>From Robin's comment [1] about touching TCR configurations - "TBH if we're going to touch the TCR attributes at all then we should probably correct that sloppiness first - there's an occasional argument for using non-cacheable pagetables even on a coherent SMMU if reducing snoop traffic/latency on walks outweighs the cost of cache maintenance on PTE updates, but anyone thinking they can get that by overriding dma-coherent silently gets the worst of both worlds thanks to this current TCR value." We have IO_PGTABLE_QUIRK_NO_DMA quirk present, but we don't force anybody _not_ using dma-coherent smmu to have non-cacheable page table mappings. Having another quirk flag can help in having non-cacheable memory for page tables once and for all. [1] https://lore.kernel.org/patchwork/patch/1020906/ Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx> --- drivers/iommu/io-pgtable-arm.c | 17 ++++++++++++----- drivers/iommu/io-pgtable.h | 6 ++++++ 2 files changed, 18 insertions(+), 5 deletions(-) diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c index 237cacd4a62b..c76919c30f1a 100644 --- a/drivers/iommu/io-pgtable-arm.c +++ b/drivers/iommu/io-pgtable-arm.c @@ -780,7 +780,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie) struct arm_lpae_io_pgtable *data; if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS | IO_PGTABLE_QUIRK_NO_DMA | - IO_PGTABLE_QUIRK_NON_STRICT)) + IO_PGTABLE_QUIRK_NON_STRICT | + IO_PGTABLE_QUIRK_NON_COHERENT)) return NULL; data = arm_lpae_alloc_pgtable(cfg); @@ -788,9 +789,14 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie) return NULL; /* TCR */ - reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) | - (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT) | - (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT); + reg = ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT; + + if (cfg->quirks & IO_PGTABLE_QUIRK_NON_COHERENT) + reg |= ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_IRGN0_SHIFT | + ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_ORGN0_SHIFT; + else + reg |= ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT | + ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT; switch (ARM_LPAE_GRANULE(data)) { case SZ_4K: @@ -873,7 +879,8 @@ arm_64_lpae_alloc_pgtable_s2(struct io_pgtable_cfg *cfg, void *cookie) /* The NS quirk doesn't apply at stage 2 */ if (cfg->quirks & ~(IO_PGTABLE_QUIRK_NO_DMA | - IO_PGTABLE_QUIRK_NON_STRICT)) + IO_PGTABLE_QUIRK_NON_STRICT | + IO_PGTABLE_QUIRK_NON_COHERENT)) return NULL; data = arm_lpae_alloc_pgtable(cfg); diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h index 47d5ae559329..46604cf7b017 100644 --- a/drivers/iommu/io-pgtable.h +++ b/drivers/iommu/io-pgtable.h @@ -75,6 +75,11 @@ struct io_pgtable_cfg { * IO_PGTABLE_QUIRK_NON_STRICT: Skip issuing synchronous leaf TLBIs * on unmap, for DMA domains using the flush queue mechanism for * delayed invalidation. + * + * IO_PGTABLE_QUIRK_NON_COHERENT: Enforce non-cacheable mappings for + * pagetables even on a coherent SMMU for cases where reducing + * snoop traffic/latency on walks outweighs the cost of cache + * maintenance on PTE updates. */ #define IO_PGTABLE_QUIRK_ARM_NS BIT(0) #define IO_PGTABLE_QUIRK_NO_PERMS BIT(1) @@ -82,6 +87,7 @@ struct io_pgtable_cfg { #define IO_PGTABLE_QUIRK_ARM_MTK_4GB BIT(3) #define IO_PGTABLE_QUIRK_NO_DMA BIT(4) #define IO_PGTABLE_QUIRK_NON_STRICT BIT(5) + #define IO_PGTABLE_QUIRK_NON_COHERENT BIT(6) unsigned long quirks; unsigned long pgsize_bitmap; unsigned int ias; -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
