Re: [PATCH v4 1/3] iommu: io-pgtable: add DART pagetable format

["Sven Peter" <sven@svenpeter.dev>]

Hi,

On Tue, Jul 13, 2021, at 21:17, Robin Murphy wrote:
> On 2021-06-27 15:34, 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;
> > +	}
> > +
> >   	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.
> > +	 */
> 
> Nit: I appreciate the effort to document the weirdness, but this comment 
> did rather mislead me initially, and now that I (think I) understand how 
> things work it seems a bit backwards. Could we say something like:
> 
>    "The table format itself always uses two levels, but the total VA
>     space is mapped by four separate tables, making the MMIO registers
>     an effective "level 1". For simplicity, though, we treat this
>     equivalently to LPAE stage 2 concatenation at level 2, with the
>     additional TTBRs each just pointing at consecutive pages."
> 
> ?
> 

Sure, your version is much easier to understand! Thanks.

> > +	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;
> > +	data->pgd_bits += data->bits_per_level;
> > +
> > +	data->pgd = __arm_lpae_alloc_pages(ARM_LPAE_PGD_SIZE(data), GFP_KERNEL,
> > +					   cfg);
> > +	if (!data->pgd)
> > +		goto out_free_data;
> > +
> > +	for (i = 0; i < cfg->apple_dart_cfg.n_ttbrs; ++i)
> > +		cfg->apple_dart_cfg.ttbr[i] =
> > +			virt_to_phys(data->pgd + i * ARM_LPAE_GRANULE(data));
> > +
> > +	return &data->iop;
> > +
> > +out_free_data:
> > +	kfree(data);
> > +	return NULL;
> > +}
> > +
> >   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 +1125,11 @@ struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
> >   	.free	= arm_lpae_free_pgtable,
> >   };
> >   
> > +struct io_pgtable_init_fns io_pgtable_apple_dart_init_fns = {
> > +	.alloc	= apple_dart_alloc_pgtable,
> > +	.free	= arm_lpae_free_pgtable,
> > +};
> > +
> >   #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..fd8e6bd6caf9 100644
> > --- a/drivers/iommu/io-pgtable.c
> > +++ b/drivers/iommu/io-pgtable.c
> > @@ -20,6 +20,7 @@ io_pgtable_init_table[IO_PGTABLE_NUM_FMTS] = {
> >   	[ARM_64_LPAE_S1] = &io_pgtable_arm_64_lpae_s1_init_fns,
> >   	[ARM_64_LPAE_S2] = &io_pgtable_arm_64_lpae_s2_init_fns,
> >   	[ARM_MALI_LPAE] = &io_pgtable_arm_mali_lpae_init_fns,
> > +	[ARM_APPLE_DART] = &io_pgtable_apple_dart_init_fns,
> >   #endif
> >   #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S
> >   	[ARM_V7S] = &io_pgtable_arm_v7s_init_fns,
> > diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> > index 4d40dfa75b55..a4bfac7f85f7 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,
> 
> s/ARM_// - this is pure Apple ;)
> 
> With that fixed and hopefully a somewhat clarified comment above,
> 
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>

True, I'll remove the ARM_ prefix and also change the commit message to match the
subsystem style as mentioned in your reply for the third patch.

Thanks for the review!

> 
> >   	IO_PGTABLE_NUM_FMTS,
> >   };
> >   
> > @@ -136,6 +137,11 @@ struct io_pgtable_cfg {
> >   			u64	transtab;
> >   			u64	memattr;
> >   		} arm_mali_lpae_cfg;
> > +
> > +		struct {
> > +			u64 ttbr[4];
> > +			u32 n_ttbrs;
> > +		} apple_dart_cfg;
> >   	};
> >   };
> >   
> > @@ -246,5 +252,6 @@ 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 */
> > 
> 


Sven

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