Re: [PATCH] s390: PCI: fix IOMMU region init

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 26.09.19 16:10, Matthew Rosato wrote:
> The fix in dbe9cf606c shrinks the IOMMU memory region to a size
> that seems reasonable on the surface, however is actually too
> small as it is based against a 0-mapped address space.  This
> causes breakage with small guests as they can overrun the IOMMU window.
> 
> Let's go back to the prior method of initializing iommu for now.
> 
> Fixes: dbe9cf606c ("s390x/pci: Set the iommu region size mpcifc request")
> Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
> Reported-by: Stefan Zimmerman <stzi@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>

Matt can you also send a patch adding you as the PCI maintainer now
that you have taken over from Collin?



> ---
>  hw/s390x/s390-pci-bus.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> index 963a41c..2d2f4a7 100644
> --- a/hw/s390x/s390-pci-bus.c
> +++ b/hw/s390x/s390-pci-bus.c
> @@ -695,10 +695,15 @@ static const MemoryRegionOps s390_msi_ctrl_ops = {
>  
>  void s390_pci_iommu_enable(S390PCIIOMMU *iommu)
>  {
> +    /*
> +     * The iommu region is initialized against a 0-mapped address space,
> +     * so the smallest IOMMU region we can define runs from 0 to the end
> +     * of the PCI address space.
> +     */
>      char *name = g_strdup_printf("iommu-s390-%04x", iommu->pbdev->uid);
>      memory_region_init_iommu(&iommu->iommu_mr, sizeof(iommu->iommu_mr),
>                               TYPE_S390_IOMMU_MEMORY_REGION, OBJECT(&iommu->mr),
> -                             name, iommu->pal - iommu->pba + 1);
> +                             name, iommu->pal + 1);
>      iommu->enabled = true;
>      memory_region_add_subregion(&iommu->mr, 0, MEMORY_REGION(&iommu->iommu_mr));
>      g_free(name);
>