Re: [PATCH] MIPS: KDUMP: Fix to access non-sectioned memory

[David Daney <ddaney.cavm@gmail.com>]

On 10/03/2013 11:29 AM, Ralf Baechle wrote:
> On Thu, Oct 03, 2013 at 01:16:55PM +0530, Prem Mallappa wrote:
>
>> @@ -41,19 +42,20 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
>>   	if (!csize)
>>   		return 0;
>>
>> -	vaddr = kmap_atomic_pfn(pfn);
>> +	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
>
> This is not portable, I'm afraid.

It raised a red flag for me too.

I wonder, how does /dev/mem handle it?  We should probably do what the 
mem driver does for this.

David Daney


>
> Ioremap on MIPS is creating uncached mappings - on most systems, that is.
> However there is no guarantee that the data accessed through this mapping
> does not reside in a cache on another CPU or another virtual address
> which would make the operation undefined.
>
> On SGI IP27 and IP35 ioremap is not even able to create RAM mappings at
> all.  If you're lucky this would result in a bus error; if you're unlucky
> it'll make the SCSI controller scribble the answer to the universe, life
> and everything on the disk drive only to corrupt it again before you have
> a chance to read it ;-)
>
> I think this is bulletproof on Octeon so until there's a better patch you
> may want to keep this around for the SDK.
>
> I wonder, does commit 5395d97b675986e7e8f3140f9e0819d20b1d22cd
> in upstream-sfr.git fix your issue?
>
> Cheers,
>
>    Ralf
>
>
>