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

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Message-ID: <CABQgh9EWysbiOJv1HwpB-EUzxDbOcumnXzAn-p2PvsyB4ZcQJg@mail.gmail.com>
Date: Mon, 8 Sep 2025 14:33:25 +0800
From: Zhangfei Gao <zhangfei.gao@...aro.org>
To: Greg KH <gregkh@...uxfoundation.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

Hi Greg

On Sat, 6 Sept 2025 at 20:03, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> 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

OK，it's fine.

> call?  I don't know, what do other drivers do?

Found one example in kernel/events/uprobes.c

commit c16e2fdd746c78f5b2ce3c2ab8a26a61b6ed09e5
Author: Oleg Nesterov <oleg@...hat.com>
Date:   Sun Sep 29 16:42:58 2024 +0200

    uprobes: deny mremap(xol_vma)

+static int xol_mremap(const struct vm_special_mapping *sm, struct
vm_area_struct *new_vma)
+{
+       return -EPERM;
+}


Thanks