Re: [PATCH v3 0/4] iommu/amd: Convert the AMD iommu driver to the dma-iommu api
On Mon, Jun 3, 2019 at 11:52 AM Joerg Roedel wrote: > > Hi Tom, > > On Mon, May 06, 2019 at 07:52:02PM +0100, Tom Murphy wrote: > > Convert the AMD iommu driver to the dma-iommu api. Remove the iova > > handling and reserve region code from the AMD iommu driver. > > Thank you for your work on this! I appreciate that much, but I am not > sure we are ready to make that move for the AMD and Intel IOMMU drivers > yet. > > My main concern right now is that these changes will add a per-page > table lock into the fast-path for dma-mapping operations. There has been > much work in the past to remove all locking from these code-paths and > make it scalable on x86. Where is the locking introduced? intel doesn't use a lock in it's iommu_map function: https://github.com/torvalds/linux/blob/f2c7c76c5d0a443053e94adb9f0918fa2fb85c3a/drivers/iommu/intel-iommu.c#L5302 because it cleverly uses cmpxchg64 to avoid using locks: https://github.com/torvalds/linux/blob/f2c7c76c5d0a443053e94adb9f0918fa2fb85c3a/drivers/iommu/intel-iommu.c#L900 And the locking in AMD's iommu_map function can be removed (and i have removed it in my patch set) because it does that same thing as intel: https://github.com/torvalds/linux/blob/f2c7c76c5d0a443053e94adb9f0918fa2fb85c3a/drivers/iommu/amd_iommu.c#L1486 Is there something I'm missing? > > The dma-ops implementations in the x86 IOMMU drivers have the benefit > that they can call their page-table manipulation functions directly and > without locks, because they can make the necessary assumptions. The > IOMMU-API mapping/unmapping path can't make these assumptions because it > is also used for non-DMA-API use-cases. > > So before we can move the AMD and Intel drivers to the generic DMA-API > implementation we need to solve this problem to not introduce new > scalability regressions. > > Regards, > > Joerg > ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v3 0/4] iommu/amd: Convert the AMD iommu driver to the dma-iommu api
Hi Tom, On Mon, May 06, 2019 at 07:52:02PM +0100, Tom Murphy wrote: > Convert the AMD iommu driver to the dma-iommu api. Remove the iova > handling and reserve region code from the AMD iommu driver. Thank you for your work on this! I appreciate that much, but I am not sure we are ready to make that move for the AMD and Intel IOMMU drivers yet. My main concern right now is that these changes will add a per-page table lock into the fast-path for dma-mapping operations. There has been much work in the past to remove all locking from these code-paths and make it scalable on x86. The dma-ops implementations in the x86 IOMMU drivers have the benefit that they can call their page-table manipulation functions directly and without locks, because they can make the necessary assumptions. The IOMMU-API mapping/unmapping path can't make these assumptions because it is also used for non-DMA-API use-cases. So before we can move the AMD and Intel drivers to the generic DMA-API implementation we need to solve this problem to not introduce new scalability regressions. Regards, Joerg ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[PATCH v3 0/4] iommu/amd: Convert the AMD iommu driver to the dma-iommu api
Convert the AMD iommu driver to the dma-iommu api. Remove the iova handling and reserve region code from the AMD iommu driver. Change-log: v3: -rename dma_limit to dma_mask -exit handle_deferred_device early if (!is_kdump_kernel()) -remove pointless calls to handle_deferred_device v2: -Rebase on top of this series: http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-iommu-ops.3 -Add a gfp_t parameter to the iommu_ops::map function. -Made use of the reserve region code inside the dma-iommu api Tom Murphy (4): iommu: Add gfp parameter to iommu_ops::map iommu/dma-iommu: Handle deferred devices iommu/dma-iommu: Use the dev->coherent_dma_mask iommu/amd: Convert the AMD iommu driver to the dma-iommu api drivers/iommu/Kconfig | 1 + drivers/iommu/amd_iommu.c | 694 - drivers/iommu/arm-smmu-v3.c| 2 +- drivers/iommu/arm-smmu.c | 2 +- drivers/iommu/dma-iommu.c | 50 ++- drivers/iommu/exynos-iommu.c | 2 +- drivers/iommu/intel-iommu.c| 2 +- drivers/iommu/iommu.c | 43 +- drivers/iommu/ipmmu-vmsa.c | 2 +- drivers/iommu/msm_iommu.c | 2 +- drivers/iommu/mtk_iommu.c | 2 +- drivers/iommu/mtk_iommu_v1.c | 2 +- drivers/iommu/omap-iommu.c | 2 +- drivers/iommu/qcom_iommu.c | 2 +- drivers/iommu/rockchip-iommu.c | 2 +- drivers/iommu/s390-iommu.c | 2 +- drivers/iommu/tegra-gart.c | 2 +- drivers/iommu/tegra-smmu.c | 2 +- include/linux/iommu.h | 21 +- 19 files changed, 184 insertions(+), 653 deletions(-) -- 2.17.1 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu