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Message-ID: <5d03ebcb-0cd1-a9ad-0f4e-c219e351396c@arm.com>
Date: Tue, 15 Oct 2019 12:38:35 +0100
From: Robin Murphy <robin.murphy@....com>
To: Yong Wu <yong.wu@...iatek.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>,
Joerg Roedel <joro@...tes.org>,
Will Deacon <will.deacon@....com>,
Evan Green <evgreen@...omium.org>,
Tomasz Figa <tfiga@...gle.com>,
linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
cui.zhang@...iatek.com, chao.hao@...iatek.com,
edison.hsieh@...iatek.com
Subject: Re: [PATCH v3 3/7] iommu/mediatek: Use gather to achieve the tlb
range flush
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@...omium.org>
>>> Signed-off-by: Yong Wu <yong.wu@...iatek.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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