linux-kernel - Re: [PATCH 2/3] x86/mm: Sync also unmappings in vmalloc_sync

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Date:   Mon, 15 Jul 2019 15:08:14 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Joerg Roedel <joro@...tes.org>
cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 2/3] x86/mm: Sync also unmappings in vmalloc_sync_one()

On Mon, 15 Jul 2019, Joerg Roedel wrote:

> From: Joerg Roedel <jroedel@...e.de>
> 
> With huge-page ioremap areas the unmappings also need to be
> synced between all page-tables. Otherwise it can cause data
> corruption when a region is unmapped and later re-used.
> 
> Make the vmalloc_sync_one() function ready to sync
> unmappings.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>

Lacks a Fixes tag methinks.

> ---
>  arch/x86/mm/fault.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 4a4049f6d458..d71e167662c3 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -194,11 +194,12 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
>  
>  	pmd = pmd_offset(pud, address);
>  	pmd_k = pmd_offset(pud_k, address);
> -	if (!pmd_present(*pmd_k))
> -		return NULL;
>  
> -	if (!pmd_present(*pmd))
> +	if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
>  		set_pmd(pmd, *pmd_k);

It took me a while to understand what this is doing. Can we please have a
comment here?

> +
> +	if (!pmd_present(*pmd_k))
> +		return NULL;

Thanks,

	tglx