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    SubjectRe: [PATCH v3 3/7] iommu/mediatek: Use gather to achieve the tlb range flush
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    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@chromium.org>
    >>> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
    >>> ---
    >>> 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;
    >>>
    >
    >

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