Re: [PATCH 1/2] iommu/io-pgtable-arm-v7s: Add a quirk to support TTBR up to 35bit for MediaTek

[Miles Chen]

Hi YF,

> The calling to kmem_cache_alloc for level 2 page table allocation may
> run in atomic context, and it fails sometimes when DMA32 zone runs out
> of memory.
> 
> Since Mediatek IOMMU hardware support at most 35bit PA in page table,

s/Mediatek/MediaTek/
s/support/supports/

> so add a quirk to allow the PA of level 2 pgtable support bit35.

35bits PA, right?

>
> 

...snip...

>  
>  	phys = virt_to_phys(table);
> -	if (phys != (arm_v7s_iopte)phys) {
> +	if (phys != (arm_v7s_iopte)phys &&
> +	    !(cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT)) {

I have one question while reading this.

If IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT is set, it means that the phys can be up to 35 bits.
In aarch64, kmalloc() could return up to 52 bits PA (e.g., ARM64_PA_BITS_52=y)

How do we guarantee that phys is safe (<= 35 bits) in this case?
For example:
When IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT is set, the platform guarantees its PAs are at most
35 bits?


Thanks,
Miles
>  		/* Doesn't fit in PTE */
>  		dev_err(dev, "Page table does not fit in PTE: %pa", &phys);
>  		goto out_free;
> @@ -457,9 +464,14 @@ static arm_v7s_iopte arm_v7s_install_table(arm_v7s_iopte *table,
>  					   arm_v7s_iopte curr,
>  					   struct io_pgtable_cfg *cfg)
>  {
> +	phys_addr_t phys = virt_to_phys(table);
>  	arm_v7s_iopte old, new;
>  
> -	new = virt_to_phys(table) | ARM_V7S_PTE_TYPE_TABLE;
> +	new = phys | ARM_V7S_PTE_TYPE_TABLE;
> +
> +	if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT)
> +		new = to_iopte_mtk(phys, new, cfg);
> +
>  	if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_NS)
>  		new |= ARM_V7S_ATTR_NS_TABLE;
>  
> @@ -778,6 +790,7 @@ static phys_addr_t arm_v7s_iova_to_phys(struct io_pgtable_ops *ops,
>  static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
>  						void *cookie)
>  {
> +	slab_flags_t slab_flag = ARM_V7S_TABLE_SLAB_FLAGS;
>  	struct arm_v7s_io_pgtable *data;
>  
>  	if (cfg->ias > (arm_v7s_is_mtk_enabled(cfg) ? 34 : ARM_V7S_ADDR_BITS))
> @@ -788,7 +801,8 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
>  
>  	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>  			    IO_PGTABLE_QUIRK_NO_PERMS |
> -			    IO_PGTABLE_QUIRK_ARM_MTK_EXT))
> +			    IO_PGTABLE_QUIRK_ARM_MTK_EXT |
> +			    IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT))
>  		return NULL;
>  
>  	/* If ARM_MTK_4GB is enabled, the NO_PERMS is also expected. */
> @@ -801,10 +815,12 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg,
>  		return NULL;
>  
>  	spin_lock_init(&data->split_lock);
> +	if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT)
> +		slab_flag = 0;
>  	data->l2_tables = kmem_cache_create("io-pgtable_armv7s_l2",
>  					    ARM_V7S_TABLE_SIZE(2, cfg),
>  					    ARM_V7S_TABLE_SIZE(2, cfg),
> -					    ARM_V7S_TABLE_SLAB_FLAGS, NULL);
> +					    slab_flag, NULL);
>  	if (!data->l2_tables)
>  		goto out_free_data;
>  
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 86af6f0a00a2..7ed15ad4710c 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -74,17 +74,22 @@ struct io_pgtable_cfg {
>  	 *	to support up to 35 bits PA where the bit32, bit33 and bit34 are
>  	 *	encoded in the bit9, bit4 and bit5 of the PTE respectively.
>  	 *
> +	 * IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT: (ARM v7s format) MediaTek IOMMUs
> +	 *	extend the translation table support up to 35 bits PA, the
> +	 *	encoding format is same with IO_PGTABLE_QUIRK_ARM_MTK_EXT.
> +	 *
>  	 * IO_PGTABLE_QUIRK_ARM_TTBR1: (ARM LPAE format) Configure the table
>  	 *	for use in the upper half of a split address space.
>  	 *
>  	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
>  	 *	attributes set in the TCR for a non-coherent page-table walker.
>  	 */
> -	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
> -	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
> -	#define IO_PGTABLE_QUIRK_ARM_MTK_EXT	BIT(3)
> -	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
> -	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
> +	#define IO_PGTABLE_QUIRK_ARM_NS			BIT(0)
> +	#define IO_PGTABLE_QUIRK_NO_PERMS		BIT(1)
> +	#define IO_PGTABLE_QUIRK_ARM_MTK_EXT		BIT(3)
> +	#define IO_PGTABLE_QUIRK_ARM_MTK_TTBR_EXT	BIT(4)
> +	#define IO_PGTABLE_QUIRK_ARM_TTBR1		BIT(5)
> +	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA		BIT(6)
>  	unsigned long			quirks;
>  	unsigned long			pgsize_bitmap;
>  	unsigned int			ias;
> -- 
> 2.18.0
> 
>