Subject: [PATCH 4/3] iommu/io-pgtable: Rationalise quirk handling

From: [email-masked] (Robin Murphy)
Date: Fri, 12 Feb 2016 15:23:04 +0000

On 12/02/16 12:32, Laurent Pinchart wrote:
> On Friday 12 February 2016 12:08:58 Will Deacon wrote:
>> On Thu, Feb 11, 2016 at 04:13:45PM +0000, Robin Murphy wrote:
>>> As the number of io-pgtable implementations grows beyond 1, it's time
>>> to rationalise the quirks mechanism before things have a chance to
>>> start getting really ugly and out-of-hand.
>>>
>>> To that end:
>>> - Indicate exactly which quirks each format can/does support.
>>> - Fail creating a table if a caller wants unsupported quirks.
>>> - Properly document where each quirk applies and why.
>>>
>>> Signed-off-by: Robin Murphy <[email-masked]>
>>> ---
>>>
>>>   drivers/iommu/io-pgtable-arm-v7s.c |  3 +++
>>>   drivers/iommu/io-pgtable-arm.c     |  2 ++
>>>   drivers/iommu/io-pgtable.c         |  3 +++
>>>   drivers/iommu/io-pgtable.h         | 24 ++++++++++++++++++++----
>>>   4 files changed, 28 insertions(+), 4 deletions(-)
>>
>> Note that I can't merge this until we've figured out the plan for Yong's
>> driver.

Indeed (hence 4/3) - it just ended up seeming like a significant enough 
change to warrant its own patch, but not critical enough to warrant 
splitting it for the sake of applying the parts touching the existing 
code right now.

>>> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c
>>> b/drivers/iommu/io-pgtable-arm-v7s.c index d39a021..9bc607a 100644
>>> --- a/drivers/iommu/io-pgtable-arm-v7s.c
>>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
>>>
>>> @@ -690,6 +690,9 @@ out_free_data:
>>>   struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns = {
>>>
>>>   	.alloc	= arm_v7s_alloc_pgtable,
>>>   	.free	= arm_v7s_free_pgtable,
>>>
>>> +	.supported_quirks = IO_PGTABLE_QUIRK_ARM_NS |
>>> +			    IO_PGTABLE_QUIRK_NO_PERMS |
>>> +			    IO_PGTABLE_QUIRK_TLBI_ON_MAP,
>>>
>>>   };
>>>
>>>   #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>>>
>>> diff --git a/drivers/iommu/io-pgtable-arm.c
>>> b/drivers/iommu/io-pgtable-arm.c index 4095af2..32f94f1 100644
>>> --- a/drivers/iommu/io-pgtable-arm.c
>>> +++ b/drivers/iommu/io-pgtable-arm.c
>>> @@ -863,6 +863,7 @@ arm_32_lpae_alloc_pgtable_s2(struct io_pgtable_cfg
>>> *cfg, void *cookie)>
>>>   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,
>>>
>>> +	.supported_quirks = IO_PGTABLE_QUIRK_ARM_NS,
>>>
>>>   };
>>>
>>>   struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
>>>
>>> @@ -873,6 +874,7 @@ struct io_pgtable_init_fns
>>> io_pgtable_arm_64_lpae_s2_init_fns = {>
>>>   struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s1_init_fns = {
>>>
>>>   	.alloc	= arm_32_lpae_alloc_pgtable_s1,
>>>   	.free	= arm_lpae_free_pgtable,
>>>
>>> +	.supported_quirks = IO_PGTABLE_QUIRK_ARM_NS,
>>>
>>>   };
>>>
>>>   struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
>>>
>>> diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
>>> index 876f6a7..0f57a45 100644
>>> --- a/drivers/iommu/io-pgtable.c
>>> +++ b/drivers/iommu/io-pgtable.c
>>> @@ -52,6 +52,9 @@ struct io_pgtable_ops *alloc_io_pgtable_ops(enum
>>> io_pgtable_fmt fmt,>
>>>   	if (!fns)
>>>   	
>>>   		return NULL;
>>>
>>> +	if (cfg->quirks & ~fns->supported_quirks)
>>> +		return NULL;
>>> +
>>>
>>>   	iop = fns->alloc(cfg, cookie);
>>>   	if (!iop)
>>>   	
>>>   		return NULL;
>>>
>>> diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
>>> index 4faee7d..6e7f11e 100644
>>> --- a/drivers/iommu/io-pgtable.h
>>> +++ b/drivers/iommu/io-pgtable.h
>>> @@ -47,10 +47,24 @@ struct iommu_gather_ops {
>>>
>>>    *                 page table walker.
>>>    */
>>>
>>>   struct io_pgtable_cfg {
>>>
>>> -	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0) /* Set NS bit in PTEs */
>>> -	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1) /* No AP/XN bits */
>>> -	#define IO_PGTABLE_QUIRK_TLBI_ON_MAP	BIT(2) /* TLB Inv. on map */
>>> -	int				quirks;
>>> +	/*
>>> +	 * IO_PGTABLE_QUIRK_ARM_NS: (ARM formats) Set NS and NSTABLE bits in
>>> +	 *	stage 1 PTEs, for hardware which insists on validating them
>>> +	 *	even in	non-secure state where they should normally be ignored.
>>> +	 *
>>> +	 * IO_PGTABLE_QUIRK_NO_PERMS: Ignore the IOMMU_READ, IOMMU_WRITE and
>>> +	 *	IOMMU_NOEXEC flags and map everything with full access, for
>>> +	 *	hardware which does not implement the permissions of a given
>>> +	 *	format, and/or requires some format-specific default value.
>>> +	 *
>>> +	 * IO_PGTABLE_QUIRK_TLBI_ON_MAP: If the format forbids caching
> invalid
>>> +	 *	(unmapped) entries but the hardware might do so anyway, perform
>>> +	 *	TLB maintenance when mapping as well as when unmapping.
>>> +	 */
>>
>> Much better, cheers.
>>
>>> +	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
>>> +	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
>>> +	#define IO_PGTABLE_QUIRK_TLBI_ON_MAP	BIT(2)
>>> +	unsigned int			quirks;
>>
>> Let's just make this unsigned long.
>>
>>>   	unsigned long			pgsize_bitmap;
>>>   	unsigned int			ias;
>>>   	unsigned int			oas;
>>>
>>> @@ -173,10 +187,12 @@ static inline void io_pgtable_tlb_sync(struct
>>> io_pgtable *iop)
>>>    *
>>>    * @alloc: Allocate a set of page tables described by cfg.
>>>    * @free:  Free the page tables associated with iop.
>>> + * @supported_quirks: Bitmap of quirks supported by the format.
>>>    */
>>>   struct io_pgtable_init_fns {
>>>   	struct io_pgtable *(*alloc)(struct io_pgtable_cfg *cfg, void
> *cookie);
>>>   	void (*free)(struct io_pgtable *iop);
>>> +	unsigned int supported_quirks;
>>>   };
>>
>> My only gripe here is that this is supposed to be a struct of function
>> pointers... get_supported_quirks() ?
>
> Can't we instead say it's a struct of function pointers and static data ? :-)
> A function to retrieve the supported quirks will just contribute to kernel
> bloat without adding any extra benefit.

Bleh - personally I think it's marginally more obvious and readable to 
have the information looking like data, but I'd much sooner just have a 
hard-coded "if (cfq->quirks & ..." check in every format's alloc 
function than introduce a whole new callback. Does that sound like a 
reasonable compromise?

Robin.