Re: [PATCH v3 3/7] iommu/mediatek: Use gather to achieve the tlb range flush

From: Robin Murphy
Date: Tue Oct 15 2019 - 07:38:41 EST


On 15/10/2019 06:26, Yong Wu wrote:
On Mon, 2019-10-14 at 15:21 +0100, Robin Murphy wrote:
On 14/10/2019 07:38, Yong Wu wrote:
Use the iommu_gather mechanism to achieve the tlb range flush.
Gather the iova range in the "tlb_add_page", then flush the merged iova
range in iotlb_sync.

Note: If iotlb_sync comes from iommu_iotlb_gather_add_page, we have to
avoid retry the lock since the spinlock have already been acquired.

I think this could probably be even simpler - once the actual
register-poking is all confined to mtk_iommu_tlb_sync(), you should be
able get rid of the per-domain locking in map/unmap and just have a
single per-IOMMU lock to serialise syncs. The io-pgtable code itself
hasn't needed external locking for a while now.

This is more simpler! Thanks very much. I will try this.

The only concern is there is no lock in the iova_to_phys then, maybe use
the new lock instead.

iova_to_phys isn't issuing any syncs, so you don't need any locking there - if anyone calls that in a way which races against the given address being unmapped and remapped they can't expect a meaningful result anyway.

Robin.

Suggested-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
---
1) This is the special case backtrace:

mtk_iommu_iotlb_sync+0x50/0xa0
mtk_iommu_tlb_flush_page_nosync+0x5c/0xd0
__arm_v7s_unmap+0x174/0x598
arm_v7s_unmap+0x30/0x48
mtk_iommu_unmap+0x50/0x78
__iommu_unmap+0xa4/0xf8

2) The checking "if (gather->start == ULONG_MAX) return;" also is
necessary. It will happened when unmap only go to _flush_walk, then
enter this tlb_sync.
---
drivers/iommu/mtk_iommu.c | 29 +++++++++++++++++++++++++----
drivers/iommu/mtk_iommu.h | 1 +
2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index 5f594d6..8712afc 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c
@@ -234,7 +234,12 @@ static void mtk_iommu_tlb_flush_page_nosync(struct iommu_iotlb_gather *gather,
unsigned long iova, size_t granule,
void *cookie)
{
- mtk_iommu_tlb_add_flush_nosync(iova, granule, granule, true, cookie);
+ struct mtk_iommu_data *data = cookie;
+ struct iommu_domain *domain = &data->m4u_dom->domain;
+
+ data->is_in_tlb_gather_add_page = true;
+ iommu_iotlb_gather_add_page(domain, gather, iova, granule);
+ data->is_in_tlb_gather_add_page = false;
}
static const struct iommu_flush_ops mtk_iommu_flush_ops = {
@@ -453,12 +458,28 @@ static void mtk_iommu_flush_iotlb_all(struct iommu_domain *domain)
static void mtk_iommu_iotlb_sync(struct iommu_domain *domain,
struct iommu_iotlb_gather *gather)
{
+ struct mtk_iommu_data *data = mtk_iommu_get_m4u_data();
struct mtk_iommu_domain *dom = to_mtk_domain(domain);
+ bool is_in_gather = data->is_in_tlb_gather_add_page;
+ size_t length = gather->end - gather->start;
unsigned long flags;
- spin_lock_irqsave(&dom->pgtlock, flags);
- mtk_iommu_tlb_sync(mtk_iommu_get_m4u_data());
- spin_unlock_irqrestore(&dom->pgtlock, flags);
+ if (gather->start == ULONG_MAX)
+ return;
+
+ /*
+ * Avoid acquire the lock when it's in gather_add_page since the lock
+ * has already been held.
+ */
+ if (!is_in_gather)
+ spin_lock_irqsave(&dom->pgtlock, flags);
+
+ mtk_iommu_tlb_add_flush_nosync(gather->start, length, gather->pgsize,
+ false, data);
+ mtk_iommu_tlb_sync(data);
+
+ if (!is_in_gather)
+ spin_unlock_irqrestore(&dom->pgtlock, flags);
}
static phys_addr_t mtk_iommu_iova_to_phys(struct iommu_domain *domain,
diff --git a/drivers/iommu/mtk_iommu.h b/drivers/iommu/mtk_iommu.h
index fc0f16e..d29af1d 100644
--- a/drivers/iommu/mtk_iommu.h
+++ b/drivers/iommu/mtk_iommu.h
@@ -58,6 +58,7 @@ struct mtk_iommu_data {
struct iommu_group *m4u_group;
bool enable_4GB;
bool tlb_flush_active;
+ bool is_in_tlb_gather_add_page;
struct iommu_device iommu;
const struct mtk_iommu_plat_data *plat_data;