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 13:21:34 +0000
From:   Song Liu <songliubraving@...com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 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)". 

Thanks,
Song

> 
> perhaps?
> 
>> 			continue;
>> 		}
>> 
>> 		pmd = pmd_offset(pud, addr);
>> 		if (pmd_none(*pmd)) {
>> +			addr &= PMD_MASK;
>> 			addr += PMD_SIZE;
>> 			continue;
>> 		}
>>