Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict mode
From: Yang, Shunyong
Date: Sun Aug 05 2018 - 21:33:05 EST
Hi, Robin,
On 2018/7/26 22:37, Robin Murphy wrote:
> 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@xxxxxxxxxx>
>>>> ---
>>>> 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).
>
When I was reading the code around arm_lpae_split_blk_unmap(), I was
curious in which scenario a block will be split. Now with your comments
"Because DMA code is not the only caller of iommu_map/unmap", it seems
depending on the user.
Would you please explain this further? I mean besides DMA, which user
will use iommu_map/umap and how it split a block.
Thanks.
Shunyong.
>
>>>> {
>>>> 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,
>>>>
>>>
>>> .
>>>
>>
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