linux-kernel - [PATCH v1 8/9] iommu: Introduce iotlb_sync

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Message-ID: <fd1fc335-bd06-d7ac-7839-786957144cf8@gmail.com>
Date:   Fri, 11 May 2018 22:58:59 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>
Cc:     linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1 8/9] iommu: Introduce iotlb_sync_map callback

On 11.05.2018 16:02, Robin Murphy wrote:
> On 08/05/18 19:16, Dmitry Osipenko wrote:
>> Introduce iotlb_sync_map() callback that is invoked in the end of
>> iommu_map(). This new callback allows IOMMU drivers to avoid syncing
>> on mapping of each contiguous chunk and sync only when whole mapping
>> is completed, optimizing performance of the mapping operation.
> 
> This looks like a reasonable compromise - for users of
> IO_PGTABLE_QUIRK_TLBI_ON_MAP we can leave the implicit add_flush() in place for
> each individual map call, but at least move the sync() out to this callback,
> which should still be beneficial overall.
> 
> Modulo one possible nit below,
> 
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> 
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>   drivers/iommu/iommu.c | 8 ++++++--
>>   include/linux/iommu.h | 1 +
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index d2aa23202bb9..39b2ee66aa96 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -1508,13 +1508,14 @@ static size_t iommu_pgsize(struct iommu_domain *domain,
>>   int iommu_map(struct iommu_domain *domain, unsigned long iova,
>>             phys_addr_t paddr, size_t size, int prot)
>>   {
>> +    const struct iommu_ops *ops = domain->ops;
>>       unsigned long orig_iova = iova;
>>       unsigned int min_pagesz;
>>       size_t orig_size = size;
>>       phys_addr_t orig_paddr = paddr;
>>       int ret = 0;
>>   -    if (unlikely(domain->ops->map == NULL ||
>> +    if (unlikely(ops->map == NULL ||
>>                domain->pgsize_bitmap == 0UL))
>>           return -ENODEV;
>>   @@ -1543,7 +1544,7 @@ int iommu_map(struct iommu_domain *domain, unsigned
>> long iova,
>>           pr_debug("mapping: iova 0x%lx pa %pa pgsize 0x%zx\n",
>>                iova, &paddr, pgsize);
>>   -        ret = domain->ops->map(domain, iova, paddr, pgsize, prot);
>> +        ret = ops->map(domain, iova, paddr, pgsize, prot);
>>           if (ret)
>>               break;
>>   @@ -1552,6 +1553,9 @@ int iommu_map(struct iommu_domain *domain, unsigned
>> long iova,
>>           size -= pgsize;
>>       }
>>   +    if (ops->iotlb_sync_map)
>> +        ops->iotlb_sync_map(domain);
> 
> Is it worth trying to skip this in the error case when we're just going to undo
> it immediately?

I can imagine an IOMMU driver that could handle syncing of mapping differently
from the unmapping, in this case it may not worth skipping sync_map in the error
case.