From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FA2FC6FA82 for ; Thu, 22 Sep 2022 14:59:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231738AbiIVO7c (ORCPT ); Thu, 22 Sep 2022 10:59:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41934 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231791AbiIVO7K (ORCPT ); Thu, 22 Sep 2022 10:59:10 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADDA2E4DB5 for ; Thu, 22 Sep 2022 07:59:05 -0700 (PDT) Received: from fraeml745-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4MYJLF3vx3z67NJj; Thu, 22 Sep 2022 22:57:57 +0800 (CST) Received: from lhrpeml500003.china.huawei.com (7.191.162.67) by fraeml745-chm.china.huawei.com (10.206.15.226) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 22 Sep 2022 16:59:03 +0200 Received: from [10.195.244.8] (10.195.244.8) by lhrpeml500003.china.huawei.com (7.191.162.67) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Thu, 22 Sep 2022 15:59:02 +0100 Message-ID: <495de02c-59ce-917f-1cb4-5425a37063ed@huawei.com> Date: Thu, 22 Sep 2022 15:59:01 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v2] iommu: Optimise PCI SAC address trick To: Robin Murphy , CC: , , , Linus Torvalds References: <2b0ca6254dd0102bf559b2a73e9b51da089afbe3.1663764627.git.robin.murphy@arm.com> From: John Garry In-Reply-To: <2b0ca6254dd0102bf559b2a73e9b51da089afbe3.1663764627.git.robin.murphy@arm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.195.244.8] X-ClientProxiedBy: lhrpeml500001.china.huawei.com (7.191.163.213) To lhrpeml500003.china.huawei.com (7.191.162.67) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/09/2022 13:53, Robin Murphy wrote: > Per the reasoning in commit 4bf7fda4dce2 ("iommu/dma: Add config for > PCI SAC address trick") and its subsequent revert, this mechanism no > longer serves its original purpose, but now only works around broken > hardware/drivers in a way that is unfortunately too impactful to remove. > > This does not, however prevent us from solving the performance impact > which that workaround has on large-scale systems that don't need it. > That kicks in once the 32-bit IOVA space fills up and we keep > unsuccessfully trying to allocate from it. However, if we get to that > point then in fact it's already the endgame. The nature of the allocator > is such that the first IOVA we give to a device after the 32-bit space > runs out will be the highest possible address for that device, ever. > If that works, then great, we know we can optimise for speed by always > allocating from the full range. And if it doesn't, then the worst has > already happened and any brokenness is now showing, so there's no point > continuing to try to hide it. > > To that end, implement a flag to refine this into a per-device policy > that can automatically get itself out of the way if and when it stops > being useful. > > CC: Linus Torvalds > Signed-off-by: Robin Murphy FWIW, Reviewed-by: John Garry 2x minor comments below. Thanks, John > --- > > v2: Refactor to avoid CONFIG_IOMMU_DMA=n breakage (oops) > > drivers/iommu/dma-iommu.c | 5 ++++- > drivers/iommu/dma-iommu.h | 8 ++++++++ > drivers/iommu/iommu.c | 3 +++ > include/linux/iommu.h | 2 ++ > 4 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 9297b741f5e8..1cebb16faa33 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -643,9 +643,12 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain, > dma_limit = min(dma_limit, (u64)domain->geometry.aperture_end); > > /* Try to get PCI devices a SAC address */ > - if (dma_limit > DMA_BIT_MASK(32) && !iommu_dma_forcedac && dev_is_pci(dev)) > + if (dma_limit > DMA_BIT_MASK(32) && dev->iommu->pci_workaround) { > iova = alloc_iova_fast(iovad, iova_len, > DMA_BIT_MASK(32) >> shift, false); > + if (!iova) > + dev->iommu->pci_workaround = false; maybe a warn/notice log would be useful for broken systems to give a hint what could have gone wrong when it breaks (if we ever get here). > + } > > if (!iova) > iova = alloc_iova_fast(iovad, iova_len, dma_limit >> shift, > diff --git a/drivers/iommu/dma-iommu.h b/drivers/iommu/dma-iommu.h > index 942790009292..c7be42d4f0cf 100644 > --- a/drivers/iommu/dma-iommu.h > +++ b/drivers/iommu/dma-iommu.h > @@ -17,6 +17,10 @@ int iommu_dma_init_fq(struct iommu_domain *domain); > void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list); > > extern bool iommu_dma_forcedac; > +static inline void iommu_dma_set_pci_workaround(struct device *dev) "pci_workaround" is quite a vague name > +{ > + dev->iommu->pci_workaround = !iommu_dma_forcedac; > +} > > #else /* CONFIG_IOMMU_DMA */ > > @@ -38,5 +42,9 @@ static inline void iommu_dma_get_resv_regions(struct device *dev, struct list_he > { > } > > +static inline void iommu_dma_set_pci_workaround(struct device *dev) > +{ > +} > + > #endif /* CONFIG_IOMMU_DMA */ > #endif /* __DMA_IOMMU_H */ > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index edc768bf8976..ba8afea63ef1 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -323,6 +323,9 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list > > iommu_device_link(iommu_dev, dev); > > + if (dev_is_pci(dev)) > + iommu_dma_set_pci_workaround(dev); > + > return 0; > > out_release: > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 79cb6eb560a8..0eb0f808109c 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -368,6 +368,7 @@ struct iommu_fault_param { > * @fwspec: IOMMU fwspec data > * @iommu_dev: IOMMU device this device is linked to > * @priv: IOMMU Driver private data > + * @pci_workaround: Limit DMA allocations to 32-bit IOVA > * > * TODO: migrate other per device data pointers under iommu_dev_data, e.g. > * struct iommu_group *iommu_group; > @@ -379,6 +380,7 @@ struct dev_iommu { > struct iommu_fwspec *fwspec; > struct iommu_device *iommu_dev; > void *priv; > + bool pci_workaround; > }; > > int iommu_device_register(struct iommu_device *iommu,