Re: [PATCH] iommu/vt-d: Flush old iotlb for kdump when the device gets context mapped

[Xunlei Pang <xpang@redhat.com>]

On 2016/11/16 at 22:58, Myron Stowe wrote:
> On Wed, Nov 16, 2016 at 2:13 AM, Xunlei Pang <xpang@redhat.com> wrote:
>> Ccing David
>> On 2016/11/16 at 17:02, Xunlei Pang wrote:
>>> We met the DMAR fault both on hpsa P420i and P421 SmartArray controllers
>>> under kdump, it can be steadily reproduced on several different machines,
>>> the dmesg log is like:
>>> HP HPSA Driver (v 3.4.16-0)
>>> hpsa 0000:02:00.0: using doorbell to reset controller
>>> hpsa 0000:02:00.0: board ready after hard reset.
>>> hpsa 0000:02:00.0: Waiting for controller to respond to no-op
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xe8000 - 0xe8fff]
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xf4000 - 0xf4fff]
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xbdf6e000 - 0xbdf6efff]
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xbdf6f000 - 0xbdf7efff]
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xbdf7f000 - 0xbdf82fff]
>>> DMAR: Setting identity map for device 0000:02:00.0 [0xbdf83000 - 0xbdf84fff]
>>> DMAR: DRHD: handling fault status reg 2
>>> DMAR: [DMA Read] Request device [02:00.0] fault addr fffff000 [fault reason 06] PTE Read access is not set
>>> hpsa 0000:02:00.0: controller message 03:00 timed out
>>> hpsa 0000:02:00.0: no-op failed; re-trying
>>>
>>> After some debugging, we found that the corresponding pte entry value
>>> is correct, and the value of the iommu caching mode is 0, the fault is
>>> probably due to the old iotlb cache of the in-flight DMA.
>>>
>>> Thus need to flush the old iotlb after context mapping is setup for the
>>> device, where the device is supposed to finish reset at its driver probe
>>> stage and no in-flight DMA exists hereafter.
>>>
>>> With this patch, all our problematic machines can survive the kdump tests.
>>>
>>> CC: Myron Stowe <myron.stowe@redhat.com>
>>> CC: Don Brace <don.brace@microsemi.com>
>>> CC: Baoquan He <bhe@redhat.com>
>>> CC: Dave Young <dyoung@redhat.com>
>>> Tested-by: Joseph Szczypek <jszczype@redhat.com>
>>> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
>>> ---
>>>  drivers/iommu/intel-iommu.c | 11 +++++++++--
>>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>>> index 3965e73..eb79288 100644
>>> --- a/drivers/iommu/intel-iommu.c
>>> +++ b/drivers/iommu/intel-iommu.c
>>> @@ -2067,9 +2067,16 @@ static int domain_context_mapping_one(struct dmar_domain *domain,
>>>        * It's a non-present to present mapping. If hardware doesn't cache
>>>        * non-present entry we only need to flush the write-buffer. If the
>>>        * _does_ cache non-present entries, then it does so in the special
> If this does get accepted then we should fix the above grammar also -
>   "If the _does_ cache ..." -> "If the hardware _does_ cache ..."

Yes, but this reminds me of something.
As per the comment, the code here only needs to flush context caches for the special domain 0 which is
used to tag the non-present/erroneous caches, seems we should flush the old domain id of present entries
for kdump according to the analysis, other than the new-allocated domain id. Let me ponder more on this.

Regards,
Xunlei

>
>>> -      * domain #0, which we have to flush:
>>> +      * domain #0, which we have to flush.
>>> +      *
>>> +      * For kdump cases, present entries may be cached due to the in-flight
>>> +      * DMA and copied old pgtable, but there is no unmapping behaviour for
>>> +      * them, so we need an explicit iotlb flush for the newly-mapped device.
>>> +      * For kdump, at this point, the device is supposed to finish reset at
>>> +      * the driver probe stage, no in-flight DMA will exist, thus we do not
>>> +      * need to worry about that anymore hereafter.
>>>        */
>>> -     if (cap_caching_mode(iommu->cap)) {
>>> +     if (is_kdump_kernel() || cap_caching_mode(iommu->cap)) {
>>>               iommu->flush.flush_context(iommu, 0,
>>>                                          (((u16)bus) << 8) | devfn,
>>>                                          DMA_CCMD_MASK_NOBIT,
>> _______________________________________________
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