[PATCH v2 0/2] s390x/pci: small set of fixes

[PATCH v2 0/2] s390x/pci: small set of fixes

[Matthew Rosato]

The following set of changes are associated with issues exposed by testing
of the 'vfio: Adopt iommufd' series.

The first patch fixes an existing assumption that a vfio device will always
have a group fd (which is no longer true if cdev is used, which can only
happen once the iommufd backend is used).  This patch really only needs to
go into 8.2 if the 'vfio: Adopt iommufd' series does (but would be fine to 
go into 8.2 without it too).

The second patch fixes an issue where we do not detect that a vfio DMA limit
was never read from vfio.  This is actually an existing bug as it's possible
for an older host kernel to be missing this support today; so ideally this one
should be targeted for 8.2 regardless. 

Changes for v2:
- minor style changes (Phil, Thomas)

Matthew Rosato (2):
  s390x/pci: bypass vfio DMA counting when using cdev
  s390x/pci: only limit DMA aperture if vfio DMA limit reported

 hw/s390x/s390-pci-vfio.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.41.0

[PATCH v2 1/2] s390x/pci: bypass vfio DMA counting when using cdev

[Matthew Rosato]

The current code assumes that there is always a vfio group, but
that's no longer guaranteed with the iommufd backend when using
cdev.  In this case, we don't need to track the vfio dma limit
anyway.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 hw/s390x/s390-pci-vfio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
index 59a2e03873..e28573b593 100644
--- a/hw/s390x/s390-pci-vfio.c
+++ b/hw/s390x/s390-pci-vfio.c
@@ -66,6 +66,10 @@ S390PCIDMACount *s390_pci_start_dma_count(S390pciState *s,
 
     assert(vpdev);
 
+    if (!vpdev->vbasedev.group) {
+        return NULL;
+    }
+
     id = vpdev->vbasedev.group->container->fd;
 
     if (!s390_pci_update_dma_avail(id, &avail)) {
-- 
2.41.0

[PATCH v2 2/2] s390x/pci: only limit DMA aperture if vfio DMA limit reported

[Matthew Rosato]

If the host kernel lacks vfio DMA limit reporting, do not attempt
to shrink the guest DMA aperture.

Fixes: df202e3ff3 ("s390x/pci: shrink DMA aperture to be bound by vfio DMA limit")
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 hw/s390x/s390-pci-vfio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
index e28573b593..7dbbc76823 100644
--- a/hw/s390x/s390-pci-vfio.c
+++ b/hw/s390x/s390-pci-vfio.c
@@ -136,7 +136,7 @@ static void s390_pci_read_base(S390PCIBusDevice *pbdev,
      * to the guest based upon the vfio DMA limit.
      */
     vfio_size = pbdev->iommu->max_dma_limit << TARGET_PAGE_BITS;
-    if (vfio_size < (cap->end_dma - cap->start_dma + 1)) {
+    if (vfio_size > 0 && vfio_size < cap->end_dma - cap->start_dma + 1) {
         pbdev->zpci_fn.edma = cap->start_dma + vfio_size - 1;
     }
 }
-- 
2.41.0

Re: [PATCH v2 0/2] s390x/pci: small set of fixes

[Thomas Huth]

On 10/11/2023 18.51, Matthew Rosato wrote:
> The following set of changes are associated with issues exposed by testing
> of the 'vfio: Adopt iommufd' series.
> 
> The first patch fixes an existing assumption that a vfio device will always
> have a group fd (which is no longer true if cdev is used, which can only
> happen once the iommufd backend is used).  This patch really only needs to
> go into 8.2 if the 'vfio: Adopt iommufd' series does (but would be fine to
> go into 8.2 without it too).
> 
> The second patch fixes an issue where we do not detect that a vfio DMA limit
> was never read from vfio.  This is actually an existing bug as it's possible
> for an older host kernel to be missing this support today; so ideally this one
> should be targeted for 8.2 regardless.
> 
> Changes for v2:
> - minor style changes (Phil, Thomas)
> 
> Matthew Rosato (2):
>    s390x/pci: bypass vfio DMA counting when using cdev
>    s390x/pci: only limit DMA aperture if vfio DMA limit reported
> 
>   hw/s390x/s390-pci-vfio.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)

Thank you, queued them now!

  Thomas

Re: [PATCH v2 0/2] s390x/pci: small set of fixes

[Eric Farman]

On Fri, 2023-11-10 at 12:51 -0500, Matthew Rosato wrote:
> The following set of changes are associated with issues exposed by
> testing
> of the 'vfio: Adopt iommufd' series.

...snip...

> Matthew Rosato (2):
>   s390x/pci: bypass vfio DMA counting when using cdev
>   s390x/pci: only limit DMA aperture if vfio DMA limit reported
> 
>  hw/s390x/s390-pci-vfio.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 

Apologies for missing v1 while I was out, but FWIW, for the series:

Reviewed-by: Eric Farman <farman@linux.ibm.com>

Re: [PATCH v2 2/2] s390x/pci: only limit DMA aperture if vfio DMA limit reported

[Michael Tokarev]

10.11.2023 20:51, Matthew Rosato wrote:
> If the host kernel lacks vfio DMA limit reporting, do not attempt
> to shrink the guest DMA aperture.
> 
> Fixes: df202e3ff3 ("s390x/pci: shrink DMA aperture to be bound by vfio DMA limit")
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>

Is this stable-8.1 material?

Thanks,

/mjt

> ---
>   hw/s390x/s390-pci-vfio.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
> index e28573b593..7dbbc76823 100644
> --- a/hw/s390x/s390-pci-vfio.c
> +++ b/hw/s390x/s390-pci-vfio.c
> @@ -136,7 +136,7 @@ static void s390_pci_read_base(S390PCIBusDevice *pbdev,
>        * to the guest based upon the vfio DMA limit.
>        */
>       vfio_size = pbdev->iommu->max_dma_limit << TARGET_PAGE_BITS;
> -    if (vfio_size < (cap->end_dma - cap->start_dma + 1)) {
> +    if (vfio_size > 0 && vfio_size < cap->end_dma - cap->start_dma + 1) {
>           pbdev->zpci_fn.edma = cap->start_dma + vfio_size - 1;
>       }
>   }

Re: [PATCH v2 2/2] s390x/pci: only limit DMA aperture if vfio DMA limit reported

[Matthew Rosato]

On 11/13/23 4:24 PM, Michael Tokarev wrote:
> 10.11.2023 20:51, Matthew Rosato wrote:
>> If the host kernel lacks vfio DMA limit reporting, do not attempt
>> to shrink the guest DMA aperture.
>>
>> Fixes: df202e3ff3 ("s390x/pci: shrink DMA aperture to be bound by vfio DMA limit")
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> 
> Is this stable-8.1 material?
> 
> Thanks,
> 
> /mjt
> 

Yes, I believe it is (sorry, should have added CC stable)

If you have a host kernel that doesn't report the vfio DMA limit the resulting PCI device will be rendered unusable in the s390x guest due this bug.

Thanks,
Matt