linux-kernel - Re: [PATCH V2 2/2] include: linux: Update gather only if it's not NULL

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Message-ID: <deda486f-8d1c-4990-9636-d267831247bd@nvidia.com>
Date: Mon, 5 Aug 2024 09:55:01 +0530
From: Ashish Mhetre <amhetre@...dia.com>
To: Robin Murphy <robin.murphy@....com>, will@...nel.org, joro@...tes.org
Cc: linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH V2 2/2] include: linux: Update gather only if it's not
 NULL


On 8/1/2024 10:12 PM, Robin Murphy wrote:
> External email: Use caution opening links or attachments
>
>
> On 01/08/2024 4:34 am, Ashish Mhetre wrote:
>> Gather can be NULL when unmap is called for freeing old table while
>> mapping. If it's NULL then there is no need to add page for syncing
>> the TLB.
>
> But that's only because __arm_lpae_unmap() is now choosing to
> over-invalidate the table entries for simplicity. I think it would make
> more sense to handle that at the callsite, e.g. "if (gather &&
> !iommu_iotlb_gather_queued(gather))".
>
> Also doesn't this mean that bisection is broken as-is since patch #1 on
> its own is going to blow up dereferencing NULL->pgsize when it gets here?
>
> Thanks,
> Robin.
>
Yes, gather can be NULL because of patch #1 only. I will fix it at 
callsite only
with a single patch rather than splitting.

>> Signed-off-by: Ashish Mhetre <amhetre@...dia.com>
>> ---
>>   include/linux/iommu.h | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 4d47f2c33311..2a28c1ef8517 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -928,6 +928,9 @@ static inline void 
>> iommu_iotlb_gather_add_page(struct iommu_domain *domain,
>>                                              struct 
>> iommu_iotlb_gather *gather,
>>                                              unsigned long iova, 
>> size_t size)
>>   {
>> +     if (!gather)
>> +             return;
>> +
>>       /*
>>        * If the new page is disjoint from the current range or is 
>> mapped at
>>        * a different granularity, then sync the TLB so that the gather