From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Leizhen (ThunderTown)" Subject: Re: [PATCH v2 1/1] iommu: Add config option to set lazy mode as default Date: Thu, 28 Mar 2019 14:18:48 +0800 Message-ID: <5C9C6748.8050103@huawei.com> References: <20190327150030.11112-1-thunder.leizhen@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Robin Murphy , Jean-Philippe Brucker , John Garry , Will Deacon , Joerg Roedel , iommu , linux-kernel Cc: Hanjun Guo List-Id: iommu@lists.linux-foundation.org On 2019/3/28 3:18, Robin Murphy wrote: > On 27/03/2019 15:00, Zhen Lei wrote: >> This allows the default behaviour to be controlled by a kernel config >> option instead of changing the command line for the kernel to include >> "iommu.strict=0" on ARM64 where this is desired. >> >> This is similar to CONFIG_IOMMU_DEFAULT_PASSTHROUGH. >> >> Note: At present, intel_iommu, amd_iommu and s390_iommu use lazy mode as >> default, so there is no need to add code for them. > > That seems a bit self-contradictory - if there's a real need for TLB flush behaviour to be statically configurable and not command-line-based then why should users of other architectures be exempt? Yes，you're right. I will make this configuration to be effective for other architectures. BTW, can you give some opinion about below patches? https://patchwork.kernel.org/patch/10857601/ > >> Signed-off-by: Zhen Lei >> --- >> drivers/iommu/Kconfig | 14 ++++++++++++++ >> drivers/iommu/iommu.c | 5 +++++ >> 2 files changed, 19 insertions(+) >> >> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >> index 6f07f3b21816c64..5daa110d0e83a07 100644 >> --- a/drivers/iommu/Kconfig >> +++ b/drivers/iommu/Kconfig >> @@ -85,6 +85,20 @@ config IOMMU_DEFAULT_PASSTHROUGH >> >> If unsure, say N here. >> >> +config IOMMU_DMA_DEFAULT_LAZY_MODE >> + bool "IOMMU DMA use lazy mode to flush IOTLB and free IOVA" >> + depends on IOMMU_API >> + help >> + Support lazy mode, where for every IOMMU DMA unmap operation, the >> + flush operation of IOTLB and the free operation of IOVA are deferred. >> + They are only guaranteed to be done before the related IOVA will be >> + reused. Removing the need to pass in kernel parameters through >> + command line. For example, iommu.strict=0 on ARM64. If this is >> + enabled, you can still disable with kernel parameters, such as >> + iommu.strict=1 depending on the architecture. >> + >> + If unsure, say N here. >> + >> config OF_IOMMU >> def_bool y >> depends on OF && IOMMU_API >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index 33a982e33716369..5acb98e79b5b32d 100644 >> --- a/drivers/iommu/iommu.c >> +++ b/drivers/iommu/iommu.c >> @@ -43,7 +43,12 @@ >> #else >> static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA; >> #endif >> + >> +#ifdef CONFIG_IOMMU_DMA_DEFAULT_LAZY_MODE >> +static bool iommu_dma_strict __read_mostly; >> +#else >> static bool iommu_dma_strict __read_mostly = true; >> +#endif > > For a straightforward boolean, you can simply do: > > static bool foo = IS_ENABLED(CONFIG_FOO); > > but that said, I'm still not particularly convinced that there are a significant number of users in a position to build and install a custom kernel but not edit /etc/default/grub, and who really value the combination of less performance than passthrough with less isolation than strict. > > It's also not necessarily obvious to the user how this interacts with IOMMU_DEFAULT_PASSTHROUGH, so if we really do go down this route, maybe it would be better to refactor the whole lot into a single selection of something like IOMMU_DEFAULT_MODE anyway. > > Robin. > >> >> struct iommu_callback_data { >> const struct iommu_ops *ops; >> -- >> 1.8.3 >> >> > > . > -- Thanks! BestRegards