From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yong Wu Subject: Re: [PATCH] iommu/mediatek: Move the tlb_sync into tlb_flush Date: Tue, 8 Oct 2019 16:09:28 +0800 Message-ID: <1570522168.19130.39.camel@mhfsdcap03> References: <1569822142-14303-1-git-send-email-yong.wu@mediatek.com> <366b0bda-d874-9109-5c83-ff27301f3486@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <366b0bda-d874-9109-5c83-ff27301f3486@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Robin Murphy Cc: Tomasz Figa , youlin.pei@mediatek.com, anan.sun@mediatek.com, Nicolas Boichat , cui.zhang@mediatek.com, srv_heupstream , Joerg Roedel , Will Deacon , Linux Kernel Mailing List , Evan Green , chao.hao@mediatek.com, "list@263.net:IOMMU DRIVERS" , "moderated list:ARM/Mediatek SoC support" , Matthias Brugger , linux-arm-kernel@lists.infradead.org List-Id: linux-mediatek@lists.infradead.org On Wed, 2019-10-02 at 11:35 +0100, Robin Murphy wrote: > On 02/10/2019 06:18, Tomasz Figa wrote: > > Hi Yong, > > > > On Mon, Sep 30, 2019 at 2:42 PM 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 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). Thanks very much for the confirmation. > > [...] > >> @@ -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). Thanks the hint, At the beginning, I noticed that we don't have DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, thus I thought flush_iotlb_all is unnecessary. After grep, iommu_flush_tlb_all also is called in the x_direct_mapping, then we still need this. If putting it in a new patch(switch flush_iotlb_all to mtk_iommu_tlb_flush_all), then the Fixes tag(commit id: 4d689b619445) is needed? > > Robin. > > _______________________________________________ > Linux-mediatek mailing list > Linux-mediatek@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-mediatek