linux-kernel - Re: [PATCH RFC] mm: Add f

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Message-ID: <YiQv7JEBPzgYUTTa@casper.infradead.org>
Date:   Sun, 6 Mar 2022 03:52:12 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Nathaniel McCallum <nathaniel@...fian.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        linux-sgx@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, codalist@...a.cs.cmu.edu,
        linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH RFC] mm: Add f_ops->populate()

On Sun, Mar 06, 2022 at 05:21:11AM +0200, Jarkko Sakkinen wrote:
> On Sun, Mar 06, 2022 at 02:57:55AM +0000, Matthew Wilcox wrote:
> > On Sun, Mar 06, 2022 at 04:15:33AM +0200, Jarkko Sakkinen wrote:
> > > Sometimes you might want to use MAP_POPULATE to ask a device driver to
> > > initialize the device memory in some specific manner. SGX driver can use
> > > this to request more memory by issuing ENCLS[EAUG] x86 opcode for each
> > > page in the address range.
> > > 
> > > Add f_ops->populate() with the same parameters as f_ops->mmap() and make
> > > it conditionally called inside call_mmap(). Update call sites
> > > accodingly.
> > 
> > Your device driver has a ->mmap operation.  Why does it need another
> > one?  More explanation required here.
> 
> f_ops->mmap() would require an additional parameter, which results
> heavy refactoring.
> 
> struct file_operations has 1125 references in the kernel tree, so I
> decided to check this way around first. 

Are you saying that your device driver behaves differently if
MAP_POPULATE is set versus if it isn't?  That seems hideously broken.