RE: [PATCH] arm64: dts: r9a07g044: Add complete CPU cache information

[Biju Das]

Hi Tim Pambor,

> -----Original Message-----
> From: Tim Pambor <tp@xxxxxxxxxxxxx>
> Sent: Wednesday, March 6, 2024 10:11 AM
> Subject: Re: [PATCH] arm64: dts: r9a07g044: Add complete CPU cache information
> 
> Hi Biju,
> 
> thanks for the review.
> 
> > Hi Tim Pambor,
> >
> > Thanks for the patch.
> >
> > > -----Original Message-----
> > > From: Tim Pambor <tp@xxxxxxxxxxxxx>
> > > Sent: Tuesday, March 5, 2024 3:14 PM
> > > Subject: [PATCH] arm64: dts: r9a07g044: Add complete CPU cache
> > > information
> > >
> > > Based on ARM Cortex-A55 TRM and RZG2/L user's manual, each Cortex-
> > > A55 has
> >
> > RZ/G2L
> >
> > > - 32 KB of L1 4-way, set-associative instruction cache
> > > - 32 KB of L1 4-way, set-associative data cache
> > >
> > > Each cache has a cache line length of 64B and therefore there are
> > > 32768B/(4 * 64B)=128 sets for each cache.
> > >
> > > RZG2/L are not configured with the optional per-core L2 cache but
> > > only have a L3 cache shared among all
> > RZ/G2L
> > > cores. In this case, the L3 cache appears as a L2 cache to the
> > > system. Therefore, specify "cache-level = <2>" for the L3 cache.
> >
> 
> I will send a v2 with the commit message corrected.
> 
> > You mean for L3 Cache, cache-level = <2> if there is no L2 Cache on
> > the system? Does it need any update on dt-bindings to make this clear?
> 
> I followed the approach chosen for the Rockchip RK356x, which also has a Cortex-A55 with an L3 cache
> but no L2 cache [1]. I can add a comment to the device tree explaining that there is no L2 cache and
> that therefore the L3 cache appears as a L2 cache to the system. Do you consider that sufficient?

I am leaving this to Geert and other DT maintainer's for their view on this topic.

Cheers,
Biju

> 
> 
> Currently, having cache-level = <3> also causes a out-of-bounds access in populate_cache_leaves.
> 
> [    0.066217] ==================================================================
> [    0.066369] BUG: KASAN: slab-out-of-bounds in populate_cache_leaves+0x25c/0x2d0
> [    0.066495] Write of size 4 at addr ffff0000082370dc by task swapper/0/1
> [    0.066580]
> [    0.066619] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.8.0-rc2-00016-g30d5a685c65d #6
> [    0.066719] Hardware name: MYC-YG2LX (DT)
> [    0.066793] Call trace:
> [    0.066836]  dump_backtrace+0x98/0x118
> [    0.066900]  show_stack+0x18/0x24
> [    0.066959]  dump_stack_lvl+0x60/0xac
> [    0.067029]  print_report+0xf8/0x5d8
> [    0.067096]  kasan_report+0xc0/0x100
> [    0.067159]  __asan_report_store4_noabort+0x20/0x2c
> [    0.067235]  populate_cache_leaves+0x25c/0x2d0
> [    0.067308]  detect_cache_attributes+0x34c/0x1998
> [    0.067384]  update_siblings_masks+0x30/0x554
> [    0.067460]  store_cpu_topology+0xe8/0x188
> [    0.067528]  smp_prepare_cpus+0x5c/0x238
> [    0.067602]  kernel_init_freeable+0x258/0xb18
> [    0.067673]  kernel_init+0x30/0x208
> [    0.067736]  ret_from_fork+0x10/0x20
> [    0.067802]
> [    0.067835] Allocated by task 1:
> [    0.067889]  kasan_save_stack+0x3c/0x64
> [    0.067956]  kasan_save_track+0x20/0x3c
> [    0.068020]  kasan_save_alloc_info+0x68/0x78
> [    0.068090]  __kasan_kmalloc+0xd4/0xd8
> [    0.068154]  __kmalloc+0x1c0/0x430
> [    0.068215]  allocate_cache_info+0xa8/0x204
> [    0.068284]  fetch_cache_info+0xc4/0x200
> [    0.068349]  init_cpu_topology+0x348/0x45c
> [    0.068423]  smp_prepare_cpus+0x1c/0x238
> [    0.068492]  kernel_init_freeable+0x258/0xb18
> [    0.068561]  kernel_init+0x30/0x208
> [    0.068622]  ret_from_fork+0x10/0x20
> [    0.068685]
> [    0.068719] The buggy address belongs to the object at ffff000008237000
> [    0.068719]  which belongs to the cache kmalloc-256 of size 256
> [    0.068849] The buggy address is located 4 bytes to the right of
> [    0.068849]  allocated 216-byte region [ffff000008237000, ffff0000082370d8)
> [    0.068984]
> [    0.069018] The buggy address belongs to the physical page:
> [    0.069089] page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
> pfn:0x48236
> [    0.069201] head:(____ptrval____) order:1 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> [    0.069297] flags: 0x840(slab|head|zone=0)
> [    0.069366] page_type: 0xffffffff()
> [    0.069430] raw: 0000000000000840 ffff000008001b40 dead000000000122 0000000000000000
> [    0.069526] raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
> [    0.069616] page dumped because: kasan: bad access detected
> [    0.069684]
> [    0.069717] Memory state around the buggy address:
> [    0.069781]  ffff000008236f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [    0.069870]  ffff000008237000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [    0.069958] >ffff000008237080: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
> [    0.070042]                                                     ^
> [    0.070116]  ffff000008237100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [    0.070204]  ffff000008237180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [    0.070290] ==================================================================
> 
> [1] https://lore.kernel.org/linux-
> rockchip/2285ee41e165813011220f9469e28697923aa6e0.1709491108.git.dsimic@xxxxxxxxxxx/
> 
> >
> > Cheers,
> > Biju
> >