linux-kernel - Re: [PATCH] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

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Date:   Tue, 31 Jan 2023 09:32:07 +0800
From:   Nanyong Sun <sunnanyong@...wei.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
        <mst@...hat.com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>, <wangrong68@...wei.com>
Subject: Re: [PATCH] vhost/vdpa: Add MSI translation tables to iommu for
 software-managed MSI

On 2023/1/29 14:02, Jason Wang wrote:
> On Sat, Jan 28, 2023 at 10:25 AM Nanyong Sun <sunnanyong@...wei.com> wrote:
>> From: Rong Wang <wangrong68@...wei.com>
>>
>> Once enable iommu domain for one device, the MSI
>> translation tables have to be there for software-managed MSI.
>> Otherwise, platform with software-managed MSI without an
>> irq bypass function, can not get a correct memory write event
>> from pcie, will not get irqs.
>> The solution is to obtain the MSI phy base address from
>> iommu reserved region, and set it to iommu MSI cookie,
>> then translation tables will be created while request irq.
>>
>> Signed-off-by: Rong Wang <wangrong68@...wei.com>
>> Signed-off-by: Nanyong Sun <sunnanyong@...wei.com>
>> ---
>>   drivers/iommu/iommu.c |  1 +
>>   drivers/vhost/vdpa.c  | 53 ++++++++++++++++++++++++++++++++++++++++---
>>   2 files changed, 51 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index de91dd88705b..f6c65d5d8e2b 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -2623,6 +2623,7 @@ void iommu_get_resv_regions(struct device *dev, struct list_head *list)
>>          if (ops->get_resv_regions)
>>                  ops->get_resv_regions(dev, list);
>>   }
>> +EXPORT_SYMBOL_GPL(iommu_get_resv_regions);
>>
>>   /**
>>    * iommu_put_resv_regions - release resered regions
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index ec32f785dfde..31d3e9ed4cfa 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -1103,6 +1103,48 @@ static ssize_t vhost_vdpa_chr_write_iter(struct kiocb *iocb,
>>          return vhost_chr_write_iter(dev, from);
>>   }
>>
>> +static bool vhost_vdpa_check_sw_msi(struct list_head *dev_resv_regions, phys_addr_t *base)
>> +{
>> +       struct iommu_resv_region *region;
>> +       bool ret = false;
>> +
>> +       list_for_each_entry(region, dev_resv_regions, list) {
>> +               /*
>> +                * The presence of any 'real' MSI regions should take
>> +                * precedence over the software-managed one if the
>> +                * IOMMU driver happens to advertise both types.
>> +                */
>> +               if (region->type == IOMMU_RESV_MSI) {
>> +                       ret = false;
>> +                       break;
>> +               }
>> +
>> +               if (region->type == IOMMU_RESV_SW_MSI) {
>> +                       *base = region->start;
>> +                       ret = true;
>> +               }
>> +       }
>> +
>> +       return ret;
>> +}
> Can we unify this with what VFIO had?
Yes, these two functions are just the same.
Do you think move this function to iommu.c, and export from iommu is a 
good choice?
>
>> +
>> +static int vhost_vdpa_get_msi_cookie(struct iommu_domain *domain, struct device *dma_dev)
>> +{
>> +       struct list_head dev_resv_regions;
>> +       phys_addr_t resv_msi_base = 0;
>> +       int ret = 0;
>> +
>> +       INIT_LIST_HEAD(&dev_resv_regions);
>> +       iommu_get_resv_regions(dma_dev, &dev_resv_regions);
>> +
>> +       if (vhost_vdpa_check_sw_msi(&dev_resv_regions, &resv_msi_base))
>> +               ret = iommu_get_msi_cookie(domain, resv_msi_base);
>> +
>> +       iommu_put_resv_regions(dma_dev, &dev_resv_regions);
>> +
>> +       return ret;
>> +}
>> +
>>   static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
>>   {
>>          struct vdpa_device *vdpa = v->vdpa;
>> @@ -1128,11 +1170,16 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
>>
>>          ret = iommu_attach_device(v->domain, dma_dev);
>>          if (ret)
>> -               goto err_attach;
>> +               goto err_alloc_domain;
>>
>> -       return 0;
>> +       ret = vhost_vdpa_get_msi_cookie(v->domain, dma_dev);
> Do we need to check the overlap mapping and record it in the interval
> tree (as what VFIO did)?
>
> Thanks
Yes, we need to care about this part, I will handle this recently.
Thanks a lot.
>> +       if (ret)
>> +               goto err_attach_device;
>>
>> -err_attach:
>> +       return 0;
>> +err_attach_device:
>> +       iommu_detach_device(v->domain, dma_dev);
>> +err_alloc_domain:
>>          iommu_domain_free(v->domain);
>>          return ret;
>>   }
>> --
>> 2.25.1
>>
> .