linux-kernel - Re: [PATCH v10 10/10] iommu/vt-d: Add iotlb flush for nested domain

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Date: Wed, 3 Jan 2024 11:06:19 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Yi Liu <yi.l.liu@...el.com>, Jason Gunthorpe <jgg@...dia.com>
Cc: baolu.lu@...ux.intel.com, joro@...tes.org, alex.williamson@...hat.com,
 kevin.tian@...el.com, robin.murphy@....com, cohuck@...hat.com,
 eric.auger@...hat.com, nicolinc@...dia.com, kvm@...r.kernel.org,
 mjrosato@...ux.ibm.com, chao.p.peng@...ux.intel.com,
 yi.y.sun@...ux.intel.com, peterx@...hat.com, jasowang@...hat.com,
 shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
 suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 zhenzhong.duan@...el.com, joao.m.martins@...cle.com, xin.zeng@...el.com,
 yan.y.zhao@...el.com, j.granados@...sung.com
Subject: Re: [PATCH v10 10/10] iommu/vt-d: Add iotlb flush for nested domain

On 2024/1/3 9:33, Yi Liu wrote:
> On 2024/1/3 02:44, Jason Gunthorpe wrote:
>> On Tue, Jan 02, 2024 at 06:38:34AM -0800, Yi Liu wrote:
>>
>>> +static void intel_nested_flush_cache(struct dmar_domain *domain, u64 
>>> addr,
>>> +                     unsigned long npages, bool ih, u32 *error)
>>> +{
>>> +    struct iommu_domain_info *info;
>>> +    unsigned long i;
>>> +    unsigned mask;
>>> +    u32 fault;
>>> +
>>> +    xa_for_each(&domain->iommu_array, i, info)
>>> +        qi_flush_piotlb(info->iommu,
>>> +                domain_id_iommu(domain, info->iommu),
>>> +                IOMMU_NO_PASID, addr, npages, ih, NULL);
>>
>> This locking on the xarray is messed up throughout the driver. There
>> could be a concurrent detach at this point which will free info and
>> UAF this.
> 
> hmmm, xa_for_each() takes and releases rcu lock, and according to the
> domain_detach_iommu(), info is freed after xa_erase(). For an existing
> info stored in xarray, xa_erase() should return after rcu lock is released.
> is it? Any idea? @Baolu

I once thought locking for xarray is self-contained. I need more thought
on this before taking further action.

Best regards,
baolu