[PATCH 0/6] VT-d: domain ID mapping improvements

[PATCH 0/6] VT-d: domain ID mapping improvements

[Jan Beulich]

Two bug fixes, some cleanup, and a simplification for modern hardware.

1: properly reserve DID 0 for caching mode IOMMUs
2: split domid map cleanup check into a function
3: don't leak domid mapping on error path
4: tidy domid map handling
5: introduce helper to convert DID to domid_t
6: avoid allocating domid_{bit,}map[] when possible

This depends on the previously submitted (and already approved, except
for a possible release ack) "VT-d: per-domain IOMMU bitmap needs to
have dynamic size".

Jan

[PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Jan Beulich]

Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
still have DID 0 allocated to it, because of the zero-filling of
domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
used.

Fixes: b9c20c78789f ("VT-d: per-iommu domain-id")
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1257,16 +1257,19 @@ int __init iommu_alloc(struct acpi_drhd_
     if ( !iommu->domid_bitmap )
         return -ENOMEM;
 
+    iommu->domid_map = xzalloc_array(u16, nr_dom);
+    if ( !iommu->domid_map )
+        return -ENOMEM;
+
     /*
-     * if Caching mode is set, then invalid translations are tagged with
-     * domain id 0, Hence reserve bit 0 for it
+     * If Caching mode is set, then invalid translations are tagged with
+     * domain id 0. Hence reserve bit/slot 0.
      */
     if ( cap_caching_mode(iommu->cap) )
+    {
+        iommu->domid_map[0] = DOMID_INVALID;
         __set_bit(0, iommu->domid_bitmap);
-
-    iommu->domid_map = xzalloc_array(u16, nr_dom);
-    if ( !iommu->domid_map )
-        return -ENOMEM;
+    }
 
     return 0;
 }

Re: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
> still have DID 0 allocated to it, because of the zero-filling of
> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
> used.

Shouldn't the whole domid_map be initialized to DOMID_INVALID to
prevent dom0 matching against any unused slot?

Similarly cleanup_domid_map should set the slot to DOMID_INVALID.

Thanks, Roger.

Re: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Jan Beulich]

On 12.11.2021 12:23, Roger Pau Monné wrote:
> On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
>> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
>> still have DID 0 allocated to it, because of the zero-filling of
>> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
>> used.
> 
> Shouldn't the whole domid_map be initialized to DOMID_INVALID to
> prevent dom0 matching against any unused slot?
> 
> Similarly cleanup_domid_map should set the slot to DOMID_INVALID.

I don't think so, that's the purpose of setting the bit in domid_bitmap.
The problem really was only with setting a bit in that bitmap without
invalidating the corresponding slot.

This said, I can still see value in doing as you suggest, but as a
separate change with a different justification. In fact domid_bitmap is
kind of redundant now anyway; aiui it was the thing that existed first.
Then domid_map[] was simply added, rather than fully replacing the
original bitmap.

Jan

Re: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 01:07:33PM +0100, Jan Beulich wrote:
> On 12.11.2021 12:23, Roger Pau Monné wrote:
> > On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
> >> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
> >> still have DID 0 allocated to it, because of the zero-filling of
> >> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
> >> used.
> > 
> > Shouldn't the whole domid_map be initialized to DOMID_INVALID to
> > prevent dom0 matching against any unused slot?
> > 
> > Similarly cleanup_domid_map should set the slot to DOMID_INVALID.
> 
> I don't think so, that's the purpose of setting the bit in domid_bitmap.
> The problem really was only with setting a bit in that bitmap without
> invalidating the corresponding slot.
> 
> This said, I can still see value in doing as you suggest, but as a
> separate change with a different justification. In fact domid_bitmap is
> kind of redundant now anyway; aiui it was the thing that existed first.
> Then domid_map[] was simply added, rather than fully replacing the
> original bitmap.

I guess using domid_bitmap to find a free slot is faster than scanning
the array of iommu IDs to domids. Not sure how performance critical
that search is, so maybe it's fine to just drop domid_bitmap and rely
exclusively on the array.

Thanks, Roger.

RE: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Tian, Kevin]

> From: Roger Pau Monné <roger.pau@citrix.com>
> Sent: Friday, November 12, 2021 8:19 PM
> 
> On Fri, Nov 12, 2021 at 01:07:33PM +0100, Jan Beulich wrote:
> > On 12.11.2021 12:23, Roger Pau Monné wrote:
> > > On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
> > >> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
> > >> still have DID 0 allocated to it, because of the zero-filling of
> > >> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
> > >> used.
> > >
> > > Shouldn't the whole domid_map be initialized to DOMID_INVALID to
> > > prevent dom0 matching against any unused slot?
> > >
> > > Similarly cleanup_domid_map should set the slot to DOMID_INVALID.
> >
> > I don't think so, that's the purpose of setting the bit in domid_bitmap.
> > The problem really was only with setting a bit in that bitmap without
> > invalidating the corresponding slot.
> >
> > This said, I can still see value in doing as you suggest, but as a
> > separate change with a different justification. In fact domid_bitmap is
> > kind of redundant now anyway; aiui it was the thing that existed first.
> > Then domid_map[] was simply added, rather than fully replacing the
> > original bitmap.
> 
> I guess using domid_bitmap to find a free slot is faster than scanning
> the array of iommu IDs to domids. Not sure how performance critical
> that search is, so maybe it's fine to just drop domid_bitmap and rely
> exclusively on the array.
> 

I'm fine to drop domid_bitmap. I don't think domain creation
is in hot path...

Re: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 10:47:59AM +0100, Jan Beulich wrote:
> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
> still have DID 0 allocated to it, because of the zero-filling of
> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
> used.
> 
> Fixes: b9c20c78789f ("VT-d: per-iommu domain-id")
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks, Roger.

RE: [PATCH 1/6] VT-d: properly reserve DID 0 for caching mode IOMMUs

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:48 PM
> 
> Merely setting bit 0 in the bitmap is insufficient, as then Dom0 will
> still have DID 0 allocated to it, because of the zero-filling of
> domid_map[]. Set slot 0 to DOMID_INVALID to keep DID 0 from getting
> used.
> 
> Fixes: b9c20c78789f ("VT-d: per-iommu domain-id")
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1257,16 +1257,19 @@ int __init iommu_alloc(struct acpi_drhd_
>      if ( !iommu->domid_bitmap )
>          return -ENOMEM;
> 
> +    iommu->domid_map = xzalloc_array(u16, nr_dom);
> +    if ( !iommu->domid_map )
> +        return -ENOMEM;
> +
>      /*
> -     * if Caching mode is set, then invalid translations are tagged with
> -     * domain id 0, Hence reserve bit 0 for it
> +     * If Caching mode is set, then invalid translations are tagged with
> +     * domain id 0. Hence reserve bit/slot 0.
>       */
>      if ( cap_caching_mode(iommu->cap) )
> +    {
> +        iommu->domid_map[0] = DOMID_INVALID;
>          __set_bit(0, iommu->domid_bitmap);
> -
> -    iommu->domid_map = xzalloc_array(u16, nr_dom);
> -    if ( !iommu->domid_map )
> -        return -ENOMEM;
> +    }
> 
>      return 0;
>  }

[PATCH 2/6] VT-d: split domid map cleanup check into a function

[Jan Beulich]

This logic will want invoking from elsewhere.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -157,6 +157,51 @@ static void cleanup_domid_map(struct dom
     }
 }
 
+static bool any_pdev_behind_iommu(const struct domain *d,
+                                  const struct pci_dev *exclude,
+                                  const struct vtd_iommu *iommu)
+{
+    const struct pci_dev *pdev;
+
+    for_each_pdev ( d, pdev )
+    {
+        const struct acpi_drhd_unit *drhd;
+
+        if ( pdev == exclude )
+            continue;
+
+        drhd = acpi_find_matched_drhd_unit(pdev);
+        if ( drhd && drhd->iommu == iommu )
+            return true;
+    }
+
+    return false;
+}
+
+/*
+ * If no other devices under the same iommu owned by this domain,
+ * clear iommu in iommu_bitmap and clear domain_id in domid_bitmap.
+ */
+static void check_cleanup_domid_map(struct domain *d,
+                                    const struct pci_dev *exclude,
+                                    struct vtd_iommu *iommu)
+{
+    bool found = any_pdev_behind_iommu(d, exclude, iommu);
+
+    /*
+     * Hidden devices are associated with DomXEN but usable by the hardware
+     * domain. Hence they need considering here as well.
+     */
+    if ( !found && is_hardware_domain(d) )
+        found = any_pdev_behind_iommu(dom_xen, exclude, iommu);
+
+    if ( !found )
+    {
+        clear_bit(iommu->index, dom_iommu(d)->arch.vtd.iommu_bitmap);
+        cleanup_domid_map(d, iommu);
+    }
+}
+
 static void sync_cache(const void *addr, unsigned int size)
 {
     static unsigned long clflush_size = 0;
@@ -1675,27 +1720,6 @@ int domain_context_unmap_one(
     return rc;
 }
 
-static bool any_pdev_behind_iommu(const struct domain *d,
-                                  const struct pci_dev *exclude,
-                                  const struct vtd_iommu *iommu)
-{
-    const struct pci_dev *pdev;
-
-    for_each_pdev ( d, pdev )
-    {
-        const struct acpi_drhd_unit *drhd;
-
-        if ( pdev == exclude )
-            continue;
-
-        drhd = acpi_find_matched_drhd_unit(pdev);
-        if ( drhd && drhd->iommu == iommu )
-            return true;
-    }
-
-    return false;
-}
-
 static int domain_context_unmap(struct domain *domain, u8 devfn,
                                 struct pci_dev *pdev)
 {
@@ -1704,7 +1728,6 @@ static int domain_context_unmap(struct d
     int ret;
     uint16_t seg = pdev->seg;
     uint8_t bus = pdev->bus, tmp_bus, tmp_devfn, secbus;
-    bool found;
 
     switch ( pdev->type )
     {
@@ -1780,28 +1803,10 @@ static int domain_context_unmap(struct d
         return -EINVAL;
     }
 
-    if ( ret || QUARANTINE_SKIP(domain) || pdev->devfn != devfn )
-        return ret;
+    if ( !ret && !QUARANTINE_SKIP(domain) && pdev->devfn == devfn )
+        check_cleanup_domid_map(domain, pdev, iommu);
 
-    /*
-     * If no other devices under the same iommu owned by this domain,
-     * clear iommu in iommu_bitmap and clear domain_id in domid_bitmap.
-     */
-    found = any_pdev_behind_iommu(domain, pdev, iommu);
-    /*
-     * Hidden devices are associated with DomXEN but usable by the hardware
-     * domain. Hence they need considering here as well.
-     */
-    if ( !found && is_hardware_domain(domain) )
-        found = any_pdev_behind_iommu(dom_xen, pdev, iommu);
-
-    if ( !found )
-    {
-        clear_bit(iommu->index, dom_iommu(domain)->arch.vtd.iommu_bitmap);
-        cleanup_domid_map(domain, iommu);
-    }
-
-    return 0;
+    return ret;
 }
 
 static void iommu_clear_root_pgtable(struct domain *d)

Re: [PATCH 2/6] VT-d: split domid map cleanup check into a function

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 10:48:19AM +0100, Jan Beulich wrote:
> This logic will want invoking from elsewhere.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Might be worth to explicitly note this is a non functional change.

Thanks, Roger.

RE: [PATCH 2/6] VT-d: split domid map cleanup check into a function

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:48 PM
> 
> This logic will want invoking from elsewhere.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -157,6 +157,51 @@ static void cleanup_domid_map(struct dom
>      }
>  }
> 
> +static bool any_pdev_behind_iommu(const struct domain *d,
> +                                  const struct pci_dev *exclude,
> +                                  const struct vtd_iommu *iommu)
> +{
> +    const struct pci_dev *pdev;
> +
> +    for_each_pdev ( d, pdev )
> +    {
> +        const struct acpi_drhd_unit *drhd;
> +
> +        if ( pdev == exclude )
> +            continue;
> +
> +        drhd = acpi_find_matched_drhd_unit(pdev);
> +        if ( drhd && drhd->iommu == iommu )
> +            return true;
> +    }
> +
> +    return false;
> +}
> +
> +/*
> + * If no other devices under the same iommu owned by this domain,
> + * clear iommu in iommu_bitmap and clear domain_id in domid_bitmap.
> + */
> +static void check_cleanup_domid_map(struct domain *d,
> +                                    const struct pci_dev *exclude,
> +                                    struct vtd_iommu *iommu)
> +{
> +    bool found = any_pdev_behind_iommu(d, exclude, iommu);
> +
> +    /*
> +     * Hidden devices are associated with DomXEN but usable by the
> hardware
> +     * domain. Hence they need considering here as well.
> +     */
> +    if ( !found && is_hardware_domain(d) )
> +        found = any_pdev_behind_iommu(dom_xen, exclude, iommu);
> +
> +    if ( !found )
> +    {
> +        clear_bit(iommu->index, dom_iommu(d)->arch.vtd.iommu_bitmap);
> +        cleanup_domid_map(d, iommu);
> +    }
> +}
> +
>  static void sync_cache(const void *addr, unsigned int size)
>  {
>      static unsigned long clflush_size = 0;
> @@ -1675,27 +1720,6 @@ int domain_context_unmap_one(
>      return rc;
>  }
> 
> -static bool any_pdev_behind_iommu(const struct domain *d,
> -                                  const struct pci_dev *exclude,
> -                                  const struct vtd_iommu *iommu)
> -{
> -    const struct pci_dev *pdev;
> -
> -    for_each_pdev ( d, pdev )
> -    {
> -        const struct acpi_drhd_unit *drhd;
> -
> -        if ( pdev == exclude )
> -            continue;
> -
> -        drhd = acpi_find_matched_drhd_unit(pdev);
> -        if ( drhd && drhd->iommu == iommu )
> -            return true;
> -    }
> -
> -    return false;
> -}
> -
>  static int domain_context_unmap(struct domain *domain, u8 devfn,
>                                  struct pci_dev *pdev)
>  {
> @@ -1704,7 +1728,6 @@ static int domain_context_unmap(struct d
>      int ret;
>      uint16_t seg = pdev->seg;
>      uint8_t bus = pdev->bus, tmp_bus, tmp_devfn, secbus;
> -    bool found;
> 
>      switch ( pdev->type )
>      {
> @@ -1780,28 +1803,10 @@ static int domain_context_unmap(struct d
>          return -EINVAL;
>      }
> 
> -    if ( ret || QUARANTINE_SKIP(domain) || pdev->devfn != devfn )
> -        return ret;
> +    if ( !ret && !QUARANTINE_SKIP(domain) && pdev->devfn == devfn )
> +        check_cleanup_domid_map(domain, pdev, iommu);
> 
> -    /*
> -     * If no other devices under the same iommu owned by this domain,
> -     * clear iommu in iommu_bitmap and clear domain_id in domid_bitmap.
> -     */
> -    found = any_pdev_behind_iommu(domain, pdev, iommu);
> -    /*
> -     * Hidden devices are associated with DomXEN but usable by the
> hardware
> -     * domain. Hence they need considering here as well.
> -     */
> -    if ( !found && is_hardware_domain(domain) )
> -        found = any_pdev_behind_iommu(dom_xen, pdev, iommu);
> -
> -    if ( !found )
> -    {
> -        clear_bit(iommu->index, dom_iommu(domain)-
> >arch.vtd.iommu_bitmap);
> -        cleanup_domid_map(domain, iommu);
> -    }
> -
> -    return 0;
> +    return ret;
>  }
> 
>  static void iommu_clear_root_pgtable(struct domain *d)

[PATCH 3/6] VT-d: don't leak domid mapping on error path

[Jan Beulich]

While domain_context_mapping() invokes domain_context_unmap() in a sub-
case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
a leak, individual calls to domain_context_mapping_one() aren't
similarly covered. Such a leak might persist until domain destruction.
Leverage that these cases can be recognized by pdev being non-NULL.

Fixes: dec403cc668f ("VT-d: fix iommu_domid for PCI/PCIx devices assignment")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
The Fixes: tag isn't strictly correct, as error handling had more severe
shortcomings at the time. But I wouldn't want to blame a commit
improving error handling to have introduced the leak.

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1518,7 +1518,12 @@ int domain_context_mapping_one(
         rc = me_wifi_quirk(domain, bus, devfn, MAP_ME_PHANTOM_FUNC);
 
     if ( rc )
-        domain_context_unmap_one(domain, iommu, bus, devfn);
+    {
+        ret = domain_context_unmap_one(domain, iommu, bus, devfn);
+
+        if ( !ret && pdev && pdev->devfn == devfn )
+            check_cleanup_domid_map(domain, pdev, iommu);
+    }
 
     return rc;
 }

Re: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 10:48:43AM +0100, Jan Beulich wrote:
> While domain_context_mapping() invokes domain_context_unmap() in a sub-
> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
> a leak, individual calls to domain_context_mapping_one() aren't
> similarly covered. Such a leak might persist until domain destruction.
> Leverage that these cases can be recognized by pdev being non-NULL.

Would it help to place the domid cleanup in domain_context_unmap_one,
as that would then cover calls from domain_context_unmap and the
failure path in domain_context_mapping_one.

Thanks, Roger.

Re: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Jan Beulich]

On 12.11.2021 14:42, Roger Pau Monné wrote:
> On Fri, Nov 12, 2021 at 10:48:43AM +0100, Jan Beulich wrote:
>> While domain_context_mapping() invokes domain_context_unmap() in a sub-
>> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
>> a leak, individual calls to domain_context_mapping_one() aren't
>> similarly covered. Such a leak might persist until domain destruction.
>> Leverage that these cases can be recognized by pdev being non-NULL.
> 
> Would it help to place the domid cleanup in domain_context_unmap_one,
> as that would then cover calls from domain_context_unmap and the
> failure path in domain_context_mapping_one.

I don't think that would work (without further convolution), because of
the up to 3 successive calls in DEV_TYPE_PCI handling. Cleanup may happen
only on the first map's error path or after the last unmap.

Jan

Re: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Roger Pau Monné]

On Fri, Nov 12, 2021 at 02:45:14PM +0100, Jan Beulich wrote:
> On 12.11.2021 14:42, Roger Pau Monné wrote:
> > On Fri, Nov 12, 2021 at 10:48:43AM +0100, Jan Beulich wrote:
> >> While domain_context_mapping() invokes domain_context_unmap() in a sub-
> >> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
> >> a leak, individual calls to domain_context_mapping_one() aren't
> >> similarly covered. Such a leak might persist until domain destruction.
> >> Leverage that these cases can be recognized by pdev being non-NULL.
> > 
> > Would it help to place the domid cleanup in domain_context_unmap_one,
> > as that would then cover calls from domain_context_unmap and the
> > failure path in domain_context_mapping_one.
> 
> I don't think that would work (without further convolution), because of
> the up to 3 successive calls in DEV_TYPE_PCI handling. Cleanup may happen
> only on the first map's error path or after the last unmap.

Hm, I see. And AFAICT that's because some devices that get assigned to
a guest iommu context are not actually assigned to the guest (ie:
pdev->domain doesn't get set, neither the device is added to the
per-domain list), which makes them invisible to
any_pdev_behind_iommu.

I dislike that the domid is added in domain_context_mapping_one, while
the cleanup is not done in domain_context_unmap_one, and that some
devices context could be using the domain id without being assigned to
the domain.

Thanks, Roger.

Re: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Jan Beulich]

On 12.11.2021 15:35, Roger Pau Monné wrote:
> On Fri, Nov 12, 2021 at 02:45:14PM +0100, Jan Beulich wrote:
>> On 12.11.2021 14:42, Roger Pau Monné wrote:
>>> On Fri, Nov 12, 2021 at 10:48:43AM +0100, Jan Beulich wrote:
>>>> While domain_context_mapping() invokes domain_context_unmap() in a sub-
>>>> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
>>>> a leak, individual calls to domain_context_mapping_one() aren't
>>>> similarly covered. Such a leak might persist until domain destruction.
>>>> Leverage that these cases can be recognized by pdev being non-NULL.
>>>
>>> Would it help to place the domid cleanup in domain_context_unmap_one,
>>> as that would then cover calls from domain_context_unmap and the
>>> failure path in domain_context_mapping_one.
>>
>> I don't think that would work (without further convolution), because of
>> the up to 3 successive calls in DEV_TYPE_PCI handling. Cleanup may happen
>> only on the first map's error path or after the last unmap.
> 
> Hm, I see. And AFAICT that's because some devices that get assigned to
> a guest iommu context are not actually assigned to the guest (ie:
> pdev->domain doesn't get set, neither the device is added to the
> per-domain list), which makes them invisible to
> any_pdev_behind_iommu.
> 
> I dislike that the domid is added in domain_context_mapping_one, while
> the cleanup is not done in domain_context_unmap_one, and that some
> devices context could be using the domain id without being assigned to
> the domain.

This all isn't really pretty, is it? As Andrew has been saying (I think
more than once), ideally we'd rewrite IOMMU code from scratch. But I
don't see anyone having enough spare time to actually do so ...

Jan

RE: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:49 PM
> 
> While domain_context_mapping() invokes domain_context_unmap() in a
> sub-
> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
> a leak, individual calls to domain_context_mapping_one() aren't
> similarly covered. Such a leak might persist until domain destruction.
> Leverage that these cases can be recognized by pdev being non-NULL.
> 
> Fixes: dec403cc668f ("VT-d: fix iommu_domid for PCI/PCIx devices
> assignment")
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> ---
> The Fixes: tag isn't strictly correct, as error handling had more severe
> shortcomings at the time. But I wouldn't want to blame a commit
> improving error handling to have introduced the leak.
> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1518,7 +1518,12 @@ int domain_context_mapping_one(
>          rc = me_wifi_quirk(domain, bus, devfn, MAP_ME_PHANTOM_FUNC);
> 
>      if ( rc )
> -        domain_context_unmap_one(domain, iommu, bus, devfn);
> +    {
> +        ret = domain_context_unmap_one(domain, iommu, bus, devfn);
> +
> +        if ( !ret && pdev && pdev->devfn == devfn )
> +            check_cleanup_domid_map(domain, pdev, iommu);
> +    }
> 
>      return rc;
>  }

[PATCH 4/6] VT-d: tidy domid map handling

[Jan Beulich]

- Correct struct field type.
- Use unsigned int when that suffices.
- Eliminate a (badly typed) local variable from
  context_set_domain_id().
- Don't use -EFAULT inappropriately.
- Move set_bit() such that it won't be done redundantly.
- Constification.
- Reduce scope of some variables.
- Coding style.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -62,10 +62,10 @@ static struct tasklet vtd_fault_tasklet;
 static int setup_hwdom_device(u8 devfn, struct pci_dev *);
 static void setup_hwdom_rmrr(struct domain *d);
 
-static int domain_iommu_domid(struct domain *d,
-                              struct vtd_iommu *iommu)
+static int domain_iommu_domid(const struct domain *d,
+                              const struct vtd_iommu *iommu)
 {
-    unsigned long nr_dom, i;
+    unsigned int nr_dom, i;
 
     nr_dom = cap_ndoms(iommu->cap);
     i = find_first_bit(iommu->domid_bitmap, nr_dom);
@@ -74,7 +74,7 @@ static int domain_iommu_domid(struct dom
         if ( iommu->domid_map[i] == d->domain_id )
             return i;
 
-        i = find_next_bit(iommu->domid_bitmap, nr_dom, i+1);
+        i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
     }
 
     if ( !d->is_dying )
@@ -88,61 +88,52 @@ static int domain_iommu_domid(struct dom
 #define DID_FIELD_WIDTH 16
 #define DID_HIGH_OFFSET 8
 static int context_set_domain_id(struct context_entry *context,
-                                 struct domain *d,
+                                 const struct domain *d,
                                  struct vtd_iommu *iommu)
 {
-    unsigned long nr_dom, i;
-    int found = 0;
+    unsigned int nr_dom, i;
 
     ASSERT(spin_is_locked(&iommu->lock));
 
     nr_dom = cap_ndoms(iommu->cap);
     i = find_first_bit(iommu->domid_bitmap, nr_dom);
-    while ( i < nr_dom )
-    {
-        if ( iommu->domid_map[i] == d->domain_id )
-        {
-            found = 1;
-            break;
-        }
-        i = find_next_bit(iommu->domid_bitmap, nr_dom, i+1);
-    }
+    while ( i < nr_dom && iommu->domid_map[i] != d->domain_id )
+        i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
 
-    if ( found == 0 )
+    if ( i >= nr_dom )
     {
         i = find_first_zero_bit(iommu->domid_bitmap, nr_dom);
         if ( i >= nr_dom )
         {
             dprintk(XENLOG_ERR VTDPREFIX, "IOMMU: no free domain ids\n");
-            return -EFAULT;
+            return -EBUSY;
         }
         iommu->domid_map[i] = d->domain_id;
+        set_bit(i, iommu->domid_bitmap);
     }
 
-    set_bit(i, iommu->domid_bitmap);
     context->hi |= (i & ((1 << DID_FIELD_WIDTH) - 1)) << DID_HIGH_OFFSET;
     return 0;
 }
 
-static int context_get_domain_id(struct context_entry *context,
-                                 struct vtd_iommu *iommu)
+static int context_get_domain_id(const struct context_entry *context,
+                                 const struct vtd_iommu *iommu)
 {
-    unsigned long dom_index, nr_dom;
     int domid = -1;
 
-    if (iommu && context)
+    if ( iommu && context )
     {
-        nr_dom = cap_ndoms(iommu->cap);
-
-        dom_index = context_domain_id(*context);
+        unsigned int nr_dom = cap_ndoms(iommu->cap);
+        unsigned int dom_index = context_domain_id(*context);
 
         if ( dom_index < nr_dom && iommu->domid_map )
             domid = iommu->domid_map[dom_index];
         else
             dprintk(XENLOG_DEBUG VTDPREFIX,
-                    "dom_index %lu exceeds nr_dom %lu or iommu has no domid_map\n",
+                    "dom_index %u exceeds nr_dom %u or iommu has no domid_map\n",
                     dom_index, nr_dom);
     }
+
     return domid;
 }
 
@@ -1302,7 +1293,7 @@ int __init iommu_alloc(struct acpi_drhd_
     if ( !iommu->domid_bitmap )
         return -ENOMEM;
 
-    iommu->domid_map = xzalloc_array(u16, nr_dom);
+    iommu->domid_map = xzalloc_array(domid_t, nr_dom);
     if ( !iommu->domid_map )
         return -ENOMEM;
 
@@ -1477,11 +1468,12 @@ int domain_context_mapping_one(
         spin_unlock(&hd->arch.mapping_lock);
     }
 
-    if ( context_set_domain_id(context, domain, iommu) )
+    rc = context_set_domain_id(context, domain, iommu);
+    if ( rc )
     {
         spin_unlock(&iommu->lock);
         unmap_vtd_domain_page(context_entries);
-        return -EFAULT;
+        return rc;
     }
 
     context_set_address_width(*context, level_to_agaw(iommu->nr_pt_levels));
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -505,7 +505,7 @@ struct vtd_iommu {
 
     struct list_head ats_devices;
     unsigned long *domid_bitmap;  /* domain id bitmap */
-    u16 *domid_map;               /* domain id mapping array */
+    domid_t *domid_map;           /* domain id mapping array */
     uint32_t version;
 };
 

RE: [PATCH 4/6] VT-d: tidy domid map handling

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:49 PM
> 
> - Correct struct field type.
> - Use unsigned int when that suffices.
> - Eliminate a (badly typed) local variable from
>   context_set_domain_id().
> - Don't use -EFAULT inappropriately.
> - Move set_bit() such that it won't be done redundantly.
> - Constification.
> - Reduce scope of some variables.
> - Coding style.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -62,10 +62,10 @@ static struct tasklet vtd_fault_tasklet;
>  static int setup_hwdom_device(u8 devfn, struct pci_dev *);
>  static void setup_hwdom_rmrr(struct domain *d);
> 
> -static int domain_iommu_domid(struct domain *d,
> -                              struct vtd_iommu *iommu)
> +static int domain_iommu_domid(const struct domain *d,
> +                              const struct vtd_iommu *iommu)
>  {
> -    unsigned long nr_dom, i;
> +    unsigned int nr_dom, i;
> 
>      nr_dom = cap_ndoms(iommu->cap);
>      i = find_first_bit(iommu->domid_bitmap, nr_dom);
> @@ -74,7 +74,7 @@ static int domain_iommu_domid(struct dom
>          if ( iommu->domid_map[i] == d->domain_id )
>              return i;
> 
> -        i = find_next_bit(iommu->domid_bitmap, nr_dom, i+1);
> +        i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
>      }
> 
>      if ( !d->is_dying )
> @@ -88,61 +88,52 @@ static int domain_iommu_domid(struct dom
>  #define DID_FIELD_WIDTH 16
>  #define DID_HIGH_OFFSET 8
>  static int context_set_domain_id(struct context_entry *context,
> -                                 struct domain *d,
> +                                 const struct domain *d,
>                                   struct vtd_iommu *iommu)
>  {
> -    unsigned long nr_dom, i;
> -    int found = 0;
> +    unsigned int nr_dom, i;
> 
>      ASSERT(spin_is_locked(&iommu->lock));
> 
>      nr_dom = cap_ndoms(iommu->cap);
>      i = find_first_bit(iommu->domid_bitmap, nr_dom);
> -    while ( i < nr_dom )
> -    {
> -        if ( iommu->domid_map[i] == d->domain_id )
> -        {
> -            found = 1;
> -            break;
> -        }
> -        i = find_next_bit(iommu->domid_bitmap, nr_dom, i+1);
> -    }
> +    while ( i < nr_dom && iommu->domid_map[i] != d->domain_id )
> +        i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
> 
> -    if ( found == 0 )
> +    if ( i >= nr_dom )
>      {
>          i = find_first_zero_bit(iommu->domid_bitmap, nr_dom);
>          if ( i >= nr_dom )
>          {
>              dprintk(XENLOG_ERR VTDPREFIX, "IOMMU: no free domain ids\n");
> -            return -EFAULT;
> +            return -EBUSY;
>          }
>          iommu->domid_map[i] = d->domain_id;
> +        set_bit(i, iommu->domid_bitmap);
>      }
> 
> -    set_bit(i, iommu->domid_bitmap);
>      context->hi |= (i & ((1 << DID_FIELD_WIDTH) - 1)) << DID_HIGH_OFFSET;
>      return 0;
>  }
> 
> -static int context_get_domain_id(struct context_entry *context,
> -                                 struct vtd_iommu *iommu)
> +static int context_get_domain_id(const struct context_entry *context,
> +                                 const struct vtd_iommu *iommu)
>  {
> -    unsigned long dom_index, nr_dom;
>      int domid = -1;
> 
> -    if (iommu && context)
> +    if ( iommu && context )
>      {
> -        nr_dom = cap_ndoms(iommu->cap);
> -
> -        dom_index = context_domain_id(*context);
> +        unsigned int nr_dom = cap_ndoms(iommu->cap);
> +        unsigned int dom_index = context_domain_id(*context);
> 
>          if ( dom_index < nr_dom && iommu->domid_map )
>              domid = iommu->domid_map[dom_index];
>          else
>              dprintk(XENLOG_DEBUG VTDPREFIX,
> -                    "dom_index %lu exceeds nr_dom %lu or iommu has no
> domid_map\n",
> +                    "dom_index %u exceeds nr_dom %u or iommu has no
> domid_map\n",
>                      dom_index, nr_dom);
>      }
> +
>      return domid;
>  }
> 
> @@ -1302,7 +1293,7 @@ int __init iommu_alloc(struct acpi_drhd_
>      if ( !iommu->domid_bitmap )
>          return -ENOMEM;
> 
> -    iommu->domid_map = xzalloc_array(u16, nr_dom);
> +    iommu->domid_map = xzalloc_array(domid_t, nr_dom);
>      if ( !iommu->domid_map )
>          return -ENOMEM;
> 
> @@ -1477,11 +1468,12 @@ int domain_context_mapping_one(
>          spin_unlock(&hd->arch.mapping_lock);
>      }
> 
> -    if ( context_set_domain_id(context, domain, iommu) )
> +    rc = context_set_domain_id(context, domain, iommu);
> +    if ( rc )
>      {
>          spin_unlock(&iommu->lock);
>          unmap_vtd_domain_page(context_entries);
> -        return -EFAULT;
> +        return rc;
>      }
> 
>      context_set_address_width(*context, level_to_agaw(iommu-
> >nr_pt_levels));
> --- a/xen/drivers/passthrough/vtd/iommu.h
> +++ b/xen/drivers/passthrough/vtd/iommu.h
> @@ -505,7 +505,7 @@ struct vtd_iommu {
> 
>      struct list_head ats_devices;
>      unsigned long *domid_bitmap;  /* domain id bitmap */
> -    u16 *domid_map;               /* domain id mapping array */
> +    domid_t *domid_map;           /* domain id mapping array */
>      uint32_t version;
>  };
> 

[PATCH 5/6] VT-d: introduce helper to convert DID to domid_t

[Jan Beulich]

This is in preparation of adding another "translation" method. Take the
combination of the extra validation both previously open-coded have been
doing: Bounds check and bitmap check. But don't propagate the previous
pointless check of whether ->domid_map[] was actually allocated, as
failure there would lead to overall failure of IOMMU initialization
anyway.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/drivers/passthrough/vtd/extern.h
+++ b/xen/drivers/passthrough/vtd/extern.h
@@ -45,6 +45,8 @@ void disable_intremap(struct vtd_iommu *
 int iommu_alloc(struct acpi_drhd_unit *drhd);
 void iommu_free(struct acpi_drhd_unit *drhd);
 
+domid_t did_to_domain_id(const struct vtd_iommu *iommu, unsigned int did);
+
 int iommu_flush_iec_global(struct vtd_iommu *iommu);
 int iommu_flush_iec_index(struct vtd_iommu *iommu, u8 im, u16 iidx);
 void clear_fault_bits(struct vtd_iommu *iommu);
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -123,15 +123,16 @@ static int context_get_domain_id(const s
 
     if ( iommu && context )
     {
-        unsigned int nr_dom = cap_ndoms(iommu->cap);
         unsigned int dom_index = context_domain_id(*context);
 
-        if ( dom_index < nr_dom && iommu->domid_map )
-            domid = iommu->domid_map[dom_index];
-        else
+        domid = did_to_domain_id(iommu, dom_index);
+        if ( domid == DOMID_INVALID )
+        {
             dprintk(XENLOG_DEBUG VTDPREFIX,
-                    "dom_index %u exceeds nr_dom %u or iommu has no domid_map\n",
-                    dom_index, nr_dom);
+                    "no domid for did %u (nr_dom %u)\n",
+                    dom_index, cap_ndoms(iommu->cap));
+            domid = -1;
+        }
     }
 
     return domid;
@@ -193,6 +194,14 @@ static void check_cleanup_domid_map(stru
     }
 }
 
+domid_t did_to_domain_id(const struct vtd_iommu *iommu, unsigned int did)
+{
+    if ( did >= cap_ndoms(iommu->cap) || !test_bit(did, iommu->domid_bitmap) )
+        return DOMID_INVALID;
+
+    return iommu->domid_map[did];
+}
+
 static void sync_cache(const void *addr, unsigned int size)
 {
     static unsigned long clflush_size = 0;
--- a/xen/drivers/passthrough/vtd/qinval.c
+++ b/xen/drivers/passthrough/vtd/qinval.c
@@ -229,10 +229,7 @@ static int __must_check dev_invalidate_s
     rc = queue_invalidate_wait(iommu, 0, 1, 1, 1);
     if ( rc == -ETIMEDOUT )
     {
-        struct domain *d = NULL;
-
-        if ( test_bit(did, iommu->domid_bitmap) )
-            d = rcu_lock_domain_by_id(iommu->domid_map[did]);
+        struct domain *d = rcu_lock_domain_by_id(did_to_domain_id(iommu, did));
 
         /*
          * In case the domain has been freed or the IOMMU domid bitmap is

RE: [PATCH 5/6] VT-d: introduce helper to convert DID to domid_t

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:50 PM
> 
> This is in preparation of adding another "translation" method. Take the
> combination of the extra validation both previously open-coded have been
> doing: Bounds check and bitmap check. But don't propagate the previous
> pointless check of whether ->domid_map[] was actually allocated, as
> failure there would lead to overall failure of IOMMU initialization
> anyway.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> 
> --- a/xen/drivers/passthrough/vtd/extern.h
> +++ b/xen/drivers/passthrough/vtd/extern.h
> @@ -45,6 +45,8 @@ void disable_intremap(struct vtd_iommu *
>  int iommu_alloc(struct acpi_drhd_unit *drhd);
>  void iommu_free(struct acpi_drhd_unit *drhd);
> 
> +domid_t did_to_domain_id(const struct vtd_iommu *iommu, unsigned int
> did);
> +
>  int iommu_flush_iec_global(struct vtd_iommu *iommu);
>  int iommu_flush_iec_index(struct vtd_iommu *iommu, u8 im, u16 iidx);
>  void clear_fault_bits(struct vtd_iommu *iommu);
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -123,15 +123,16 @@ static int context_get_domain_id(const s
> 
>      if ( iommu && context )
>      {
> -        unsigned int nr_dom = cap_ndoms(iommu->cap);
>          unsigned int dom_index = context_domain_id(*context);
> 
> -        if ( dom_index < nr_dom && iommu->domid_map )
> -            domid = iommu->domid_map[dom_index];
> -        else
> +        domid = did_to_domain_id(iommu, dom_index);
> +        if ( domid == DOMID_INVALID )
> +        {
>              dprintk(XENLOG_DEBUG VTDPREFIX,
> -                    "dom_index %u exceeds nr_dom %u or iommu has no
> domid_map\n",
> -                    dom_index, nr_dom);
> +                    "no domid for did %u (nr_dom %u)\n",
> +                    dom_index, cap_ndoms(iommu->cap));
> +            domid = -1;
> +        }
>      }
> 
>      return domid;
> @@ -193,6 +194,14 @@ static void check_cleanup_domid_map(stru
>      }
>  }
> 
> +domid_t did_to_domain_id(const struct vtd_iommu *iommu, unsigned int
> did)
> +{
> +    if ( did >= cap_ndoms(iommu->cap) || !test_bit(did, iommu-
> >domid_bitmap) )
> +        return DOMID_INVALID;
> +
> +    return iommu->domid_map[did];
> +}
> +
>  static void sync_cache(const void *addr, unsigned int size)
>  {
>      static unsigned long clflush_size = 0;
> --- a/xen/drivers/passthrough/vtd/qinval.c
> +++ b/xen/drivers/passthrough/vtd/qinval.c
> @@ -229,10 +229,7 @@ static int __must_check dev_invalidate_s
>      rc = queue_invalidate_wait(iommu, 0, 1, 1, 1);
>      if ( rc == -ETIMEDOUT )
>      {
> -        struct domain *d = NULL;
> -
> -        if ( test_bit(did, iommu->domid_bitmap) )
> -            d = rcu_lock_domain_by_id(iommu->domid_map[did]);
> +        struct domain *d = rcu_lock_domain_by_id(did_to_domain_id(iommu,
> did));
> 
>          /*
>           * In case the domain has been freed or the IOMMU domid bitmap is

[PATCH 6/6] VT-d: avoid allocating domid_{bit,}map[] when possible

[Jan Beulich]

When an IOMMU implements the full 16 bits worth of DID in context
entries, there's no point going through a memory base translation table.
For IOMMUs not using Caching Mode we can simply use the domain IDs
verbatim, while for Caching Mode we need to avoid DID 0.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
For the case where the memory tables are needed, xvzalloc_array() would
of course be an option to use here as well, despite this being boot time
allocations. Yet the introduction of xvmalloc() et al continues to be
stuck ...

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -62,11 +62,32 @@ static struct tasklet vtd_fault_tasklet;
 static int setup_hwdom_device(u8 devfn, struct pci_dev *);
 static void setup_hwdom_rmrr(struct domain *d);
 
+static bool domid_mapping(const struct vtd_iommu *iommu)
+{
+    return (const void *)iommu->domid_bitmap != (const void *)iommu->domid_map;
+}
+
+static domid_t convert_domid(const struct vtd_iommu *iommu, domid_t domid)
+{
+    /*
+     * While we need to avoid DID 0 for caching-mode IOMMUs, maintain
+     * the property of the transformation being the same in either
+     * direction. By clipping to 16 bits we ensure that the resulting
+     * DID will fit in the respective context entry field.
+     */
+    BUILD_BUG_ON(sizeof(domid_t) > sizeof(uint16_t));
+
+    return !cap_caching_mode(iommu->cap) ? domid : ~domid;
+}
+
 static int domain_iommu_domid(const struct domain *d,
                               const struct vtd_iommu *iommu)
 {
     unsigned int nr_dom, i;
 
+    if ( !domid_mapping(iommu) )
+        return convert_domid(iommu, d->domain_id);
+
     nr_dom = cap_ndoms(iommu->cap);
     i = find_first_bit(iommu->domid_bitmap, nr_dom);
     while ( i < nr_dom )
@@ -91,26 +112,32 @@ static int context_set_domain_id(struct
                                  const struct domain *d,
                                  struct vtd_iommu *iommu)
 {
-    unsigned int nr_dom, i;
+    unsigned int i;
 
     ASSERT(spin_is_locked(&iommu->lock));
 
-    nr_dom = cap_ndoms(iommu->cap);
-    i = find_first_bit(iommu->domid_bitmap, nr_dom);
-    while ( i < nr_dom && iommu->domid_map[i] != d->domain_id )
-        i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
-
-    if ( i >= nr_dom )
+    if ( domid_mapping(iommu) )
     {
-        i = find_first_zero_bit(iommu->domid_bitmap, nr_dom);
+        unsigned int nr_dom = cap_ndoms(iommu->cap);
+
+        i = find_first_bit(iommu->domid_bitmap, nr_dom);
+        while ( i < nr_dom && iommu->domid_map[i] != d->domain_id )
+            i = find_next_bit(iommu->domid_bitmap, nr_dom, i + 1);
+
         if ( i >= nr_dom )
         {
-            dprintk(XENLOG_ERR VTDPREFIX, "IOMMU: no free domain ids\n");
-            return -EBUSY;
+            i = find_first_zero_bit(iommu->domid_bitmap, nr_dom);
+            if ( i >= nr_dom )
+            {
+                dprintk(XENLOG_ERR VTDPREFIX, "IOMMU: no free domain id\n");
+                return -EBUSY;
+            }
+            iommu->domid_map[i] = d->domain_id;
+            set_bit(i, iommu->domid_bitmap);
         }
-        iommu->domid_map[i] = d->domain_id;
-        set_bit(i, iommu->domid_bitmap);
     }
+    else
+        i = convert_domid(iommu, d->domain_id);
 
     context->hi |= (i & ((1 << DID_FIELD_WIDTH) - 1)) << DID_HIGH_OFFSET;
     return 0;
@@ -140,7 +167,12 @@ static int context_get_domain_id(const s
 
 static void cleanup_domid_map(struct domain *domain, struct vtd_iommu *iommu)
 {
-    int iommu_domid = domain_iommu_domid(domain, iommu);
+    int iommu_domid;
+
+    if ( !domid_mapping(iommu) )
+        return;
+
+    iommu_domid = domain_iommu_domid(domain, iommu);
 
     if ( iommu_domid >= 0 )
     {
@@ -196,7 +228,13 @@ static void check_cleanup_domid_map(stru
 
 domid_t did_to_domain_id(const struct vtd_iommu *iommu, unsigned int did)
 {
-    if ( did >= cap_ndoms(iommu->cap) || !test_bit(did, iommu->domid_bitmap) )
+    if ( did >= min(cap_ndoms(iommu->cap), DOMID_MASK + 1) )
+        return DOMID_INVALID;
+
+    if ( !domid_mapping(iommu) )
+        return convert_domid(iommu, did);
+
+    if ( !test_bit(did, iommu->domid_bitmap) )
         return DOMID_INVALID;
 
     return iommu->domid_map[did];
@@ -1296,24 +1334,32 @@ int __init iommu_alloc(struct acpi_drhd_
     if ( !ecap_coherent(iommu->ecap) )
         vtd_ops.sync_cache = sync_cache;
 
-    /* allocate domain id bitmap */
     nr_dom = cap_ndoms(iommu->cap);
-    iommu->domid_bitmap = xzalloc_array(unsigned long, BITS_TO_LONGS(nr_dom));
-    if ( !iommu->domid_bitmap )
-        return -ENOMEM;
 
-    iommu->domid_map = xzalloc_array(domid_t, nr_dom);
-    if ( !iommu->domid_map )
-        return -ENOMEM;
+    if ( nr_dom <= DOMID_MASK + cap_caching_mode(iommu->cap) )
+    {
+        /* Allocate domain id (bit) maps. */
+        iommu->domid_bitmap = xzalloc_array(unsigned long,
+                                            BITS_TO_LONGS(nr_dom));
+        iommu->domid_map = xzalloc_array(domid_t, nr_dom);
+        if ( !iommu->domid_bitmap || !iommu->domid_map )
+            return -ENOMEM;
 
-    /*
-     * If Caching mode is set, then invalid translations are tagged with
-     * domain id 0. Hence reserve bit/slot 0.
-     */
-    if ( cap_caching_mode(iommu->cap) )
+        /*
+         * If Caching mode is set, then invalid translations are tagged
+         * with domain id 0. Hence reserve bit/slot 0.
+         */
+        if ( cap_caching_mode(iommu->cap) )
+        {
+            iommu->domid_map[0] = DOMID_INVALID;
+            __set_bit(0, iommu->domid_bitmap);
+        }
+    }
+    else
     {
-        iommu->domid_map[0] = DOMID_INVALID;
-        __set_bit(0, iommu->domid_bitmap);
+        /* Don't leave dangling NULL pointers. */
+        iommu->domid_bitmap = ZERO_BLOCK_PTR;
+        iommu->domid_map = ZERO_BLOCK_PTR;
     }
 
     return 0;
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -87,7 +87,7 @@
 #define cap_plmr(c)        (((c) >> 5) & 1)
 #define cap_rwbf(c)        (((c) >> 4) & 1)
 #define cap_afl(c)        (((c) >> 3) & 1)
-#define cap_ndoms(c)        (1 << (4 + 2 * ((c) & 0x7)))
+#define cap_ndoms(c)        (1U << (4 + 2 * ((c) & 0x7)))
 
 /*
  * Extended Capability Register

RE: [PATCH 6/6] VT-d: avoid allocating domid_{bit,}map[] when possible

[Tian, Kevin]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 12, 2021 5:50 PM
> 
> When an IOMMU implements the full 16 bits worth of DID in context
> entries, there's no point going through a memory base translation table.
> For IOMMUs not using Caching Mode we can simply use the domain IDs
> verbatim, while for Caching Mode we need to avoid DID 0.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> For the case where the memory tables are needed, xvzalloc_array() would
> of course be an option to use here as well, despite this being boot time
> allocations. Yet the introduction of xvmalloc() et al continues to be
> stuck ...
> 
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -62,11 +62,32 @@ static struct tasklet vtd_fault_tasklet;
>  static int setup_hwdom_device(u8 devfn, struct pci_dev *);
>  static void setup_hwdom_rmrr(struct domain *d);
> 
> +static bool domid_mapping(const struct vtd_iommu *iommu)
> +{
> +    return (const void *)iommu->domid_bitmap != (const void *)iommu-
> >domid_map;
> +}
> +
> +static domid_t convert_domid(const struct vtd_iommu *iommu, domid_t
> domid)
> +{
> +    /*
> +     * While we need to avoid DID 0 for caching-mode IOMMUs, maintain
> +     * the property of the transformation being the same in either
> +     * direction. By clipping to 16 bits we ensure that the resulting
> +     * DID will fit in the respective context entry field.
> +     */
> +    BUILD_BUG_ON(sizeof(domid_t) > sizeof(uint16_t));
> +
> +    return !cap_caching_mode(iommu->cap) ? domid : ~domid;

If DOMID_MASK grows to 0xFFFF (though unlikely), then it translates 
to '0' when caching mode is true. We need extend BUILD_BUG_ON() to 
check DOMID_MASK in this case, since caching mode implies
total_size minus one for available domain IDs 

Thanks
Kevin

Re: [PATCH 6/6] VT-d: avoid allocating domid_{bit,}map[] when possible

[Jan Beulich]

On 15.11.2021 07:18, Tian, Kevin wrote:
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Friday, November 12, 2021 5:50 PM
>>
>> When an IOMMU implements the full 16 bits worth of DID in context
>> entries, there's no point going through a memory base translation table.
>> For IOMMUs not using Caching Mode we can simply use the domain IDs
>> verbatim, while for Caching Mode we need to avoid DID 0.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> For the case where the memory tables are needed, xvzalloc_array() would
>> of course be an option to use here as well, despite this being boot time
>> allocations. Yet the introduction of xvmalloc() et al continues to be
>> stuck ...
>>
>> --- a/xen/drivers/passthrough/vtd/iommu.c
>> +++ b/xen/drivers/passthrough/vtd/iommu.c
>> @@ -62,11 +62,32 @@ static struct tasklet vtd_fault_tasklet;
>>  static int setup_hwdom_device(u8 devfn, struct pci_dev *);
>>  static void setup_hwdom_rmrr(struct domain *d);
>>
>> +static bool domid_mapping(const struct vtd_iommu *iommu)
>> +{
>> +    return (const void *)iommu->domid_bitmap != (const void *)iommu-
>>> domid_map;
>> +}
>> +
>> +static domid_t convert_domid(const struct vtd_iommu *iommu, domid_t
>> domid)
>> +{
>> +    /*
>> +     * While we need to avoid DID 0 for caching-mode IOMMUs, maintain
>> +     * the property of the transformation being the same in either
>> +     * direction. By clipping to 16 bits we ensure that the resulting
>> +     * DID will fit in the respective context entry field.
>> +     */
>> +    BUILD_BUG_ON(sizeof(domid_t) > sizeof(uint16_t));
>> +
>> +    return !cap_caching_mode(iommu->cap) ? domid : ~domid;
> 
> If DOMID_MASK grows to 0xFFFF (though unlikely),

I did consider this too unlikely to warrant taking care of. Now that
you ask for it anyway, ...

> then it translates 
> to '0' when caching mode is true. We need extend BUILD_BUG_ON() to 
> check DOMID_MASK in this case, since caching mode implies
> total_size minus one for available domain IDs 

... I guess I'd rather replace the BUILD_BUG_ON() than extend it or
add a 2nd one.

Jan