Re: [PATCH v4 2/7] iommu/mediatek: Add a new tlb_lock for tlb_flush

[Will Deacon]

On Wed, Oct 16, 2019 at 11:33:07AM +0800, Yong Wu wrote:
> The commit 4d689b619445 ("iommu/io-pgtable-arm-v7s: Convert to IOMMU API
> TLB sync") help move the tlb_sync of unmap from v7s into the iommu
> framework. It helps add a new function "mtk_iommu_iotlb_sync", But it
> lacked the lock, then it will cause the variable "tlb_flush_active"
> may be changed unexpectedly, we could see this warning log randomly:
> 
> mtk-iommu 10205000.iommu: Partial TLB flush timed out, falling back to
> full flush
> 
> The HW requires tlb_flush/tlb_sync in pairs strictly, this patch adds
> a new tlb_lock for tlb operations to fix this issue.
> 
> Fixes: 4d689b619445 ("iommu/io-pgtable-arm-v7s: Convert to IOMMU API TLB
> sync")
> Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> ---
>  drivers/iommu/mtk_iommu.c | 23 ++++++++++++++++++++++-
>  drivers/iommu/mtk_iommu.h |  1 +
>  2 files changed, 23 insertions(+), 1 deletion(-)

[...]

>  static void mtk_iommu_tlb_flush_page_nosync(struct iommu_iotlb_gather *gather,
>  					    unsigned long iova, size_t granule,
>  					    void *cookie)
>  {
> +	struct mtk_iommu_data *data = cookie;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&data->tlb_lock, flags);
>  	mtk_iommu_tlb_add_flush_nosync(iova, granule, granule, true, cookie);
> +	spin_unlock_irqrestore(&data->tlb_lock, flags);

Given that you release the lock here, what prevents another nosync()
operation being issued before you've managed to do the sync()?

Will