Re: [PATCH v1 3/6] intel_iommu: Add a framework to check and sync host IOMMU cap/ecap

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 13, 2024 at 07:54:11AM +0000, Duan, Zhenzhong wrote:
> 
> 
> >-----Original Message-----
> >From: Michael S. Tsirkin <mst@redhat.com>
> >Subject: Re: [PATCH v1 3/6] intel_iommu: Add a framework to check and
> >sync host IOMMU cap/ecap
> >
> >On Wed, Mar 13, 2024 at 02:52:39AM +0000, Duan, Zhenzhong wrote:
> >> Hi Michael,
> >>
> >> >-----Original Message-----
> >> >From: Michael S. Tsirkin <mst@redhat.com>
> >> >Subject: Re: [PATCH v1 3/6] intel_iommu: Add a framework to check and
> >> >sync host IOMMU cap/ecap
> >> >
> >> >On Wed, Feb 28, 2024 at 05:44:29PM +0800, Zhenzhong Duan wrote:
> >> >> From: Yi Liu <yi.l.liu@intel.com>
> >> >>
> >> >> Add a framework to check and synchronize host IOMMU cap/ecap with
> >> >> vIOMMU cap/ecap.
> >> >>
> >> >> The sequence will be:
> >> >>
> >> >> vtd_cap_init() initializes iommu->cap/ecap.
> >> >> vtd_check_hdev() update iommu->cap/ecap based on host cap/ecap.
> >> >> iommu->cap_frozen set when machine create done, iommu->cap/ecap
> >> >become readonly.
> >> >>
> >> >> Implementation details for different backends will be in following
> >patches.
> >> >>
> >> >> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> >> >> Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
> >> >> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> >> >> ---
> >> >>  include/hw/i386/intel_iommu.h |  1 +
> >> >>  hw/i386/intel_iommu.c         | 50
> >> >++++++++++++++++++++++++++++++++++-
> >> >>  2 files changed, 50 insertions(+), 1 deletion(-)
> >> >>
> >> >> diff --git a/include/hw/i386/intel_iommu.h
> >> >b/include/hw/i386/intel_iommu.h
> >> >> index bbc7b96add..c71a133820 100644
> >> >> --- a/include/hw/i386/intel_iommu.h
> >> >> +++ b/include/hw/i386/intel_iommu.h
> >> >> @@ -283,6 +283,7 @@ struct IntelIOMMUState {
> >> >>
> >> >>      uint64_t cap;                   /* The value of capability reg */
> >> >>      uint64_t ecap;                  /* The value of extended capability reg */
> >> >> +    bool cap_frozen;                /* cap/ecap become read-only after
> >frozen */
> >> >>
> >> >>      uint32_t context_cache_gen;     /* Should be in [1,MAX] */
> >> >>      GHashTable *iotlb;              /* IOTLB */
> >> >> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> >> >> index ffa1ad6429..a9f9dfd6a7 100644
> >> >> --- a/hw/i386/intel_iommu.c
> >> >> +++ b/hw/i386/intel_iommu.c
> >> >> @@ -35,6 +35,8 @@
> >> >>  #include "sysemu/kvm.h"
> >> >>  #include "sysemu/dma.h"
> >> >>  #include "sysemu/sysemu.h"
> >> >> +#include "hw/vfio/vfio-common.h"
> >> >> +#include "sysemu/iommufd.h"
> >> >>  #include "hw/i386/apic_internal.h"
> >> >>  #include "kvm/kvm_i386.h"
> >> >>  #include "migration/vmstate.h"
> >> >> @@ -3819,6 +3821,38 @@ VTDAddressSpace
> >> >*vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus,
> >> >>      return vtd_dev_as;
> >> >>  }
> >> >>
> >> >> +static int vtd_check_legacy_hdev(IntelIOMMUState *s,
> >> >> +                                 IOMMULegacyDevice *ldev,
> >> >> +                                 Error **errp)
> >> >> +{
> >> >> +    return 0;
> >> >> +}
> >> >> +
> >> >> +static int vtd_check_iommufd_hdev(IntelIOMMUState *s,
> >> >> +                                  IOMMUFDDevice *idev,
> >> >> +                                  Error **errp)
> >> >> +{
> >> >> +    return 0;
> >> >> +}
> >> >> +
> >> >> +static int vtd_check_hdev(IntelIOMMUState *s,
> >VTDHostIOMMUDevice
> >> >*vtd_hdev,
> >> >> +                          Error **errp)
> >> >> +{
> >> >> +    HostIOMMUDevice *base_dev = vtd_hdev->dev;
> >> >> +    IOMMUFDDevice *idev;
> >> >> +
> >> >> +    if (base_dev->type == HID_LEGACY) {
> >> >> +        IOMMULegacyDevice *ldev = container_of(base_dev,
> >> >> +                                               IOMMULegacyDevice, base);
> >> >> +
> >> >> +        return vtd_check_legacy_hdev(s, ldev, errp);
> >> >> +    }
> >> >> +
> >> >> +    idev = container_of(base_dev, IOMMUFDDevice, base);
> >> >> +
> >> >> +    return vtd_check_iommufd_hdev(s, idev, errp);
> >> >> +}
> >> >> +
> >> >>  static int vtd_dev_set_iommu_device(PCIBus *bus, void *opaque, int
> >> >devfn,
> >> >>                                      HostIOMMUDevice *base_dev, Error **errp)
> >> >>  {
> >> >> @@ -3829,6 +3863,7 @@ static int
> >vtd_dev_set_iommu_device(PCIBus
> >> >*bus, void *opaque, int devfn,
> >> >>          .devfn = devfn,
> >> >>      };
> >> >>      struct vtd_as_key *new_key;
> >> >> +    int ret;
> >> >>
> >> >>      assert(base_dev);
> >> >>
> >> >> @@ -3848,6 +3883,13 @@ static int
> >vtd_dev_set_iommu_device(PCIBus
> >> >*bus, void *opaque, int devfn,
> >> >>      vtd_hdev->iommu_state = s;
> >> >>      vtd_hdev->dev = base_dev;
> >> >>
> >> >> +    ret = vtd_check_hdev(s, vtd_hdev, errp);
> >> >> +    if (ret) {
> >> >> +        g_free(vtd_hdev);
> >> >> +        vtd_iommu_unlock(s);
> >> >> +        return ret;
> >> >> +    }
> >> >> +
> >> >>      new_key = g_malloc(sizeof(*new_key));
> >> >>      new_key->bus = bus;
> >> >>      new_key->devfn = devfn;
> >> >
> >> >
> >> >Okay. So when VFIO device is created, it will call
> >vtd_dev_set_iommu_device
> >> >and that in turn will update caps.
> >> >
> >> >
> >> >
> >> >
> >> >> @@ -4083,7 +4125,9 @@ static void vtd_init(IntelIOMMUState *s)
> >> >>      s->iq_dw = false;
> >> >>      s->next_frcd_reg = 0;
> >> >>
> >> >> -    vtd_cap_init(s);
> >> >> +    if (!s->cap_frozen) {
> >> >> +        vtd_cap_init(s);
> >> >> +    }
> >> >>
> >> >
> >> >If it's fronzen it's because VFIO was added after machine done.
> >> >And then what? I think caps are just wrong?
> >>
> >> Not quite get your question on caps being wrong. But try to explains:
> >>
> >> When a hot plugged vfio device's host iommu cap isn't compatible with
> >> vIOMMU's, hotplug should fail. Currently there is no check for this and
> >> allow hotplug to succeed, but then some issue will reveal later,
> >> e.g., vIOMMU's MGAW > host IOMMU's MGAW, guest can setup iova
> >> mapping beyond host supported iova range, then DMA will fail.
> >>
> >> In fact, before this series, cap is not impacted by VFIO, so it's same effect of
> >> frozen after machine done.
> >>
> >> >
> >> >
> >> >I think the way to approach this is just by specifying this
> >> >as an option on command line.
> >>
> >> Do you mean add a cap_frozen property to intel_iommu?
> >> Vtd_init() is called in realize() and system reset(), so I utilize realize() to init
> >cap
> >> and froze cap before system reset(). If cap_frozen is an option, when it's
> >set to
> >> false, cap could be updated every system reset and it's not a fix value any
> >more.
> >> This may break migration.
> >
> >No, I mean either
> >1. add some kind of vfio-iommu device that is not exposed to guest
> >   but is not hot pluggable
> 
> Not quite get, what will such vfio-iommu device be used for if not exposed to guest.

It will update the IOMMU.
And do so without need for tricky callbacks.

-- 
MST