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 13:16:41 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Song Liu <songliubraving@...com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...com, 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, 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);

perhaps?

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