Re: [PATCH v7 05/11] IOMMU/MMU: propagate IOMMU Device-TLB flush error up to iommu_iotlb_flush{, _all} (top level ones)

["Jan Beulich" <JBeulich@suse.com>]

>>> On 09.06.16 at 14:03, <julien.grall@arm.com> wrote:

> 
> On 09/06/16 12:45, Jan Beulich wrote:
>>>>> On 09.06.16 at 13:12, <julien.grall@arm.com> wrote:
>>> On 08/06/16 09:58, Xu, Quan wrote:
>>>> From: Quan Xu <quan.xu@intel.com>
>>>>
>>>> Signed-off-by: Quan Xu <quan.xu@intel.com>
>>>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>>>>
>>>> CC: Stefano Stabellini <sstabellini@kernel.org>
>>>> CC: Julien Grall <julien.grall@arm.com>
>>>> CC: Jan Beulich <jbeulich@suse.com>
>>>> CC: Kevin Tian <kevin.tian@intel.com>
>>>> ---
>>>>    xen/arch/arm/p2m.c                  |  4 +++-
>>>>    xen/common/memory.c                 | 12 ++++++++++--
>>>>    xen/drivers/passthrough/iommu.c     | 13 +++++++++----
>>>>    xen/drivers/passthrough/x86/iommu.c |  5 +++--
>>>>    xen/include/xen/iommu.h             |  5 +++--
>>>>    5 files changed, 28 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>>>> index 6a19c57..65d8f1a 100644
>>>> --- a/xen/arch/arm/p2m.c
>>>> +++ b/xen/arch/arm/p2m.c
>>>> @@ -1178,7 +1178,9 @@ out:
>>>>        if ( flush )
>>>>        {
>>>>            flush_tlb_domain(d);
>>>> -        iommu_iotlb_flush(d, sgfn, egfn - sgfn);
>>>> +        ret = iommu_iotlb_flush(d, sgfn, egfn - sgfn);
>>>
>>> Sorry for coming late in the discussion. What kind of error do you
>>> expect to return with iommu_tlb_flush?
>>>
>>> Today the ARM SMMU will always return 0 if the TLB flush timeout (see
>>> arm_smmu_tlb_inv_context).
>>>
>>> We may want in the future to return an error when it has timeout,
>>> however only returning an error is not safe at all. The TLB may contain
>>> entries which are invalid (because we remove the mapping earlier) and a
>>> device/domain could take advantage of that.
>>>
>>> So I am not sure if we should let running the guest when a flush has
>>> timeout. Any thoughts?
>>
>> Well, did you look at the rest of this series, and the other dependent
>> one? Guests (other than Dom0) get crashed when a flush times out. I
>> guess that's what you will want on ARM then too.
> 
> I have found a call to domain_crash in iommu_map_page and 
> iommu_unmap_page. However, I have not found any for iommu_tlb_flush.

Perhaps in that other, 3-patch series then?

Jan


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