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

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;
>       }
>   }

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