Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 7 Jul 2020 05:10:46 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        x86@kernel.org, linux-sgx@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jethro Beekman <jethro@fortanix.com>,
        andriy.shevchenko@linux.intel.com, asapek@google.com, bp@alien8.de,
        cedric.xing@intel.com, chenalexchen@google.com,
        conradparker@google.com, cyhanish@google.com,
        dave.hansen@intel.com, haitao.huang@intel.com,
        josh@joshtriplett.org, kai.huang@intel.com, kai.svahn@intel.com,
        kmoy@google.com, ludloff@google.com, luto@kernel.org,
        nhorman@redhat.com, npmccallum@redhat.com, puiterwijk@redhat.com,
        rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com
Subject: Re: [PATCH v34 10/24] mm: Add vm_ops->mprotect()
Message-ID: <20200707041046.GI25523@casper.infradead.org>
References: <20200707030204.126021-1-jarkko.sakkinen@linux.intel.com>
 <20200707030204.126021-11-jarkko.sakkinen@linux.intel.com>
 <20200707031424.GD25523@casper.infradead.org>
 <20200707032254.GB5208@linux.intel.com>
 <20200707032408.GE25523@casper.infradead.org>
 <20200707040151.GA143804@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200707040151.GA143804@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jul 07, 2020 at 07:01:51AM +0300, Jarkko Sakkinen wrote:
> On Tue, Jul 07, 2020 at 04:24:08AM +0100, Matthew Wilcox wrote:
> > On Mon, Jul 06, 2020 at 08:22:54PM -0700, Sean Christopherson wrote:
> > > On Tue, Jul 07, 2020 at 04:14:24AM +0100, Matthew Wilcox wrote:
> > > > > +		if (vma->vm_ops && vma->vm_ops->mprotect) {
> > > > > +			error = vma->vm_ops->mprotect(vma, nstart, tmp, prot);
> > > > > +			if (error)
> > > > > +				goto out;
> > > > > +		}
> > > 
> > > Based on "... and then the vma owner can do whatever it needs to before
> > > calling mprotect_fixup(), which is already not static", my interpretation
> > > is that Matthew's intent was to do:
> > > 
> > > 		if (vma->vm_ops && vma->vm_ops->mprotect)
> > > 			error =  = vma->vm_ops->mprotect(vma, nstart, tmp, prot);
> > > 		else
> > > 			error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
> > > 		if (error)
> > > 			goto out;
> > > 
> > > i.e. make .mprotect() a full replacement as opposed to a prereq hook.
> > 
> > Yes, it was.  I was just looking at the next patch to be sure this was
> > how I'd been misunderstood.
> 
> I'm don't get this part. If mprotect_fixup is called in the tail of the
> callback, why it has to be called inside the callback and not be called
> after the callback?

Because that's how every other VM operation works.  Look at your
implementation of get_unmapped_area() for example.