linux-kernel - Re: [PATCH v2 09/12] iommu/vt-d: Use cache helpers in arch_invalidate_secondary

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Date: Thu, 11 Apr 2024 16:10:15 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Tina Zhang <tina.zhang@...el.com>,
 Yi Liu <yi.l.liu@...el.com>, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/12] iommu/vt-d: Use cache helpers in
 arch_invalidate_secondary_tlbs

On 2024/4/10 23:55, Jason Gunthorpe wrote:
> On Wed, Apr 10, 2024 at 10:08:41AM +0800, Lu Baolu wrote:
>>   /* Pages have been freed at this point */
>>   static void intel_arch_invalidate_secondary_tlbs(struct mmu_notifier *mn,
>>   					struct mm_struct *mm,
>>   					unsigned long start, unsigned long end)
>>   {
>>   	struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
>> +	struct dmar_domain *domain = svm->domain;
>>   
>>   	if (start == 0 && end == -1UL) {
> 
> ULONG_MAX ideally.

Done.

> 
>> -		intel_flush_svm_all(svm);
>> +		cache_tag_flush_all(domain);
>>   		return;
>>   	}
>>   
>> -	intel_flush_svm_range(svm, start,
>> -			      (end - start + PAGE_SIZE - 1) >> VTD_PAGE_SHIFT, 0);
>> +	cache_tag_flush_range(domain, start, end, 0);
> 
> Be mindful of the note from the ARM driver:
> 
>          /*
>           * The mm_types defines vm_end as the first byte after the end address,
>           * different from IOMMU subsystem using the last address of an address
>           * range. So do a simple translation here by calculating size correctly.
>           */
>          size = end - start;

I didn't find any documentation about the @end in this callback, but in
mm subsystem, it does like this,

flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false);

So, yes, the @end in arch_invalidate_secondary_tlbs callback is
different from the iommu gather.

I was not aware of this. Thanks for pointing this out.

> 
> Given that the cache_tag_flush_range's are all tied directly to the
> iommu gather API, this is probably missing a -1 though perhaps it does
> not cause a functional problem here.

I will change it like below,

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 858a64fbdaab..15dcd1b30df1 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -146,7 +146,12 @@ static void 
intel_arch_invalidate_secondary_tlbs(struct mmu_notifier *mn,
                 return;
         }

-       cache_tag_flush_range(domain, start, end, 0);
+       /*
+        * The mm_types defines vm_end as the first byte after the end 
address,
+        * different from IOMMU subsystem using the last address of an 
address
+        * range.
+        */
+       cache_tag_flush_range(domain, start, end - 1, 0);
  }

  static void intel_mm_release(struct mmu_notifier *mn, struct mm_struct 
*mm)

Best regards,
baolu