[RFC PATCH 0/3] iommu: Permit modular builds of io-pgtable drivers

[RFC PATCH 0/3] iommu: Permit modular builds of io-pgtable drivers

[Isaac J. Manjarres]

The goal of the Generic Kernel Image (GKI) effort is to have a common
image that works across multiple Android devices. This involves generating
a kernel image that has core features integrated into it, while SoC specific
functionality can be added to the kernel for the device as a module.

Along with modularizing IOMMU drivers, this also means building the io-pgtable
code as modules, which allows for SoC vendors to only include the io-pgtable
implementations that they use. For example, GKI for arm64 must include
support for both the IOMMU ARM LPAE/V7S formats at the moment. Having the code
for both formats as modules allows SoC vendors to only provide the page table
format that they use, along with their IOMMU driver.

Modularizing both io-pgtable.c, as well as the io-pgtable-arm[-v7s].c files,
works out rather nicely, as the main interface that clients use to interact
with the page tables is already exported (i.e. alloc_io_pgtable_ops and
free_io_pgtable_ops). It also makes it so that neither the io-pgtable-arm[-v7s]
modules or the io-pgtable modules can be unloaded without unloading the IOMMU
driver, which can only happen when there aren't any references to the IOMMU
driver module.

Thanks in advance for the feedback,

Isaac J. Manjarres

Isaac J. Manjarres (3):
  iommu/io-pgtable-arm: Prepare for modularization
  iommu/io-pgtable: Prepare for modularization
  iommu/io-pgtable: Allow building as a module

 drivers/iommu/Kconfig              | 6 +++---
 drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
 drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
 drivers/iommu/io-pgtable.c         | 7 +++++--
 4 files changed, 20 insertions(+), 5 deletions(-)

-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH 1/3] iommu/io-pgtable-arm: Prepare for modularization

[Isaac J. Manjarres]

The io-pgtable-arm and io-pgtable-arm-v7s source files will
be compiled as separate modules, along with the io-pgtable
source. Export the symbols for the io-pgtable init function
structures for the io-pgtable module to use.

Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
---
 drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
 drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
index 1d92ac9..f062c1c 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -28,6 +28,7 @@
 #include <linux/iommu.h>
 #include <linux/kernel.h>
 #include <linux/kmemleak.h>
+#include <linux/module.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
@@ -839,6 +840,7 @@ struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns = {
 	.alloc	= arm_v7s_alloc_pgtable,
 	.free	= arm_v7s_free_pgtable,
 };
+EXPORT_SYMBOL_GPL(io_pgtable_arm_v7s_init_fns);
 
 #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
 
@@ -984,3 +986,5 @@ static int __init arm_v7s_do_selftests(void)
 }
 subsys_initcall(arm_v7s_do_selftests);
 #endif
+
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 87def58..2623d57 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -13,6 +13,7 @@
 #include <linux/bitops.h>
 #include <linux/io-pgtable.h>
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/sizes.h>
 #include <linux/slab.h>
 #include <linux/types.h>
@@ -1047,26 +1048,31 @@ 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,
 };
+EXPORT_SYMBOL_GPL(io_pgtable_arm_64_lpae_s1_init_fns);
 
 struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
 	.alloc	= arm_64_lpae_alloc_pgtable_s2,
 	.free	= arm_lpae_free_pgtable,
 };
+EXPORT_SYMBOL_GPL(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,
 };
+EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s1_init_fns);
 
 struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
 	.alloc	= arm_32_lpae_alloc_pgtable_s2,
 	.free	= arm_lpae_free_pgtable,
 };
+EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s2_init_fns);
 
 struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
 	.alloc	= arm_mali_lpae_alloc_pgtable,
 	.free	= arm_lpae_free_pgtable,
 };
+EXPORT_SYMBOL_GPL(io_pgtable_arm_mali_lpae_init_fns);
 
 #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
 
@@ -1252,3 +1258,5 @@ static int __init arm_lpae_do_selftests(void)
 }
 subsys_initcall(arm_lpae_do_selftests);
 #endif
+
+MODULE_LICENSE("GPL v2");
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH 1/3] iommu/io-pgtable-arm: Prepare for modularization

[Robin Murphy]

On 2020-12-18 08:38, Isaac J. Manjarres wrote:
> The io-pgtable-arm and io-pgtable-arm-v7s source files will
> be compiled as separate modules, along with the io-pgtable
> source. Export the symbols for the io-pgtable init function
> structures for the io-pgtable module to use.

In my current build tree, the io-pgtable glue itself is a whopping 379 
bytes of code and data - is there really any benefit to all the 
additional overhead of making that modular? Given the number of 
different users (including AMD now), I think at this point we should 
start considering this as part of the IOMMU core, and just tweak the 
interface such that formats can register their own init_fns dynamically 
instead of the static array that's always horrible.

Robin.

> Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
> ---
>   drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
>   drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
>   2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
> index 1d92ac9..f062c1c 100644
> --- a/drivers/iommu/io-pgtable-arm-v7s.c
> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
> @@ -28,6 +28,7 @@
>   #include <linux/iommu.h>
>   #include <linux/kernel.h>
>   #include <linux/kmemleak.h>
> +#include <linux/module.h>
>   #include <linux/sizes.h>
>   #include <linux/slab.h>
>   #include <linux/spinlock.h>
> @@ -839,6 +840,7 @@ struct io_pgtable_init_fns io_pgtable_arm_v7s_init_fns = {
>   	.alloc	= arm_v7s_alloc_pgtable,
>   	.free	= arm_v7s_free_pgtable,
>   };
> +EXPORT_SYMBOL_GPL(io_pgtable_arm_v7s_init_fns);
>   
>   #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>   
> @@ -984,3 +986,5 @@ static int __init arm_v7s_do_selftests(void)
>   }
>   subsys_initcall(arm_v7s_do_selftests);
>   #endif
> +
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 87def58..2623d57 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -13,6 +13,7 @@
>   #include <linux/bitops.h>
>   #include <linux/io-pgtable.h>
>   #include <linux/kernel.h>
> +#include <linux/module.h>
>   #include <linux/sizes.h>
>   #include <linux/slab.h>
>   #include <linux/types.h>
> @@ -1047,26 +1048,31 @@ 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,
>   };
> +EXPORT_SYMBOL_GPL(io_pgtable_arm_64_lpae_s1_init_fns);
>   
>   struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
>   	.alloc	= arm_64_lpae_alloc_pgtable_s2,
>   	.free	= arm_lpae_free_pgtable,
>   };
> +EXPORT_SYMBOL_GPL(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,
>   };
> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s1_init_fns);
>   
>   struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
>   	.alloc	= arm_32_lpae_alloc_pgtable_s2,
>   	.free	= arm_lpae_free_pgtable,
>   };
> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s2_init_fns);
>   
>   struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
>   	.alloc	= arm_mali_lpae_alloc_pgtable,
>   	.free	= arm_lpae_free_pgtable,
>   };
> +EXPORT_SYMBOL_GPL(io_pgtable_arm_mali_lpae_init_fns);
>   
>   #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>   
> @@ -1252,3 +1258,5 @@ static int __init arm_lpae_do_selftests(void)
>   }
>   subsys_initcall(arm_lpae_do_selftests);
>   #endif
> +
> +MODULE_LICENSE("GPL v2");
> 

Re: [PATCH 1/3] iommu/io-pgtable-arm: Prepare for modularization

[isaacm]

On 2020-12-18 04:38, Robin Murphy wrote:
> On 2020-12-18 08:38, Isaac J. Manjarres wrote:
>> The io-pgtable-arm and io-pgtable-arm-v7s source files will
>> be compiled as separate modules, along with the io-pgtable
>> source. Export the symbols for the io-pgtable init function
>> structures for the io-pgtable module to use.
> 
> In my current build tree, the io-pgtable glue itself is a whopping 379
> bytes of code and data - is there really any benefit to all the
> additional overhead of making that modular? Given the number of
> different users (including AMD now), I think at this point we should
> start considering this as part of the IOMMU core, and just tweak the
> interface such that formats can register their own init_fns
> dynamically instead of the static array that's always horrible.
> 
> Robin.
> 
Thanks for the feedback, Robin. This is an avenue I had explored a bit 
when modularizing the code. However,
I came up with a few problems that I couldn't get around.

1) If we leave the io-pgtable glue as part of the core kernel, we need 
to ensure that the io-pgtable format
modules get loaded prior to any driver that might use them (e.g. IOMMU 
drivers/other callers of alloc_io_pgtable_ops).
     a) This can get a bit messy, as there's no symbol dependencies 
between the callers of the io-pgtable
        code, and the page table format modules, since everything is 
through function pointers. This is handled
        for the IOMMU drivers through the devlink feature, but I don't 
see how we can leverage something like that
        here. I guess this isn't too much of a problem when everything is 
built-in, as the registration can happen
        in one of the earlier initcall levels.

     b) If we do run into a scenario where a client of io-pgtable tries 
to allocate a page table instance prior
        to the io-pgtable format module being loaded, I couldn't come up 
with a way of distinguishing between
        format module is not available at the moment vs  format module 
will never be available. I don't think
        returning EPROBE_DEFER would be something nice to do in that 
case.

2) We would have to ensure that the format module cannot be unloaded 
while other clients are using it. I suppose
this isn't as big as point #1 though, since it's something that can 
probably be handled through a similar ref count
mechanism that we're using for modular IOMMU drivers.

Given the two reasons above, I went with the current approach, since it 
avoids both issues by creating symbol dependencies
between client drivers, the io-pgtable drivers, and the io-pgtable 
format drivers, so that ensures that they are loaded
in the correct order, and also prevents them from being removed, unless 
there aren't any users present.

Thanks,
Isaac
>> Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
>> ---
>>   drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
>>   drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
>>   2 files changed, 12 insertions(+)
>> 
>> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c 
>> b/drivers/iommu/io-pgtable-arm-v7s.c
>> index 1d92ac9..f062c1c 100644
>> --- a/drivers/iommu/io-pgtable-arm-v7s.c
>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
>> @@ -28,6 +28,7 @@
>>   #include <linux/iommu.h>
>>   #include <linux/kernel.h>
>>   #include <linux/kmemleak.h>
>> +#include <linux/module.h>
>>   #include <linux/sizes.h>
>>   #include <linux/slab.h>
>>   #include <linux/spinlock.h>
>> @@ -839,6 +840,7 @@ struct io_pgtable_init_fns 
>> io_pgtable_arm_v7s_init_fns = {
>>   	.alloc	= arm_v7s_alloc_pgtable,
>>   	.free	= arm_v7s_free_pgtable,
>>   };
>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_v7s_init_fns);
>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>>   @@ -984,3 +986,5 @@ static int __init arm_v7s_do_selftests(void)
>>   }
>>   subsys_initcall(arm_v7s_do_selftests);
>>   #endif
>> +
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>> b/drivers/iommu/io-pgtable-arm.c
>> index 87def58..2623d57 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -13,6 +13,7 @@
>>   #include <linux/bitops.h>
>>   #include <linux/io-pgtable.h>
>>   #include <linux/kernel.h>
>> +#include <linux/module.h>
>>   #include <linux/sizes.h>
>>   #include <linux/slab.h>
>>   #include <linux/types.h>
>> @@ -1047,26 +1048,31 @@ 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,
>>   };
>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_64_lpae_s1_init_fns);
>>     struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
>>   	.alloc	= arm_64_lpae_alloc_pgtable_s2,
>>   	.free	= arm_lpae_free_pgtable,
>>   };
>> +EXPORT_SYMBOL_GPL(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,
>>   };
>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s1_init_fns);
>>     struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
>>   	.alloc	= arm_32_lpae_alloc_pgtable_s2,
>>   	.free	= arm_lpae_free_pgtable,
>>   };
>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s2_init_fns);
>>     struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
>>   	.alloc	= arm_mali_lpae_alloc_pgtable,
>>   	.free	= arm_lpae_free_pgtable,
>>   };
>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_mali_lpae_init_fns);
>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>>   @@ -1252,3 +1258,5 @@ static int __init arm_lpae_do_selftests(void)
>>   }
>>   subsys_initcall(arm_lpae_do_selftests);
>>   #endif
>> +
>> +MODULE_LICENSE("GPL v2");
>> 

Re: [PATCH 1/3] iommu/io-pgtable-arm: Prepare for modularization

[Robin Murphy]

On 2020-12-18 18:59, isaacm@codeaurora.org wrote:
> On 2020-12-18 04:38, Robin Murphy wrote:
>> On 2020-12-18 08:38, Isaac J. Manjarres wrote:
>>> The io-pgtable-arm and io-pgtable-arm-v7s source files will
>>> be compiled as separate modules, along with the io-pgtable
>>> source. Export the symbols for the io-pgtable init function
>>> structures for the io-pgtable module to use.
>>
>> In my current build tree, the io-pgtable glue itself is a whopping 379
>> bytes of code and data - is there really any benefit to all the
>> additional overhead of making that modular? Given the number of
>> different users (including AMD now), I think at this point we should
>> start considering this as part of the IOMMU core, and just tweak the
>> interface such that formats can register their own init_fns
>> dynamically instead of the static array that's always horrible.
>>
>> Robin.
>>
> Thanks for the feedback, Robin. This is an avenue I had explored a bit 
> when modularizing the code. However,
> I came up with a few problems that I couldn't get around.
> 
> 1) If we leave the io-pgtable glue as part of the core kernel, we need 
> to ensure that the io-pgtable format
> modules get loaded prior to any driver that might use them (e.g. IOMMU 
> drivers/other callers of alloc_io_pgtable_ops).
>      a) This can get a bit messy, as there's no symbol dependencies 
> between the callers of the io-pgtable
>         code, and the page table format modules, since everything is 
> through function pointers. This is handled
>         for the IOMMU drivers through the devlink feature, but I don't 
> see how we can leverage something like that
>         here. I guess this isn't too much of a problem when everything 
> is built-in, as the registration can happen
>         in one of the earlier initcall levels.
> 
>      b) If we do run into a scenario where a client of io-pgtable tries 
> to allocate a page table instance prior
>         to the io-pgtable format module being loaded, I couldn't come up 
> with a way of distinguishing between
>         format module is not available at the moment vs  format module 
> will never be available. I don't think
>         returning EPROBE_DEFER would be something nice to do in that case.

Urgh, I see... yes, the current approach does work out as an 
unexpectedly neat way to avoid many of the pitfalls. However I'm not 
sure it actually avoids all of them - say you have a config like this:

IPMMU_VMSA=y
-> IO_PGTABLE_ARM_LPAE=y
    -> IO_PGTABLE=y
MTK_IOMMU=m
-> IO_PGTABLE_ARMV7S=m

won't that still fail to link io-pgtable.o?

> 2) We would have to ensure that the format module cannot be unloaded 
> while other clients are using it. I suppose
> this isn't as big as point #1 though, since it's something that can 
> probably be handled through a similar ref count
> mechanism that we're using for modular IOMMU drivers.

FWIW I think that would come out in the wash from resolving 1b - I'd 
assume there would have to be some sort of module_get() in there 
somewhere. I should probably go and look at how the crypto API handles 
its modular algorithms for more inspiration...

> Given the two reasons above, I went with the current approach, since it 
> avoids both issues by creating symbol dependencies
> between client drivers, the io-pgtable drivers, and the io-pgtable 
> format drivers, so that ensures that they are loaded
> in the correct order, and also prevents them from being removed, unless 
> there aren't any users present.

Having thought all that over, I'm now wondering what we really gain from 
this either way - if vendors can build and ship SoC-tailored configs, 
then they can already turn off formats they don't care about. If the aim 
is to ship a single config everywhere, then you'll still have to 
provision and load all possible formats on any system that needs any one 
of them, thanks to those "convenient" symbol dependencies. The promise 
in the cover letter doesn't seem to materialise :/

Robin.

> 
> Thanks,
> Isaac
>>> Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
>>> ---
>>>   drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
>>>   drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
>>>   2 files changed, 12 insertions(+)
>>>
>>> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c 
>>> b/drivers/iommu/io-pgtable-arm-v7s.c
>>> index 1d92ac9..f062c1c 100644
>>> --- a/drivers/iommu/io-pgtable-arm-v7s.c
>>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
>>> @@ -28,6 +28,7 @@
>>>   #include <linux/iommu.h>
>>>   #include <linux/kernel.h>
>>>   #include <linux/kmemleak.h>
>>> +#include <linux/module.h>
>>>   #include <linux/sizes.h>
>>>   #include <linux/slab.h>
>>>   #include <linux/spinlock.h>
>>> @@ -839,6 +840,7 @@ struct io_pgtable_init_fns 
>>> io_pgtable_arm_v7s_init_fns = {
>>>       .alloc    = arm_v7s_alloc_pgtable,
>>>       .free    = arm_v7s_free_pgtable,
>>>   };
>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_v7s_init_fns);
>>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>>>   @@ -984,3 +986,5 @@ static int __init arm_v7s_do_selftests(void)
>>>   }
>>>   subsys_initcall(arm_v7s_do_selftests);
>>>   #endif
>>> +
>>> +MODULE_LICENSE("GPL v2");
>>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>>> b/drivers/iommu/io-pgtable-arm.c
>>> index 87def58..2623d57 100644
>>> --- a/drivers/iommu/io-pgtable-arm.c
>>> +++ b/drivers/iommu/io-pgtable-arm.c
>>> @@ -13,6 +13,7 @@
>>>   #include <linux/bitops.h>
>>>   #include <linux/io-pgtable.h>
>>>   #include <linux/kernel.h>
>>> +#include <linux/module.h>
>>>   #include <linux/sizes.h>
>>>   #include <linux/slab.h>
>>>   #include <linux/types.h>
>>> @@ -1047,26 +1048,31 @@ 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,
>>>   };
>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_64_lpae_s1_init_fns);
>>>     struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = {
>>>       .alloc    = arm_64_lpae_alloc_pgtable_s2,
>>>       .free    = arm_lpae_free_pgtable,
>>>   };
>>> +EXPORT_SYMBOL_GPL(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,
>>>   };
>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s1_init_fns);
>>>     struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = {
>>>       .alloc    = arm_32_lpae_alloc_pgtable_s2,
>>>       .free    = arm_lpae_free_pgtable,
>>>   };
>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s2_init_fns);
>>>     struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
>>>       .alloc    = arm_mali_lpae_alloc_pgtable,
>>>       .free    = arm_lpae_free_pgtable,
>>>   };
>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_mali_lpae_init_fns);
>>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>>>   @@ -1252,3 +1258,5 @@ static int __init arm_lpae_do_selftests(void)
>>>   }
>>>   subsys_initcall(arm_lpae_do_selftests);
>>>   #endif
>>> +
>>> +MODULE_LICENSE("GPL v2");
>>>

Re: [PATCH 1/3] iommu/io-pgtable-arm: Prepare for modularization

[isaacm]

On 2020-12-21 07:22, Robin Murphy wrote:
> On 2020-12-18 18:59, isaacm@codeaurora.org wrote:
>> On 2020-12-18 04:38, Robin Murphy wrote:
>>> On 2020-12-18 08:38, Isaac J. Manjarres wrote:
>>>> The io-pgtable-arm and io-pgtable-arm-v7s source files will
>>>> be compiled as separate modules, along with the io-pgtable
>>>> source. Export the symbols for the io-pgtable init function
>>>> structures for the io-pgtable module to use.
>>> 
>>> In my current build tree, the io-pgtable glue itself is a whopping 
>>> 379
>>> bytes of code and data - is there really any benefit to all the
>>> additional overhead of making that modular? Given the number of
>>> different users (including AMD now), I think at this point we should
>>> start considering this as part of the IOMMU core, and just tweak the
>>> interface such that formats can register their own init_fns
>>> dynamically instead of the static array that's always horrible.
>>> 
>>> Robin.
>>> 
>> Thanks for the feedback, Robin. This is an avenue I had explored a bit 
>> when modularizing the code. However,
>> I came up with a few problems that I couldn't get around.
>> 
>> 1) If we leave the io-pgtable glue as part of the core kernel, we need 
>> to ensure that the io-pgtable format
>> modules get loaded prior to any driver that might use them (e.g. IOMMU 
>> drivers/other callers of alloc_io_pgtable_ops).
>>      a) This can get a bit messy, as there's no symbol dependencies 
>> between the callers of the io-pgtable
>>         code, and the page table format modules, since everything is 
>> through function pointers. This is handled
>>         for the IOMMU drivers through the devlink feature, but I don't 
>> see how we can leverage something like that
>>         here. I guess this isn't too much of a problem when everything 
>> is built-in, as the registration can happen
>>         in one of the earlier initcall levels.
>> 
>>      b) If we do run into a scenario where a client of io-pgtable 
>> tries to allocate a page table instance prior
>>         to the io-pgtable format module being loaded, I couldn't come 
>> up with a way of distinguishing between
>>         format module is not available at the moment vs  format module 
>> will never be available. I don't think
>>         returning EPROBE_DEFER would be something nice to do in that 
>> case.
> 
> Urgh, I see... yes, the current approach does work out as an
> unexpectedly neat way to avoid many of the pitfalls. However I'm not
> sure it actually avoids all of them - say you have a config like this:
> 
> IPMMU_VMSA=y
> -> IO_PGTABLE_ARM_LPAE=y
>    -> IO_PGTABLE=y
> MTK_IOMMU=m
> -> IO_PGTABLE_ARMV7S=m
> 
> won't that still fail to link io-pgtable.o?
> 
Yes, you are correct, that would be problematic.
>> 2) We would have to ensure that the format module cannot be unloaded 
>> while other clients are using it. I suppose
>> this isn't as big as point #1 though, since it's something that can 
>> probably be handled through a similar ref count
>> mechanism that we're using for modular IOMMU drivers.
> 
> FWIW I think that would come out in the wash from resolving 1b - I'd
> assume there would have to be some sort of module_get() in there
> somewhere. I should probably go and look at how the crypto API handles
> its modular algorithms for more inspiration...
So I looked through the crypto dir, and it seems like they--along with a 
few other kernel drivers--are using MODULE_SOFTDEP()
to sort out these dependencies.
> 
>> Given the two reasons above, I went with the current approach, since 
>> it avoids both issues by creating symbol dependencies
>> between client drivers, the io-pgtable drivers, and the io-pgtable 
>> format drivers, so that ensures that they are loaded
>> in the correct order, and also prevents them from being removed, 
>> unless there aren't any users present.
> 
> Having thought all that over, I'm now wondering what we really gain
> from this either way - if vendors can build and ship SoC-tailored
> configs, then they can already turn off formats they don't care about.
> If the aim is to ship a single config everywhere, then you'll still
> have to provision and load all possible formats on any system that
> needs any one of them, thanks to those "convenient" symbol
> dependencies. The promise in the cover letter doesn't seem to
> materialise :/
> 
> Robin.
> 
Given the feedback, this makes sense. I've come up with a second version 
of the patches that leaves
the io-pgtable code in the kernel, and allows the formats to be modules, 
which better achieves what
the cover-letter is trying to express :) I believe that with the second 
patch, we should be able to
get to a place where the kernel just needs to provide io-pgtable, while 
vendors can provide either
io-pgtable-arm or io-pgtable-arm-v7s or both, as needed.
Here are the patches: 
https://lore.kernel.org/linux-iommu/1608597876-32367-1-git-send-email-isaacm@codeaurora.org/T/#t

Thanks,
Isaac
>> 
>> Thanks,
>> Isaac
>>>> Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
>>>> ---
>>>>   drivers/iommu/io-pgtable-arm-v7s.c | 4 ++++
>>>>   drivers/iommu/io-pgtable-arm.c     | 8 ++++++++
>>>>   2 files changed, 12 insertions(+)
>>>> 
>>>> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c 
>>>> b/drivers/iommu/io-pgtable-arm-v7s.c
>>>> index 1d92ac9..f062c1c 100644
>>>> --- a/drivers/iommu/io-pgtable-arm-v7s.c
>>>> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
>>>> @@ -28,6 +28,7 @@
>>>>   #include <linux/iommu.h>
>>>>   #include <linux/kernel.h>
>>>>   #include <linux/kmemleak.h>
>>>> +#include <linux/module.h>
>>>>   #include <linux/sizes.h>
>>>>   #include <linux/slab.h>
>>>>   #include <linux/spinlock.h>
>>>> @@ -839,6 +840,7 @@ struct io_pgtable_init_fns 
>>>> io_pgtable_arm_v7s_init_fns = {
>>>>       .alloc    = arm_v7s_alloc_pgtable,
>>>>       .free    = arm_v7s_free_pgtable,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_v7s_init_fns);
>>>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>>>>   @@ -984,3 +986,5 @@ static int __init arm_v7s_do_selftests(void)
>>>>   }
>>>>   subsys_initcall(arm_v7s_do_selftests);
>>>>   #endif
>>>> +
>>>> +MODULE_LICENSE("GPL v2");
>>>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>>>> b/drivers/iommu/io-pgtable-arm.c
>>>> index 87def58..2623d57 100644
>>>> --- a/drivers/iommu/io-pgtable-arm.c
>>>> +++ b/drivers/iommu/io-pgtable-arm.c
>>>> @@ -13,6 +13,7 @@
>>>>   #include <linux/bitops.h>
>>>>   #include <linux/io-pgtable.h>
>>>>   #include <linux/kernel.h>
>>>> +#include <linux/module.h>
>>>>   #include <linux/sizes.h>
>>>>   #include <linux/slab.h>
>>>>   #include <linux/types.h>
>>>> @@ -1047,26 +1048,31 @@ 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,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_64_lpae_s1_init_fns);
>>>>     struct io_pgtable_init_fns io_pgtable_arm_64_lpae_s2_init_fns = 
>>>> {
>>>>       .alloc    = arm_64_lpae_alloc_pgtable_s2,
>>>>       .free    = arm_lpae_free_pgtable,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(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,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s1_init_fns);
>>>>     struct io_pgtable_init_fns io_pgtable_arm_32_lpae_s2_init_fns = 
>>>> {
>>>>       .alloc    = arm_32_lpae_alloc_pgtable_s2,
>>>>       .free    = arm_lpae_free_pgtable,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_32_lpae_s2_init_fns);
>>>>     struct io_pgtable_init_fns io_pgtable_arm_mali_lpae_init_fns = {
>>>>       .alloc    = arm_mali_lpae_alloc_pgtable,
>>>>       .free    = arm_lpae_free_pgtable,
>>>>   };
>>>> +EXPORT_SYMBOL_GPL(io_pgtable_arm_mali_lpae_init_fns);
>>>>     #ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE_SELFTEST
>>>>   @@ -1252,3 +1258,5 @@ static int __init 
>>>> arm_lpae_do_selftests(void)
>>>>   }
>>>>   subsys_initcall(arm_lpae_do_selftests);
>>>>   #endif
>>>> +
>>>> +MODULE_LICENSE("GPL v2");
>>>> 

[PATCH 2/3] iommu/io-pgtable: Prepare for modularization

[Isaac J. Manjarres]

The io-pgtable source file uses the #ifdef preprocessor macro
to construct the io_pgtable_init_table structure. However,
the #ifdef macro evaluates to true if the config it is testing
is set to y. This is not ideal when the configs that the
io-pgtable code checks for can be m, so use IS_ENABLED() instead.
Also, add the GPL v2 module license to the io-pgtable source file.

Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
---
 drivers/iommu/io-pgtable.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
index 94394c8..867ecb4 100644
--- a/drivers/iommu/io-pgtable.c
+++ b/drivers/iommu/io-pgtable.c
@@ -10,18 +10,19 @@
 #include <linux/bug.h>
 #include <linux/io-pgtable.h>
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/types.h>
 
 static const struct io_pgtable_init_fns *
 io_pgtable_init_table[IO_PGTABLE_NUM_FMTS] = {
-#ifdef CONFIG_IOMMU_IO_PGTABLE_LPAE
+#if IS_ENABLED(CONFIG_IOMMU_IO_PGTABLE_LPAE)
 	[ARM_32_LPAE_S1] = &io_pgtable_arm_32_lpae_s1_init_fns,
 	[ARM_32_LPAE_S2] = &io_pgtable_arm_32_lpae_s2_init_fns,
 	[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,
 #endif
-#ifdef CONFIG_IOMMU_IO_PGTABLE_ARMV7S
+#if IS_ENABLED(CONFIG_IOMMU_IO_PGTABLE_ARMV7S)
 	[ARM_V7S] = &io_pgtable_arm_v7s_init_fns,
 #endif
 };
@@ -68,3 +69,5 @@ void free_io_pgtable_ops(struct io_pgtable_ops *ops)
 	io_pgtable_init_table[iop->fmt]->free(iop);
 }
 EXPORT_SYMBOL_GPL(free_io_pgtable_ops);
+
+MODULE_LICENSE("GPL v2");
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH 3/3] iommu/io-pgtable: Allow building as a module

[Isaac J. Manjarres]

Now that all of the required symbols have been exported,
and the io-pgtable code can correctly refer to the
io-pgtable init functions when their source files are built
as modules, allow the io-pgtable code to be built as a module. The
expectation is that the io-pgtable core code, along with
the descriptor format (either or both ARM LPAE and ARMV7S)
can be built as modules.

Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
---
 drivers/iommu/Kconfig | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 192ef8f..d7de6db 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -27,10 +27,10 @@ menu "Generic IOMMU Pagetable Support"
 
 # Selected by the actual pagetable implementations
 config IOMMU_IO_PGTABLE
-	bool
+	tristate
 
 config IOMMU_IO_PGTABLE_LPAE
-	bool "ARMv7/v8 Long Descriptor Format"
+	tristate "ARMv7/v8 Long Descriptor Format"
 	select IOMMU_IO_PGTABLE
 	depends on ARM || ARM64 || (COMPILE_TEST && !GENERIC_ATOMIC64)
 	help
@@ -49,7 +49,7 @@ config IOMMU_IO_PGTABLE_LPAE_SELFTEST
 	  If unsure, say N here.
 
 config IOMMU_IO_PGTABLE_ARMV7S
-	bool "ARMv7/v8 Short Descriptor Format"
+	tristate "ARMv7/v8 Short Descriptor Format"
 	select IOMMU_IO_PGTABLE
 	depends on ARM || ARM64 || COMPILE_TEST
 	help
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project