From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752335AbdKZPPH (ORCPT <rfc822;w@1wt.eu>);
        Sun, 26 Nov 2017 10:15:07 -0500
Received: from mail-wm0-f67.google.com ([74.125.82.67]:34335 "EHLO
        mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751105AbdKZPPG (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sun, 26 Nov 2017 10:15:06 -0500
X-Google-Smtp-Source: AGs4zMbEyMf5Ppguzt3otWAdYxv9wp8zCyjzXklFlQlAtM2ctQyBXNgteuH5+vcI4p9KP3uwHknNSQ==
Date: Sun, 26 Nov 2017 16:15:02 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 25/43] x86/mm/kaiser: Unmap kernel from userspace page
 tables (core patch)
Message-ID: <20171126151502.zrpwrdcx6yvrirb6@gmail.com>
References: <20171124091448.7649-1-mingo@kernel.org>
 <20171124091448.7649-26-mingo@kernel.org>
 <20171124133004.7cwe5r6hoesvod3i@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171124133004.7cwe5r6hoesvod3i@hirez.programming.kicks-ass.net>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Nov 24, 2017 at 10:14:30AM +0100, Ingo Molnar wrote:
> > +static pte_t *kaiser_shadow_pagetable_walk(unsigned long address,
> > +					   unsigned long flags)
> > +{
> > +	pte_t *pte;
> > +	pmd_t *pmd;
> > +	pud_t *pud;
> > +	p4d_t *p4d;
> > +	pgd_t *pgd = kernel_to_shadow_pgdp(pgd_offset_k(address));
> > +	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
> > +
> > +	if (flags & KAISER_WALK_ATOMIC) {
> > +		gfp &= ~GFP_KERNEL;
> > +		gfp |= __GFP_HIGH | __GFP_ATOMIC;
> > +	}
> > +
> > +	if (address < PAGE_OFFSET) {
> > +		WARN_ONCE(1, "attempt to walk user address\n");
> > +		return NULL;
> > +	}
> > +
> > +	if (pgd_none(*pgd)) {
> > +		WARN_ONCE(1, "All shadow pgds should have been populated\n");
> > +		return NULL;
> > +	}
> > +	BUILD_BUG_ON(pgd_large(*pgd) != 0);
> > +
> > +	p4d = p4d_offset(pgd, address);
> > +	BUILD_BUG_ON(p4d_large(*p4d) != 0);
> > +	if (p4d_none(*p4d)) {
> > +		unsigned long new_pud_page = __get_free_page(gfp);
> > +		if (!new_pud_page)
> > +			return NULL;
> > +
> > +		spin_lock(&shadow_table_allocation_lock);
> > +		if (p4d_none(*p4d))
> > +			set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
> > +		else
> > +			free_page(new_pud_page);
> > +		spin_unlock(&shadow_table_allocation_lock);
> 
> So mm/memory.c has two patterns here.. I prefer the other one:
> 
> 		spin_lock(&shadow_table_allocation_lock);
> 		if (p4d_none(*p4d)) {
> 			set_p4d(p4d, __p4d(_KERNEL_TABLE | __pa(new_pud_page)));
> 			new_pud_page = NULL;
> 		}
> 		spin_unlock(&shadow_table_allocation_lock);
> 		if (new_pud_page)
> 			free_page(new_pud_page);
> 
> > +	}

Ok, would be nice to get this cleanup as a delta patch, because the existing 
pattern has been tested to a fair degree already.

Thanks,

	Ingo