Re: [PATCH 3/4] uacce: implement mremap in uacce_vm_ops to return -EPERM

[Greg KH <gregkh@linuxfoundation.org>]

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@linuxfoundation.org> wrote:
> >
> > On Fri, Aug 22, 2025 at 06:39:03PM +0800, Chenghai Huang wrote:
> > > From: Yang Shen <shenyang39@huawei.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