Re: data consistency of high page

["Dennis.Yxun" <dennis.yxun@gmail.com>]

Hi NamJae:
 We hit pretty much the same problem, highmem + cache consistence
but our hardware should have cache alias problem
 Could you try attached following patch?

dmesg:
[    0.000000] PID hash table entries: 1024 (order: 0, 4096 bytes)              
[    0.000000] Dentry cache hash table entries: 32768 (order: 5, 131072 bytes)  
[    0.000000] Inode-cache hash table entries: 16384 (order: 4, 65536 bytes)    
[    0.000000] Primary instruction cache 16kB, VIPT, 4-way, linesize 32 bytes.  
[    0.000000] Primary data cache 16kB, 4-way, VIPT, no aliases, linesize 32 byt
es                                                                              
[    0.000000] MIPS secondary cache 128kB, 8-way, linesize 32 bytes.            
[    0.000000] Writing ErrCtl register=00000000                                 
[    0.000000] Readback ErrCtl register=00000000                                
[    0.000000] Memory: 510548k/262144k available (2728k kernel code, 13740k rese
rved, 630k data, 5784k init, 262144k highmem) 

diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
index 00d70c8..536b7f9 100644
--- a/arch/mips/mm/cache.c
+++ b/arch/mips/mm/cache.c
@@ -15,6 +15,7 @@
 #include <linux/sched.h>
 #include <linux/syscalls.h>
 #include <linux/mm.h>
+#include <linux/highmem.h>
 
 #include <asm/cacheflush.h>
 #include <asm/processor.h>
@@ -83,8 +84,13 @@ void __flush_dcache_page(struct page *page)
        struct address_space *mapping = page_mapping(page);
        unsigned long addr;
 
-       if (PageHighMem(page))
+       if (PageHighMem(page) &&
+               (addr = (unsigned long) kmap_atomic(page, KM_SYNC_DCACHE))) {
+               flush_data_cache_page(addr);
+               kunmap_atomic((void *)addr, KM_SYNC_DCACHE);
                return;
+       }

On Tue, Apr 5, 2011 at 4:17 PM, NamJae Jeon <linkinjeon@gmail.com> wrote:

Hi.

As you know, there is cache operation about highpage in arm arch.

arch/arm/mm/flush.c
-----------------------------------------------------------------------------------------------
if (!PageHighMem(page)) {
               __cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
       } else {
               void *addr = kmap_high_get(page);
               if (addr) {
                       __cpuc_flush_dcache_area(addr, PAGE_SIZE);
                       kunmap_high(page);
               } else if (cache_is_vipt()) {
                       /* unmapped pages might still be cached */
                       addr = kmap_atomic(page);
                       __cpuc_flush_dcache_area(addr, PAGE_SIZE);
                       kunmap_atomic(addr);
               }
       }
-------------------------------------------------------------------------------------------------

currently, mips kernel just return without cache operation.

Would you plz tell me your opinion ?

Thanks.


2010/3/23 NamJae Jeon <linkinjeon@gmail.com>:

> Hi. Ralf.
>
> I'm Namjae.jeon. nice to meet you.
>
> I face cache aliasing problem on mips 34ke.
>
> Our target cache is 34kB 4way i/d-cache , 32bytes linesize.
>
> As you know, there is possibility of cache aliasing on 8kB per way.
>
> But mips arch of kernel mainline can not properly  handile this case.
>
> For example, highmem handling in __fluash_dcache_page function is just return.
>
> So, if argument page is page in highmem, it can not flush in dcache line.
>
> I want to listen your opinion.
>
> Thanks.
>
>
> 2010/3/23 Minchan Kim <minchan.kim@gmail.com>:
>> Hi, Ralf.
>>
>> Below is thread long time ago.
>> At that time, we can't end up the problem by some reason.
>> Sorry for that.
>>
>> The problem would occur, again.
>>
>> On Fri, Oct 16, 2009 at 6:24 PM, Ralf Baechle <ralf@linux-mips.org> wrote:
>>> On Fri, Oct 16, 2009 at 02:17:19PM +0900, Minchan Kim wrote:
>>>
>>>> Many code of kernel fs usually allocate high page and flush.
>>>> But flush_dcache_page of mips checks PageHighMem to avoid flush
>>>> so that data consistency is broken, I think.
>>>
>>> What processor and cache configuration?
>>>
>>>> I found it's by you and Atsushi-san on 585fa724.
>>>> Why do we need the check?
>>>> Could you elaborte please?
>>>
>>> The if statement exists because __flush_dcache_page would crash if a page
>>> is not mapped.  This of course isn't correct but that wasn't a problem
>>> since highmem still is only supported on machines that don't have aliases.
>>>
>>>  Ralf
>>>
>>
>> Our system is following as.
>>
>> mips 34ke
>> primary i-cache 32kB VIPT 4way 32 byte line size.
>> primary d-cache 32kB 4way  32 bytes linesize
>>
>> If you have further questions, Namjae, Could you follow question of Ralf?
>>
>> --
>> Kind regards,
>> Minchan Kim
>>
>