linux-kernel - Re: [PATCH] MIPS: Fixed __debug_virt_addr

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Date:   Tue, 12 Jul 2022 09:28:02 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     linux-mips@...r.kernel.org, gerg@...nel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: Fixed __debug_virt_addr_valid()

On 7/8/22 04:58, Serge Semin wrote:
> 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@...il.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.

OK, so if all of the memory is linearly mapped, then I am not too sure 
what we will be able to check, which is in essence pretty similar to 
what happens on MIPS64, right?

Maybe DEBUG_VIRTUAL should depend on !EVA as well?
-- 
Florian