linux-kernel - Re: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <e00587f2-ebfa-436b-a17a-198ff9c02f4a@linux.intel.com>
Date: Fri, 11 Jul 2025 11:09:00 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Kevin Tian <kevin.tian@...el.com>,
 Jason Gunthorpe <jgg@...dia.com>, Jann Horn <jannh@...gle.com>,
 Vasant Hegde <vasant.hegde@....com>, Dave Hansen <dave.hansen@...el.com>,
 Alistair Popple <apopple@...dia.com>, Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Andy Lutomirski <luto@...nel.org>, "Tested-by : Yi Lai" <yi1.lai@...el.com>,
 iommu@...ts.linux.dev, security@...nel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB
 flush

On 7/10/25 23:53, Peter Zijlstra wrote:
> On Thu, Jul 10, 2025 at 03:54:32PM +0200, Peter Zijlstra wrote:
> 
>>> @@ -132,8 +136,15 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>>>   	if (ret)
>>>   		goto out_free_domain;
>>>   	domain->users = 1;
>>> -	list_add(&domain->next, &mm->iommu_mm->sva_domains);
>>>   
>>> +	if (list_empty(&iommu_mm->sva_domains)) {
>>> +		scoped_guard(spinlock_irqsave, &iommu_mms_lock) {
>>> +			if (list_empty(&iommu_sva_mms))
>>> +				static_branch_enable(&iommu_sva_present);
>>> +			list_add(&iommu_mm->mm_list_elm, &iommu_sva_mms);
>>> +		}
>>> +	}
>>> +	list_add(&domain->next, &iommu_mm->sva_domains);
>>>   out:
>>>   	refcount_set(&handle->users, 1);
>>>   	mutex_unlock(&iommu_sva_lock);
>>> @@ -175,6 +186,15 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
>>>   		list_del(&domain->next);
>>>   		iommu_domain_free(domain);
>>>   	}
>>> +
>>> +	if (list_empty(&iommu_mm->sva_domains)) {
>>> +		scoped_guard(spinlock_irqsave, &iommu_mms_lock) {
>>> +			list_del(&iommu_mm->mm_list_elm);
>>> +			if (list_empty(&iommu_sva_mms))
>>> +				static_branch_disable(&iommu_sva_present);
>>> +		}
>>> +	}
>>> +
>>>   	mutex_unlock(&iommu_sva_lock);
>>>   	kfree(handle);
>>>   }
>>
>> This seems an odd coding style choice; why the extra unneeded
>> indentation? That is, what's wrong with:
>>
>> 	if (list_empty()) {
>> 		guard(spinlock_irqsave)(&iommu_mms_lock);
>> 		list_del();
>> 		if (list_empty()
>> 			static_branch_disable();
>> 	}
> 
> Well, for one, you can't do static_branch_{en,dis}able() from atomic
> context...
> 
> Was this ever tested?

I conducted unit tests for vmalloc()/vfree() scenarios, and Yi performed
fuzzing tests. We have not observed any warning messages. Perhaps
static_branch_disable() is not triggered in the test cases?

Thanks,
baolu