Re: [PATCH 1/3] iommu: io-pgtable: add DART pagetable format

Robin Murphy
2021-03-24T16:38:59Z

On 2021-03-20 15:19, Sven Peter wrote:
> Apple's DART iommu uses a pagetable format that's very similar to the ones
> already implemented by io-pgtable.c.
> Add a new format variant to support the required differences.

TBH there look to be more differences than similarities, but I guess we
already opened that door with the Mali format, and nobody likes writing
pagetable code :)

> Signed-off-by: Sven Peter <sven@svenpeter.dev>
> ---
> drivers/iommu/Kconfig | 13 +++++++
> drivers/iommu/io-pgtable-arm.c | 70 ++++++++++++++++++++++++++++++++++
> drivers/iommu/io-pgtable.c | 3 ++
> include/linux/io-pgtable.h | 6 +++
> 4 files changed, 92 insertions(+)
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 192ef8f61310..3c95c8524abe 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -39,6 +39,19 @@ config IOMMU_IO_PGTABLE_LPAE
> sizes at both stage-1 and stage-2, as well as address spaces
> up to 48-bits in size.
>
> +config IOMMU_IO_PGTABLE_APPLE_DART

Does this really need to be configurable? I don't think there's an
appreciable code saving to be had, and it's not like we do it for any of
the other sub-formats.

> + bool "Apple DART Descriptor Format"
> + select IOMMU_IO_PGTABLE
> + select IOMMU_IO_PGTABLE_LPAE
> + depends on ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
> + help
> + Enable support for the Apple DART iommu pagetable format.
> + This format is a variant of the ARMv7/v8 Long Descriptor
> + Format specific to Apple's iommu found in their SoCs.
> +
> + Say Y here if you have a Apple SoC like the M1 which
> + contains DART iommus.
> +
> config IOMMU_IO_PGTABLE_LPAE_SELFTEST
> bool "LPAE selftests"
> depends on IOMMU_IO_PGTABLE_LPAE
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 87def58e79b5..18674469313d 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -127,6 +127,10 @@
> #define ARM_MALI_LPAE_MEMATTR_IMP_DEF 0x88ULL
> #define ARM_MALI_LPAE_MEMATTR_WRITE_ALLOC 0x8DULL
>
> +/* APPLE_DART_PTE_PROT_NO_WRITE actually maps to ARM_LPAE_PTE_AP_RDONLY */
> +#define APPLE_DART_PTE_PROT_NO_WRITE (1<<7)
Given that there's apparently zero similarity with any of the other
attributes/permissions, this seems more like a coincidence that probably
doesn't need to be called out.

> +#define APPLE_DART_PTE_PROT_NO_READ (1<<8)
> +

Do you have XN permission? How about memory type attributes?

> /* IOPTE accessors */
> #define iopte_deref(pte,d) __va(iopte_to_paddr(pte, d))
>
> @@ -381,6 +385,17 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct arm_lpae_io_pgtable *data,
> {
> arm_lpae_iopte pte;
>
> +#ifdef CONFIG_IOMMU_IO_PGTABLE_APPLE_DART

As a general tip, prefer IS_ENABLED() to inline #ifdefs.

> + 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;
> + }
> +#endif
> +
> if (data->iop.fmt == ARM_64_LPAE_S1 ||
> data->iop.fmt == ARM_32_LPAE_S1) {
> pte = ARM_LPAE_PTE_nG;
> @@ -1043,6 +1058,54 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> return NULL;
> }
>
> +#ifdef CONFIG_IOMMU_IO_PGTABLE_APPLE_DART

Similarly, prefer __maybe_unused rather than #ifdefing functions if they
don't contain any config-dependent references.

> +static struct io_pgtable *
> +apple_dart_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie)
> +{
> + struct arm_lpae_io_pgtable *data;
> +
> + if (cfg->ias > 38)
> + return NULL;
> + if (cfg->oas > 36)
> + return NULL;
> +
> + if (!cfg->coherent_walk)
> + return NULL;

For completeness you should probably also reject any quirks, since none
of them are applicable either.

> +
> + cfg->pgsize_bitmap &= SZ_16K;

No block mappings?

> + if (!cfg->pgsize_bitmap)
> + return NULL;
> +
> + data = arm_lpae_alloc_pgtable(cfg);
> + if (!data)
> + return NULL;
> +
> + /*
> + * the hardware only supports this specific three level pagetable layout with
> + * the first level being encoded into four hardware registers
> + */
> + data->start_level = ARM_LPAE_MAX_LEVELS - 2;

The comment implies that walks should start at level 1 (for a 3-level
table), but the code here says (in an unnecessarily roundabout manner)
level 2 :/

Which is it?

> + data->pgd_bits = 13;

What if ias < 38? Couldn't we get away with only allocating as much as
we actually need?

> + data->bits_per_level = 11;
> +
> + data->pgd = __arm_lpae_alloc_pages(ARM_LPAE_PGD_SIZE(data), GFP_KERNEL,
> + cfg);
> + if (!data->pgd)
> + goto out_free_data;
> +
> + cfg->apple_dart_cfg.pgd[0] = virt_to_phys(data->pgd);
> + cfg->apple_dart_cfg.pgd[1] = virt_to_phys(data->pgd + 0x4000);
> + cfg->apple_dart_cfg.pgd[2] = virt_to_phys(data->pgd + 0x8000);
> + cfg->apple_dart_cfg.pgd[3] = virt_to_phys(data->pgd + 0xc000);
> +
> + return &data->iop;
> +
> +out_free_data:
> + kfree(data);
> + return NULL;
> +}
> +#endif
> +
> struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s1_init_fns = {
> .alloc = arm_64_lpae_alloc_pgtable_s1,
> .free = arm_lpae_free_pgtable,
> @@ -1068,6 +1131,13 @@ struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
> .free = arm_lpae_free_pgtable,
> };
>
> +#ifdef CONFIG_IOMMU_IO_PGTABLE_APPLE_DART
> +struct io_pgtable_init_fns io_pgtable_apple_dart_init_fns = {
> + .alloc = apple_dart_alloc_pgtable,
> + .free = arm_lpae_free_pgtable,
> +};
> +#endif
> +
> #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>
> static struct io_pgtable_cfg *cfg_cookie __initdata;
> diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
> index 6e9917ce980f..d86590b0673a 100644
> --- a/drivers/iommu/io-pgtable.c
> +++ b/drivers/iommu/io-pgtable.c
> @@ -27,6 +27,9 @@ io_pgtable_init_table[IO_PGTABLE_NUM_FMTS] = {
> #ifdef CONFIG_AMD_IOMMU
> [AMD_IOMMU_V1] = &io_pgtable_amd_iommu_v1_init_fns,
> #endif
> +#ifdef CONFIG_IOMMU_IO_PGTABLE_APPLE_DART
> + [ARM_APPLE_DART] = &io_pgtable_apple_dart_init_fns,
> +#endif
> };
>
> struct io_pgtable_ops *alloc_io_pgtable_ops(enum io_pgtable_fmt fmt,
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index a4c9ca2c31f1..19d9b631d319 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -16,6 +16,7 @@ enum io_pgtable_fmt {
> ARM_V7S,
> ARM_MALI_LPAE,
> AMD_IOMMU_V1,
> + ARM_APPLE_DART,
> IO_PGTABLE_NUM_FMTS,
> };
>
> @@ -136,6 +137,10 @@ struct io_pgtable_cfg {
> u64 transtab;
> u64 memattr;
> } arm_mali_lpae_cfg;
> +
> + struct {
> + u64 pgd[4];

Nit: in the driver you call the registers "TTBR" rather than "PGD". The
config here tries to represent hardware/architecture definitions rather
than internal abstractions.

Robin.

> + } apple_dart_cfg;
> };
> };
>
> @@ -250,5 +255,6 @@ extern struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns;
> extern struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns;
> extern struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns;
> extern struct io_pgtable_init_fns io_pgtable_amd_iommu_v1_init_fns;
> +extern struct io_pgtable_init_fns io_pgtable_apple_dart_init_fns;
>
> #endif /* __IO_PGTABLE_H */
> --
> 2.25.1
>
>