linux-kernel - Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by PUD

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Date:   Tue, 20 Aug 2019 15:39:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Song Liu <songliubraving@...com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr
 by PUD_SIZE

On Tue, 20 Aug 2019, Song Liu wrote:
> > On Aug 20, 2019, at 4:16 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > 
> > On Tue, 20 Aug 2019, Peter Zijlstra wrote:
> >> What that code wants to do is skip to the end of the pud, a pmd_size
> >> increase will not do that. And right below this, there's a second
> >> instance of this exact pattern.
> >> 
> >> Did I get the below right?
> >> 
> >> ---
> >> diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> >> index b196524759ec..32b20b3cb227 100644
> >> --- a/arch/x86/mm/pti.c
> >> +++ b/arch/x86/mm/pti.c
> >> @@ -330,12 +330,14 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
> >> 
> >> 		pud = pud_offset(p4d, addr);
> >> 		if (pud_none(*pud)) {
> >> +			addr &= PUD_MASK;
> >> 			addr += PUD_SIZE;
> > 
> > 			round_up(addr, PUD_SIZE);
> 
> I guess we need "round_up(addr + PMD_SIZE, PUD_SIZE)". 

Right you are.