linux-kernel - Re: [PATCH 3/4] uacce: implement mremap in uacce_vm

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Message-ID: <2025090608-afloat-grumbling-e729@gregkh>
Date: Sat, 6 Sep 2025 14:03:48 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Zhangfei Gao <zhangfei.gao@...aro.org>
Cc: Chenghai Huang <huangchenghai2@...wei.com>, wangzhou1@...ilicon.com,
	linux-kernel@...r.kernel.org, linuxarm@...wei.com,
	linux-crypto@...r.kernel.org, fanghao11@...wei.com,
	shenyang39@...wei.com, qianweili@...wei.com,
	linwenkai6@...ilicon.com, liulongfang@...wei.com
Subject: Re: [PATCH 3/4] uacce: implement mremap in uacce_vm_ops to return
 -EPERM

On Thu, Aug 28, 2025 at 01:59:48PM +0800, Zhangfei Gao wrote:
> Hi, Greg
> 
> On Fri, 22 Aug 2025 at 19:46, Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Fri, Aug 22, 2025 at 06:39:03PM +0800, Chenghai Huang wrote:
> > > From: Yang Shen <shenyang39@...wei.com>
> > >
> > > The current uacce_vm_ops does not support the mremap operation of
> > > vm_operations_struct. Implement .mremap to return -EPERM to remind
> > > users
> >
> > Why is this needed?  If mremap is not set, what is the value returned?
> 
> Did some debug locally.
> 
> By default, mremap is permitted.
> 
> With mremap, the original vma is released,
> The vma_close is called and free resources, including q->qfr.
> 
> However, vma->vm_private_data (q) is copied to the new vma.
> When the new vma is closed, vma_close will get q and q->qft=0.
> 
> So disable mremap here looks safer.
> 
> >
> > And why is -EPERM the correct value to return here?  That's not what the
> > man pages say is valid :(
> 
> if disable mremap, -1 is returned as MAP_FAILED.
> The errno is decided by the return value, -EPERM (-1) or -EINVAL (-22).
> man mremap only lists -EINVAL.
> 
> However, here the driver wants to disable mremap, looks -EPERM is more suitable.

Disabling mremap is not a permission issue, it's more of an invalid
call?  I don't know, what do other drivers do?

thanks,

greg k-h