linux-kernel - Re: [PATCH] vfio/pci: take mmap write lock for io_remap_pfn

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Date: Wed, 22 May 2024 18:56:29 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	alex.williamson@...hat.com, kevin.tian@...el.com, jgg@...dia.com, yishaih@...dia.com, 
	shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH] vfio/pci: take mmap write lock for io_remap_pfn_range

On Mon, May 08, 2023 at 08:58:42PM GMT, Yan Zhao wrote:
> In VFIO type1, vaddr_get_pfns() will try fault in MMIO PFNs after
> pin_user_pages_remote() returns -EFAULT.
> 
> follow_fault_pfn
>  fixup_user_fault
>   handle_mm_fault
>    handle_mm_fault
>     do_fault
>      do_shared_fault
>       do_fault
>        __do_fault
>         vfio_pci_mmap_fault
>          io_remap_pfn_range
>           remap_pfn_range
>            track_pfn_remap
>             vm_flags_set         ==> mmap_assert_write_locked(vma->vm_mm)
>            remap_pfn_range_notrack
>             vm_flags_set         ==> mmap_assert_write_locked(vma->vm_mm)
> 
> As io_remap_pfn_range() will call vm_flags_set() to update vm_flags [1],
> holding of mmap write lock is required.
> So, update vfio_pci_mmap_fault() to drop mmap read lock and take mmap
> write lock.
> 
> [1] https://lkml.kernel.org/r/20230126193752.297968-3-surenb@google.com
> commit bc292ab00f6c ("mm: introduce vma->vm_flags wrapper functions")
> commit 1c71222e5f23
> ("mm: replace vma->vm_flags direct modifications with modifier calls")
>

With linux-next I started noticing traces similar to the above without
lockdep, since it has ba168b52bf8e ("mm: use rwsem assertion macros for
mmap_lock"). Were there any follow ups to this? Sorry if my quick
searching missed it.

Thanks,
drew