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Date:   Fri, 8 Jul 2022 14:58:51 +0300
From:   Serge Semin <fancer.lancer@gmail.com>
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     linux-mips@vger.kernel.org, gerg@kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] MIPS: Fixed __debug_virt_addr_valid()
Message-ID: <20220708115851.ejsooiilxcopkoei@mobilestation>
References: <20220707215237.1730283-1-f.fainelli@gmail.com>
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On Thu, Jul 07, 2022 at 02:52:36PM -0700, Florian Fainelli wrote:
> It is permissible for kernel code to call virt_to_phys() against virtual
> addresses that are in KSEG0 or KSEG1 and we need to be dealing with both
> types. Add a final condition that ensures that the virtual address is
> below KSEG2.
> 
> Fixes: dfad83cb7193 ("MIPS: Add support for CONFIG_DEBUG_VIRTUAL")
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  arch/mips/mm/physaddr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/mm/physaddr.c b/arch/mips/mm/physaddr.c
> index a1ced5e44951..a82f8f57a652 100644
> --- a/arch/mips/mm/physaddr.c
> +++ b/arch/mips/mm/physaddr.c
> @@ -5,6 +5,7 @@
>  #include <linux/mmdebug.h>
>  #include <linux/mm.h>
>  
> +#include <asm/addrspace.h>
>  #include <asm/sections.h>
>  #include <asm/io.h>
>  #include <asm/page.h>
> @@ -30,7 +31,7 @@ static inline bool __debug_virt_addr_valid(unsigned long x)
>  	if (x == MAX_DMA_ADDRESS)
>  		return true;
>  

> -	return false;
> +	return KSEGX(x) < KSEG2;

With this do we really need the high_memory-based conditionals in this
method?

If the line above is the only way to take the uncached segment into
account then can we reduce the whole method to:
static inline bool __debug_virt_addr_valid {
	return x >= PAGE_OFFSET && KSEGX(x) < KSEG2;
}
?

Though this still may be invalid for EVA systems, like malta (see
arch/mips/include/asm/mach-malta/spaces.h).

Note AFAICS if EVA is enabled, highmem is implied to be disabled (see
the CPU_MIPS32_3_5_EVA config utilization and HIGHMEM config
dependencies). Thus all the memory is supposed to be linearly mapped
in that case.

-Sergey

>  }
>  
>  phys_addr_t __virt_to_phys(volatile const void *x)
> -- 
> 2.25.1
>