Re: [PATCH v3 4/6] iommu/io-pgtable-arm: add support for non-strict mode

From: Robin Murphy
Date: Thu Jul 26 2018 - 10:36:05 EST

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:
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).


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,
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);
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,