Messages in this thread | | | Subject | Re: [PATCH v2 1/1] iommu: Add config option to set lazy mode as default | From | Robin Murphy <> | Date | Wed, 27 Mar 2019 19:18:51 +0000 |
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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?
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > --- > 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 > >
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