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Date: Fri, 6 Mar 2026 18:26:32 +0000
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Subject: Re: [PATCH 1/2] arm_mpam: Force __iomem casts
To: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>,
 Ben Horgan <ben.horgan@arm.com>, Reinette Chatre
 <reinette.chatre@intel.com>, Fenghua Yu <fenghuay@nvidia.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20260216110240.159691-3-krzysztof.kozlowski@oss.qualcomm.com>
 <7b5e4218-5961-4874-bbb1-89770cd2c744@arm.com>
 <18f3f73a-9bc6-4518-b3e4-730fa0793146@oss.qualcomm.com>
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From: James Morse <james.morse@arm.com>
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Hi Krzysztof, Ben,

On 27/02/2026 14:51, Krzysztof Kozlowski wrote:
> On 27/02/2026 15:06, Ben Horgan wrote:
>> On 2/16/26 11:02, Krzysztof Kozlowski wrote:
>>> Code allocates standard kernel memory to pass to the MPAM, which expects
>>> __iomem.  The code is safe, because __iomem accessors should work fine
>>> on kernel mapped memory, however leads to sparse warnings:
>>>
>>>   test_mpam_devices.c:327:42: warning: incorrect type in initializer (different address spaces)
>>>   test_mpam_devices.c:327:42:    expected char [noderef] __iomem *buf
>>>   test_mpam_devices.c:327:42:    got void *
>>>   test_mpam_devices.c:342:24: warning: cast removes address space '__iomem' of expression
>>>
>>> Cast the pointer to memory via __force to silence them.

>>> diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c
>>> index 3e8d564a0c64..2de41b47c138 100644
>>> --- a/drivers/resctrl/test_mpam_devices.c
>>> +++ b/drivers/resctrl/test_mpam_devices.c
>>> @@ -324,7 +324,7 @@ static void test_mpam_enable_merge_features(struct kunit *test)
>>>  
>>>  static void test_mpam_reset_msc_bitmap(struct kunit *test)
>>>  {
>>> -	char __iomem *buf = kunit_kzalloc(test, SZ_16K, GFP_KERNEL);
>>> +	char __iomem *buf = (__force char __iomem *)kunit_kzalloc(test, SZ_16K, GFP_KERNEL);
>>>  	struct mpam_msc fake_msc = {};
>>>  	u32 *test_result;
>>>  

>> This change looks good to me.

[...]

>> Acked-by: Ben Horgan <ben.horgan@arm.com>


Thanks! I've picked this for a fixes branch. I'm not sure what Will or Catalin will think
this needs fixing during the release as the driver is behind CONFIG_EXPERT. I'll ask...


Thanks,

James