[PATCH] iommu/amd: flush IOTLB for specific domains only

[Nath, Arindam]

>-----Original Message-----
>From: Daniel Drake [mailto:drake at endlessm.com]
>Sent: Monday, March 27, 2017 5:56 PM
>To: Nath, Arindam
>Cc: joro at 8bytes.org; Deucher, Alexander; Bridgman, John; amd-
>gfx at lists.freedesktop.org; iommu at lists.linux-foundation.org; Suthikulpanit,
>Suravee; Linux Upstreaming Team
>Subject: Re: [PATCH] iommu/amd: flush IOTLB for specific domains only
>
>Hi Arindam,
>
>You CC'd me on this - does this mean that it is a fix for the issue
>described in the thread "amd-iommu: can't boot with amdgpu, AMD-Vi:
>Completion-Wait loop timed out" ?

Yes Daniel, please test this patch to confirm if the issue gets resolved.

Thanks,
Arindam

>
>Thanks
>Daniel
>
>
>On Mon, Mar 27, 2017 at 12:17 AM,  <arindam.nath at amd.com> wrote:
>> From: Arindam Nath <arindam.nath at amd.com>
>>
>> The idea behind flush queues is to defer the IOTLB flushing
>> for domains for which the mappings are no longer valid. We
>> add such domains in queue_add(), and when the queue size
>> reaches FLUSH_QUEUE_SIZE, we perform __queue_flush().
>>
>> Since we have already taken lock before __queue_flush()
>> is called, we need to make sure the IOTLB flushing is
>> performed as quickly as possible.
>>
>> In the current implementation, we perform IOTLB flushing
>> for all domains irrespective of which ones were actually
>> added in the flush queue initially. This can be quite
>> expensive especially for domains for which unmapping is
>> not required at this point of time.
>>
>> This patch makes use of domain information in
>> 'struct flush_queue_entry' to make sure we only flush
>> IOTLBs for domains who need it, skipping others.
>>
>> Signed-off-by: Arindam Nath <arindam.nath at amd.com>
>> ---
>>  drivers/iommu/amd_iommu.c | 15 ++++++++-------
>>  1 file changed, 8 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
>> index 98940d1..6a9a048 100644
>> --- a/drivers/iommu/amd_iommu.c
>> +++ b/drivers/iommu/amd_iommu.c
>> @@ -2227,15 +2227,16 @@ static struct iommu_group
>*amd_iommu_device_group(struct device *dev)
>>
>>  static void __queue_flush(struct flush_queue *queue)
>>  {
>> -       struct protection_domain *domain;
>> -       unsigned long flags;
>>         int idx;
>>
>> -       /* First flush TLB of all known domains */
>> -       spin_lock_irqsave(&amd_iommu_pd_lock, flags);
>> -       list_for_each_entry(domain, &amd_iommu_pd_list, list)
>> -               domain_flush_tlb(domain);
>> -       spin_unlock_irqrestore(&amd_iommu_pd_lock, flags);
>> +       /* First flush TLB of all domains which were added to flush queue */
>> +       for (idx = 0; idx < queue->next; ++idx) {
>> +               struct flush_queue_entry *entry;
>> +
>> +               entry = queue->entries + idx;
>> +
>> +               domain_flush_tlb(&entry->dma_dom->domain);
>> +       }
>>
>>         /* Wait until flushes have completed */
>>         domain_flush_complete(NULL);
>> --
>> 1.9.1
>>