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SubjectRe: [PATCH v4 1/3] iommu: io-pgtable: add DART pagetable format
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On 27.06.21 16:34, Sven Peter wrote:
>
> Apple's DART iommu uses a pagetable format that shares some
> similarities with the ones already implemented by io-pgtable.c.
> Add a new format variant to support the required differences
> so that we don't have to duplicate the pagetable handling code.
>
> Signed-off-by: Sven Peter <sven@svenpeter.dev>
> ---
> drivers/iommu/io-pgtable-arm.c | 62 ++++++++++++++++++++++++++++++++++
> drivers/iommu/io-pgtable.c | 1 +
> include/linux/io-pgtable.h | 7 ++++
> 3 files changed, 70 insertions(+)
>
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 87def58e79b5..1dd5c45b4b5b 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -127,6 +127,9 @@
> #define ARM_MALI_LPAE_MEMATTR_IMP_DEF 0x88ULL
> #define ARM_MALI_LPAE_MEMATTR_WRITE_ALLOC 0x8DULL
>
> +#define APPLE_DART_PTE_PROT_NO_WRITE (1<<7)
> +#define APPLE_DART_PTE_PROT_NO_READ (1<<8)
> +
> /* IOPTE accessors */
> #define iopte_deref(pte,d) __va(iopte_to_paddr(pte, d))
>
> @@ -381,6 +384,15 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct arm_lpae_io_pgtable *data,
> {
> arm_lpae_iopte pte;
>
> + if (data->iop.fmt == ARM_APPLE_DART) {
> + pte = 0;
> + if (!(prot & IOMMU_WRITE))
> + pte |= APPLE_DART_PTE_PROT_NO_WRITE;
> + if (!(prot & IOMMU_READ))
> + pte |= APPLE_DART_PTE_PROT_NO_READ;
> + return pte;

What about the other bits, such as sharability, XN, etc? Do they not
exist on DART? Or have they not been reverse engineered and 0s happen to
"just work"?

> + }
> +
> if (data->iop.fmt == ARM_64_LPAE_S1 ||
> data->iop.fmt == ARM_32_LPAE_S1) {
> pte = ARM_LPAE_PTE_nG;
> @@ -1043,6 +1055,51 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> return NULL;
> }
>
> +static struct io_pgtable *
> +apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> +{
> + struct arm_lpae_io_pgtable *data;
> + int i;
> +
> + if (cfg->oas > 36)
> + return NULL;
> +
> + data = arm_lpae_alloc_pgtable(cfg);
> + if (!data)
> + return NULL;
> +
> + /*
> + * Apple's DART always requires three levels with the first level being
> + * stored in four MMIO registers. We always concatenate the first and
> + * second level so that we only have to setup the MMIO registers once.
> + * This results in an effective two level pagetable.
> + */
> + if (data->start_level < 1)
> + return NULL;
> + if (data->start_level == 1 && data->pgd_bits > 2)
> + return NULL;
> + if (data->start_level > 1)
> + data->pgd_bits = 0;
> + data->start_level = 2;
> + cfg->apple_dart_cfg.n_ttbrs = 1 << data->pgd_bits;

Maybe add a BUG_ON if n_ttbrs > ARRAY_SIZE(ttbr)? Or alternatively, do a
normal runtime check and bail out then.


Alex



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