9d>
>>                  next_to_clean        <93>
>>                tx_buffer_info[next_to_clean]
>>                  time_stamp           <10019e800>
>>                  jiffies              <10019ec80>
>> ...
>>
>> I retested on v6.5 vanilla (guest & host) and still get the above
>> errors so luckily for me it doesn't seem to be caused by the new code
>> but I can't reproduce it without virtio-iommu. Any idea what could
>> cause this?
> Adding Eric in case this looks familiar.
Unfortunately no idea of what could cause those page faults. On ther
other hand I mostly test on ARM and INTEL.

Thanks

Eric
>
> I don't have hardware to test this but I guess QEMU system emulation may
> be able to reproduce the issue since it has an AMD IOMMU (unmaintained)
> and igb, I can give that a try.
>
> Thanks,
> Jean
>
>>>>> Link: https://lore.kernel.org/lkml/20230802123612.GA6142@myrica/
>>>>> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
>>>>> ---
>>>>>   drivers/iommu/virtio-iommu.c | 12 ++++++++++++
>>>>>   1 file changed, 12 insertions(+)
>>>>>
>>>>> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
>>>>> index fb73dec5b953..1b7526494490 100644
>>>>> --- a/drivers/iommu/virtio-iommu.c
>>>>> +++ b/drivers/iommu/virtio-iommu.c
>>>>> @@ -924,6 +924,15 @@ static int viommu_iotlb_sync_map(struct iommu_domain *domain,
>>>>>   	return viommu_sync_req(vdomain->viommu);
>>>>>   }
>>>>>   
>>>>> +static void viommu_flush_iotlb_all(struct iommu_domain *domain)
>>>>> +{
>>>>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>>>>> +
>>>>> +	if (!vdomain->nr_endpoints)
>>>>> +		return;
>>>> As for patch 1, a NULL check in viommu_sync_req() would allow dropping
>>>> this one
>>>>
>>>> Thanks,
>>>> Jean
>> Right, makes sense will move the check into viommu_sync_req() and add a
>> coment that it is there fore the cases where viommu_iotlb_sync() et al
>> get called before the IOMMU is set up.
>>
>>>>> +	viommu_sync_req(vdomain->viommu);
>>>>> +}
>>>>> +
>>>>>   static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
>>>>>   {
>>>>>   	struct iommu_resv_region *entry, *new_entry, *msi = NULL;
>>>>> @@ -1049,6 +1058,8 @@ static bool viommu_capable(struct device *dev, enum iommu_cap cap)
>>>>>   	switch (cap) {
>>>>>   	case IOMMU_CAP_CACHE_COHERENCY:
>>>>>   		return true;
>>>>> +	case IOMMU_CAP_DEFERRED_FLUSH:
>>>>> +		return true;
>>>>>   	default:
>>>>>   		return false;
>>>>>   	}
>>>>> @@ -1069,6 +1080,7 @@ static struct iommu_ops viommu_ops = {
>>>>>   		.map_pages		= viommu_map_pages,
>>>>>   		.unmap_pages		= viommu_unmap_pages,
>>>>>   		.iova_to_phys		= viommu_iova_to_phys,
>>>>> +		.flush_iotlb_all	= viommu_flush_iotlb_all,
>>>>>   		.iotlb_sync		= viommu_iotlb_sync,
>>>>>   		.iotlb_sync_map		= viommu_iotlb_sync_map,
>>>>>   		.free			= viommu_domain_free,
>>>>>
>>>>> -- 
>>>>> 2.39.2
>>>>>

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