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Subject: Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict
 mode
To:     "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Joerg Roedel <joro@8bytes.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        iommu <iommu@lists.linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <1531376312-2192-1-git-send-email-thunder.leizhen@huawei.com>
 <1531376312-2192-5-git-send-email-thunder.leizhen@huawei.com>
 <89cc2201-99ab-3f3b-a2d1-1766515d4375@arm.com> <5B597628.2020103@huawei.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <04239cfa-bcf2-a33a-e662-ebc75e66782b@arm.com>
Date:   Thu, 26 Jul 2018 15:35:59 +0100
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On 2018-07-26 8:20 AM, Leizhen (ThunderTown) wrote:
> On 2018/7/25 6:25, Robin Murphy wrote:
>> On 2018-07-12 7:18 AM, Zhen Lei wrote:
>>> To support the non-strict mode, now we only tlbi and sync for the strict
>>> mode. But for the non-leaf case, always follow strict mode.
>>>
>>> Use the lowest bit of the iova parameter to pass the strict mode:
>>> 0, IOMMU_STRICT;
>>> 1, IOMMU_NON_STRICT;
>>> Treat 0 as IOMMU_STRICT, so that the unmap operation can compatible with
>>> other IOMMUs which still use strict mode.
>>>
>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>> ---
>>>    drivers/iommu/io-pgtable-arm.c | 23 ++++++++++++++---------
>>>    1 file changed, 14 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
>>> index 010a254..9234db3 100644
>>> --- a/drivers/iommu/io-pgtable-arm.c
>>> +++ b/drivers/iommu/io-pgtable-arm.c
>>> @@ -292,7 +292,7 @@ static void __arm_lpae_set_pte(arm_lpae_iopte *ptep, arm_lpae_iopte pte,
>>>      static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>>>                       unsigned long iova, size_t size, int lvl,
>>> -                   arm_lpae_iopte *ptep);
>>> +                   arm_lpae_iopte *ptep, int strict);
>>>      static void __arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
>>>                    phys_addr_t paddr, arm_lpae_iopte prot,
>>> @@ -334,7 +334,7 @@ static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
>>>            size_t sz = ARM_LPAE_BLOCK_SIZE(lvl, data);
>>>              tblp = ptep - ARM_LPAE_LVL_IDX(iova, lvl, data);
>>> -        if (WARN_ON(__arm_lpae_unmap(data, iova, sz, lvl, tblp) != sz))
>>> +        if (WARN_ON(__arm_lpae_unmap(data, iova, sz, lvl, tblp, IOMMU_STRICT) != sz))
>>>                return -EINVAL;
>>>        }
>>>    @@ -531,7 +531,7 @@ static void arm_lpae_free_pgtable(struct io_pgtable *iop)
>>>    static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
>>>                           unsigned long iova, size_t size,
>>>                           arm_lpae_iopte blk_pte, int lvl,
>>> -                       arm_lpae_iopte *ptep)
>>> +                       arm_lpae_iopte *ptep, int strict)
>>
>> DMA code should never ever be splitting blocks anyway, and frankly the TLB maintenance here is dodgy enough (since we can't reasonably do break-before make as VMSA says we should) that I *really* don't want to introduce any possibility of making it more asynchronous. I'd much rather just hard-code the expectation of strict == true for this.
> 
> OK, I will hard-code strict=true for it.
> 
> But since it never ever be happened, why did not give a warning at the beginning?

Because DMA code is not the only caller of iommu_map/unmap. It's 
perfectly legal in the IOMMU API to partially unmap a previous mapping 
such that a block entry needs to be split. The DMA API, however, is a 
lot more constrined, and thus by construction the iommu-dma layer will 
never generate a block-splitting iommu_unmap() except as a result of 
illegal DMA API usage, and we obviously do not need to optimise for that 
(you will get a warning about mismatched unmaps under dma-debug, but 
it's a bit too expensive to police in the general case).

Robin.

>>>    {
>>>        struct io_pgtable_cfg *cfg = &data->iop.cfg;
>>>        arm_lpae_iopte pte, *tablep;
>>> @@ -576,15 +576,18 @@ static size_t arm_lpae_split_blk_unmap(struct arm_lpae_io_pgtable *data,
>>>        }
>>>          if (unmap_idx < 0)
>>> -        return __arm_lpae_unmap(data, iova, size, lvl, tablep);
>>> +        return __arm_lpae_unmap(data, iova, size, lvl, tablep, strict);
>>>          io_pgtable_tlb_add_flush(&data->iop, iova, size, size, true);
>>> +    if (!strict)
>>> +        io_pgtable_tlb_sync(&data->iop);
>>> +
>>>        return size;
>>>    }
>>>      static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>>>                       unsigned long iova, size_t size, int lvl,
>>> -                   arm_lpae_iopte *ptep)
>>> +                   arm_lpae_iopte *ptep, int strict)
>>>    {
>>>        arm_lpae_iopte pte;
>>>        struct io_pgtable *iop = &data->iop;
>>> @@ -609,7 +612,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>>>                io_pgtable_tlb_sync(iop);
>>>                ptep = iopte_deref(pte, data);
>>>                __arm_lpae_free_pgtable(data, lvl + 1, ptep);
>>> -        } else {
>>> +        } else if (strict) {
>>>                io_pgtable_tlb_add_flush(iop, iova, size, size, true);
>>>            }
>>>    @@ -620,25 +623,27 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>>>             * minus the part we want to unmap
>>>             */
>>>            return arm_lpae_split_blk_unmap(data, iova, size, pte,
>>> -                        lvl + 1, ptep);
>>> +                        lvl + 1, ptep, strict);
>>>        }
>>>          /* Keep on walkin' */
>>>        ptep = iopte_deref(pte, data);
>>> -    return __arm_lpae_unmap(data, iova, size, lvl + 1, ptep);
>>> +    return __arm_lpae_unmap(data, iova, size, lvl + 1, ptep, strict);
>>>    }
>>>      static size_t arm_lpae_unmap(struct io_pgtable_ops *ops, unsigned long iova,
>>>                     size_t size)
>>>    {
>>> +    int strict = ((iova & IOMMU_STRICT_MODE_MASK) == IOMMU_STRICT);
>>>        struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
>>>        arm_lpae_iopte *ptep = data->pgd;
>>>        int lvl = ARM_LPAE_START_LVL(data);
>>>    +    iova &= ~IOMMU_STRICT_MODE_MASK;
>>>        if (WARN_ON(iova >= (1ULL << data->iop.cfg.ias)))
>>>            return 0;
>>>    -    return __arm_lpae_unmap(data, iova, size, lvl, ptep);
>>> +    return __arm_lpae_unmap(data, iova, size, lvl, ptep, strict);
>>>    }
>>>      static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
>>>
>>
>> .
>>
>