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 05:39:04 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>, x86@kernel.org,
        linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jethro Beekman <jethro@fortanix.com>,
        Haitao Huang <haitao.huang@linux.intel.com>,
        Chunyang Hui <sanqian.hcy@antfin.com>,
        Jordan Hand <jorhand@linux.microsoft.com>,
        Nathaniel McCallum <npmccallum@redhat.com>,
        Seth Moore <sethmo@google.com>,
        Suresh Siddha <suresh.b.siddha@intel.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, puiterwijk@redhat.com, rientjes@google.com,
        tglx@linutronix.de, yaozhangx@google.com
Subject: Re: [PATCH v34 11/24] x86/sgx: Add SGX enclave driver
Message-ID: <20200707043904.GJ25523@casper.infradead.org>
References: <20200707030204.126021-1-jarkko.sakkinen@linux.intel.com>
 <20200707030204.126021-12-jarkko.sakkinen@linux.intel.com>
 <20200707033617.GF25523@casper.infradead.org>
 <20200707041151.GE143804@linux.intel.com>
 <20200707042904.GD5208@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200707042904.GD5208@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jul 06, 2020 at 09:29:04PM -0700, Sean Christopherson wrote:
> > > > +	idx_start = PFN_DOWN(start);
> > > > +	idx_end = PFN_DOWN(end - 1);
> > > > +
> > > > +	for (idx = idx_start; idx <= idx_end; ++idx) {
> > > > +		mutex_lock(&encl->lock);
> > > > +		page = radix_tree_lookup(&encl->page_tree, idx);
> > > > +		mutex_unlock(&encl->lock);
> > > > +
> > > > +		if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
> > > > +			return -EACCES;
> > > 
> > > You should really use an iterator here instead of repeated lookups.
> > > xas_for_each() will probably be what you want.
> > 
> > Thank you for your remarks. I'll look into using xarray for this.
> 
> Question for Matthew:
> 
> To enforce the "page must be populated" rule, is there a clean way to retrieve
> the index of the current entry?  Our entries/pages don't have information
> about their index.  Or should we just count the number of entries and check
> 'em at the end? E.g.
> 
>         xas_for_each(...) {
>                 if (~page->vm_max_prot_bits & vm_prot_bits)
>                         return -EACCES;
>                 nr_entries++;
>         }
> 
>         if (nr_entries != (end_index - start_index))
>                 return -EACCES;

Probably best just to steal the implementation from here:

pgoff_t page_cache_next_miss(struct address_space *mapping,
                             pgoff_t index, unsigned long max_scan)
{
        XA_STATE(xas, &mapping->i_pages, index);

        while (max_scan--) {
                void *entry = xas_next(&xas);
                if (!entry || xa_is_value(entry))
                        break;
                if (xas.xa_index == 0)
                        break;
        }

        return xas.xa_index;
}

although I think you have a simpler task.

	XA_STATE(xas, ..., start_index);

	for (;;) {
		struct page *page = xas_next(&xas);

		if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
			return -EACCES;
	}

	return 0;

should do the trick, I think.