linux-kernel - Re: [PATCH 1/2] iommu/vt-d: Remove the dead code in init_iommu

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Date:   Thu, 1 Jun 2023 15:49:41 +0800
From:   Yanfei Xu <yanfei.xu@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>, <dwmw2@...radead.org>,
        <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>
CC:     <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] iommu/vt-d: Remove the dead code in init_iommu_hw()


On 6/1/2023 9:15 AM, Baolu Lu wrote:
> On 5/31/23 2:55 PM, Yanfei Xu wrote:
>>
>> On 5/31/2023 11:24 AM, Baolu Lu wrote:
>>> On 5/30/23 5:25 PM, Yanfei Xu wrote:
>>>> After 'commit 2a41ccee2fdc ("iommu/vt-d: Change
>>>> iommu_enable/disable_translation to return void")', init_iommu_hw() 
>>>> only
>>>> returns 0. If statement for return value of this function is 
>>>> meaningless.
>>>> Hence change init_iommu_hw() to return viod and remove the dead 
>>>> code of
>>>> if statement in init_iommu_hw()
>>>>
>>>> Signed-off-by: Yanfei Xu<yanfei.xu@...el.com>
>>>> ---
>>>>   drivers/iommu/intel/iommu.c | 12 ++----------
>>>>   1 file changed, 2 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>>>> index 8096273b034c..e98f1b122b49 100644
>>>> --- a/drivers/iommu/intel/iommu.c
>>>> +++ b/drivers/iommu/intel/iommu.c
>>>> @@ -2963,7 +2963,7 @@ static void __init 
>>>> init_no_remapping_devices(void)
>>>>   }
>>>>     #ifdef CONFIG_SUSPEND
>>>> -static int init_iommu_hw(void)
>>>> +static void init_iommu_hw(void)
>>>>   {
>>>>       struct dmar_drhd_unit *drhd;
>>>>       struct intel_iommu *iommu = NULL;
>>>> @@ -2988,8 +2988,6 @@ static int init_iommu_hw(void)
>>>>           iommu_enable_translation(iommu);
>>>>           iommu_disable_protect_mem_regions(iommu);
>>>>       }
>>>> -
>>>> -    return 0;
>>>
>>> 2966 static int init_iommu_hw(void)
>>> 2967 {
>>> 2968         struct dmar_drhd_unit *drhd;
>>> 2969         struct intel_iommu *iommu = NULL;
>>> 2970
>>> 2971         for_each_active_iommu(iommu, drhd)
>>> 2972                 if (iommu->qi)
>>> 2973                         dmar_reenable_qi(iommu);
>>>
>>> dmar_reenable_qi() still possibly returns an error number. It's better
>>> to pass this error number to the caller of init_iommu_hw()?
>>>
>> Event dmar_reenable_qi can return error number, but there is no caller
>> check it. As below, only these two places invoke it:
>> 1. init_iommu_hw->dmar_reenable_qi
>> 2. reenable_irq_remapping->dmar_reenable_qi
>>
>> I think we can also convert dmar_reenable_qi() to return void:
>> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
>> index a3414afe11b0..1432483c79e8 100644
>> --- a/drivers/iommu/intel/dmar.c
>> +++ b/drivers/iommu/intel/dmar.c
>> @@ -2112,13 +2112,10 @@ int __init enable_drhd_fault_handling(void)
>>   /*
>>    * Re-enable Queued Invalidation interface.
>>    */
>> -int dmar_reenable_qi(struct intel_iommu *iommu)
>> +void dmar_reenable_qi(struct intel_iommu *iommu)
>>   {
>> -       if (!ecap_qis(iommu->ecap))
>> -               return -ENOENT;
>> -
>> -       if (!iommu->qi)
>> -               return -ENOENT;
>> +       WARN_ON(!iommu->qi || !ecap_qis(iommu->ecap))
>> +               return;
>>
>>          /*
>>           * First disable queued invalidation.
>> @@ -2130,8 +2127,6 @@ int dmar_reenable_qi(struct intel_iommu *iommu)
>>           * invalidation.
>>           */
>>          __dmar_enable_qi(iommu);
>> -
>> -       return 0;
>>   }
>>
>>  From my understanding, dmar_reenable_qi() is used in suspend/resume 
>> case,
>> so the extended cap of an existing IOMMU hardware is unlikely 
>> changed. As
>> for the check of iommu->qi, if dmar_reenable_qi() can be invoked all is
>> depended on the no-NULL of iommu->qi at first. How about using 
>> WARN_ON for
>> both of them to simply this function.
>
> This seems to be heading in the opposite direction. Actually any
> operation may succeed or fail.
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index b871a6afd803..ecc2007a96f9 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2967,10 +2967,13 @@ static int init_iommu_hw(void)
>  {
>         struct dmar_drhd_unit *drhd;
>         struct intel_iommu *iommu = NULL;
> +       int ret;
>
> -       for_each_active_iommu(iommu, drhd)
> -               if (iommu->qi)
> -                       dmar_reenable_qi(iommu);
> +       for_each_active_iommu(iommu, drhd) {
> +               ret = dmar_reenable_qi(iommu);
> +               if (ret)
> +                       return ret;

For confirm, you mean this?
@@ -2967,10 +2970,14 @@ static int init_iommu_hw(void)
  {
         struct dmar_drhd_unit *drhd;
         struct intel_iommu *iommu = NULL;
+       int ret;

-       for_each_active_iommu(iommu, drhd)
+       for_each_active_iommu(iommu, drhd) {
                 if (iommu->qi)
-                       dmar_reenable_qi(iommu);
+                       ret = dmar_reenable_qi(iommu);
+               if (ret)
+                       return ret;
+       }

If drop NULL value check of iommu->qi, dmar_reenable_qi() may
return minus value to break the loop of dmar_reenable_qi as
one of iommus doesn't set up iommu->qi.

Thanks,
Yanfei

> + }
>
>         for_each_iommu(iommu, drhd) {
>                 if (drhd->ignored) {
>
> Best regards,
> baolu