linux-kernel - Re: [PATCH v4 for-next 1/2] RDMA/core: Provide rdma_user_mmap_disassociate() to disassociate mmap pages

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Message-ID: <ZtxDF7EMY13tYny2@ziepe.ca>
Date: Sat, 7 Sep 2024 09:12:07 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Junxian Huang <huangjunxian6@...ilicon.com>
Cc: leon@...nel.org, linux-rdma@...r.kernel.org, linuxarm@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 for-next 1/2] RDMA/core: Provide
 rdma_user_mmap_disassociate() to disassociate mmap pages

On Thu, Sep 05, 2024 at 09:11:54PM +0800, Junxian Huang wrote:

> @@ -698,11 +700,20 @@ static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
>  	ucontext = ib_uverbs_get_ucontext_file(file);
>  	if (IS_ERR(ucontext)) {
>  		ret = PTR_ERR(ucontext);
> -		goto out;
> +		goto out_srcu;
>  	}
> +
> +	mutex_lock(&file->disassociation_lock);
> +	if (file->disassociated) {
> +		ret = -EPERM;
> +		goto out_mutex;
> +	}

What sets disassociated back to false once the driver reset is
completed?

I think you should probably drop this and instead add a lock and test
inside the driver within its mmap op. While reset is ongoing fail all
new mmaps.

>  	/*
>  	 * Disassociation already completed, the VMA should already be zapped.
>  	 */
> -	if (!ufile->ucontext)
> +	if (!ufile->ucontext || ufile->disassociated)
>  		goto out_unlock;

Is this needed? It protects agains fork, but since the driver is still
present I wonder if it is OK

> @@ -822,6 +837,8 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
>  	struct rdma_umap_priv *priv, *next_priv;
>  
>  	lockdep_assert_held(&ufile->hw_destroy_rwsem);
> +	mutex_lock(&ufile->disassociation_lock);
> +	ufile->disassociated = true;

I think this doesn't need the hw_destroy_rwsem anymore since you are
using this new disassociation_lock instead. It doesn't make alot of
sense to hold the hw_destroy_rwsem for read here, it was ment to be
held for write.

Jason