Re: [Xen-devel] [RFC PATCH 4/9] xen/arm: p2m: Update IOMMU mapping whenever possible if page table is not shared

[Julien Grall <julien.grall@xxxxxxx>]

Hi Oleksandr,

On 21/04/17 19:44, Oleksandr Tyshchenko wrote:
> On Fri, Apr 21, 2017 at 7:27 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > On 21/04/17 15:18, Oleksandr Tyshchenko wrote:
> > > On Wed, Apr 19, 2017 at 8:46 PM, Julien Grall <julien.grall@xxxxxxx>
> > > wrote:
> Aha. Seems, I understand what you meant. I already have a check in IPMMU driver:
>
> /*
> * both the virtual address and the physical one, as well as
> * the size of the mapping, must be aligned (at least) to the
> * size of the smallest page supported by the hardware
> */
> if (!IS_ALIGNED(iova | paddr | size, min_pagesz)) {
> printk("unaligned: iova 0x%lx pa 0x%"PRIx64" size 0x%zx min_pagesz 0x%x\n",
>       iova, paddr, size, min_pagesz);
> return -EINVAL;
> }
>
> where min_pagesz - is a minimum page size supported by hardware.
> Hope, that this check can catch such case.
I think will cover what I meant. Although, can't we do this check when 
the IOMMU is initialized at boot time rather than for every mapping?
For instance you know that if the mimimum page granularity supported  by 
the IOMMU is bigger than PAGE_SIZE, than you will likely get into 
trouble later on.
So rather than randomly crashing at runtime, you can disable the 
IOMMU/panic at boot time.
Cheers,

--
Julien Grall

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