linux-kernel - Re: [PATCH] mm/highmem: Take kmap_high

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Message-ID: <94783ef1-7b1c-d657-d7ee-cd6a91504efc@samsung.com>
Date:   Thu, 12 Nov 2020 12:38:50 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     vtolkm@...glemail.com, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm/highmem: Take kmap_high_get() properly into account

Hi Thomas,

On 12.11.2020 11:59, Thomas Gleixner wrote:
> kunmap_local() warns when the virtual address to unmap is below
> PAGE_OFFSET. This is correct except for the case that the mapping was
> obtained via kmap_high_get() because the PKMAP addresses are right below
> PAGE_OFFSET.
>
> Cure it by skipping the WARN_ON() when the unmap was handled by
> kunmap_high().
>
> Fixes: 298fa1ad5571 ("highmem: Provide generic variant of kmap_atomic*")
> Reported-by: vtolkm@...glemail.com
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

This fixes the issue I've reported here: 
https://lore.kernel.org/dri-devel/c07bae0c-68dd-2693-948f-00e8a50f3053@samsung.com/ 
Thanks!

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>   mm/highmem.c |   19 +++++++++++++------
>   1 file changed, 13 insertions(+), 6 deletions(-)
>
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -426,12 +426,15 @@ static inline void *arch_kmap_local_high
>   #endif
>   
>   /* Unmap a local mapping which was obtained by kmap_high_get() */
> -static inline void kmap_high_unmap_local(unsigned long vaddr)
> +static inline bool kmap_high_unmap_local(unsigned long vaddr)
>   {
>   #ifdef ARCH_NEEDS_KMAP_HIGH_GET
> -	if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP))
> +	if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {
>   		kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));
> +		return true;
> +	}
>   #endif
> +	return false;
>   }
>   
>   static inline int kmap_local_calc_idx(int idx)
> @@ -491,10 +494,14 @@ void kunmap_local_indexed(void *vaddr)
>   
>   	if (addr < __fix_to_virt(FIX_KMAP_END) ||
>   	    addr > __fix_to_virt(FIX_KMAP_BEGIN)) {
> -		WARN_ON_ONCE(addr < PAGE_OFFSET);
> -
> -		/* Handle mappings which were obtained by kmap_high_get() */
> -		kmap_high_unmap_local(addr);
> +		/*
> +		 * Handle mappings which were obtained by kmap_high_get()
> +		 * first as the virtual address of such mappings is below
> +		 * PAGE_OFFSET. Warn for all other addresses which are in
> +		 * the user space part of the virtual address space.
> +		 */
> +		if (!kmap_high_unmap_local(addr))
> +			WARN_ON_ONCE(addr < PAGE_OFFSET);
>   		return;
>   	}
>   
>
>
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland