linux-kernel - Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct vm_operations

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Date:   Sun, 15 Nov 2020 17:32:08 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <dave.hansen@...el.com>,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com, bp@...en8.de,
        cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        haitao.huang@...el.com, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, npmccallum@...hat.com, puiterwijk@...hat.com,
        rientjes@...gle.com, tglx@...utronix.de, yaozhangx@...gle.com,
        mikko.ylinen@...el.com
Subject: Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct
 vm_operations_struct

On Fri, Nov 13, 2020 at 12:01:21AM +0200, Jarkko Sakkinen wrote:
> +++ b/include/linux/mm.h
> @@ -559,6 +559,13 @@ struct vm_operations_struct {
>  	void (*close)(struct vm_area_struct * area);
>  	int (*split)(struct vm_area_struct * area, unsigned long addr);
>  	int (*mremap)(struct vm_area_struct * area);
> +	/*
> +	 * Called by mprotect() to make driver-specific permission
> +	 * checks before mprotect() is finalised.   The VMA must not
> +	 * be modified.  Returns 0 if eprotect() can proceed.
> +	 */

This is the wrong place for this documentation, and it's absurdly
specific to your implementation.  It should be in
Documentation/filesystems/locking.rst.

> +	int (*mprotect)(struct vm_area_struct *vma, unsigned long start,
> +			unsigned long end, unsigned long newflags);
> +
> +		if (vma->vm_ops && vma->vm_ops->mprotect)
> +			error = vma->vm_ops->mprotect(vma, nstart, tmp, newflags);
> +		if (error)
> +			goto out;
> +
>  		error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
>  		if (error)
>  			goto out;
> +
>  		nstart = tmp;

Spurious newline added.