Messages in this thread | | | Subject | Re: [PATCH] iommu/mediatek: Move the tlb_sync into tlb_flush | From | Robin Murphy <> | Date | Wed, 2 Oct 2019 11:35:16 +0100 |
| |
On 02/10/2019 06:18, Tomasz Figa wrote: > Hi Yong, > > On Mon, Sep 30, 2019 at 2:42 PM Yong Wu <yong.wu@mediatek.com> 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 dom->pgtlock, then it will cause the variable >> "tlb_flush_active" may be changed unexpectedly, we could see this warning >> log randomly: >> > > Thanks for the patch! Please see my comments inline. > >> mtk-iommu 10205000.iommu: Partial TLB flush timed out, falling back to >> full flush >> >> To fix this issue, we can add dom->pgtlock in the "mtk_iommu_iotlb_sync". >> And when checking this issue, we find that __arm_v7s_unmap call >> io_pgtable_tlb_add_flush consecutively when it is supersection/largepage, >> this also is potential unsafe for us. There is no tlb flush queue in the >> MediaTek M4U HW. The HW always expect the tlb_flush/tlb_sync one by one. >> If v7s don't always gurarantee the sequence, Thus, In this patch I move >> the tlb_sync into tlb_flush(also rename the function deleting "_nosync"). >> and we don't care if it is leaf, rearrange the callback functions. Also, >> the tlb flush/sync was already finished in v7s, then iotlb_sync and >> iotlb_sync_all is unnecessary. > > Performance-wise, we could do much better. Instead of synchronously > syncing at the end of mtk_iommu_tlb_add_flush(), we could sync at the > beginning, if there was any previous flush still pending. We would > also have to keep the .iotlb_sync() callback, to take care of waiting > for the last flush. That would allow better pipelining with CPU in > cases like this: > > for (all pages in range) { > change page table(); > flush(); > } > > "change page table()" could execute while the IOMMU is flushing the > previous change.
FWIW, given that the underlying invalidation mechanism is range-based, this driver would be an ideal candidate for making use of the new iommu_gather mechanism. As a fix for stable, though, simply ensuring that add_flush syncs any pending invalidation before issuing a new one sounds like a good idea (and probably a simpler patch too).
[...] >> @@ -574,8 +539,7 @@ static int mtk_iommu_of_xlate(struct device *dev, struct of_phandle_args *args) >> .detach_dev = mtk_iommu_detach_device, >> .map = mtk_iommu_map, >> .unmap = mtk_iommu_unmap, >> - .flush_iotlb_all = mtk_iommu_flush_iotlb_all, > > Don't we still want .flush_iotlb_all()? I think it should be more > efficient in some cases than doing a big number of single flushes. > (That said, the previous implementation didn't do any flush at all. It > just waited for previously queued flushes to happen. Was that > expected?)
Commit 07fdef34d2be ("iommu/arm-smmu-v3: Implement flush_iotlb_all hook") has an explanation of what the deal was there - similarly, it's probably worth this driver implementing it properly as well now (but that's really a separate patch).
Robin.
| |