Re: [PATCH] powerpc: fix VMX fix for memcpy case

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

* Nishanth Aravamudan <nacc@linux.vnet.ibm.com> [2012-10-01 17:59:13]:

> [urgh, sorry Anton, Ben & Paul, inadvertently hit send before adding
> linuxppc-dev to the cc!]
> 
> Hi Anton,
> 
> In 2fae7cdb60240e2e2d9b378afbf6d9fcce8a3890 ("powerpc: Fix VMX in
> interrupt check in POWER7 copy loops"), I think you inadvertently
> introduced a regression for memcpy on POWER7 machines. copyuer and
> memcpy diverge slightly in their use of cr1 (copyuser doesn't use it,
> but memcpy does) and you end up clobbering that register with your fix.
> That results in (taken from an FC18 kernel):
> 
> [   18.824604] Unrecoverable VMX/Altivec Unavailable Exception f20 at c000000000052f40
> [   18.824618] Oops: Unrecoverable VMX/Altivec Unavailable Exception, sig: 6 [#1]
> [   18.824623] SMP NR_CPUS=1024 NUMA pSeries
> [   18.824633] Modules linked in: tg3(+) be2net(+) cxgb4(+) ipr(+) sunrpc xts lrw gf128mul dm_crypt dm_round_robin dm_multipath linear raid10 raid456 async_raid6_recov async_memcpy async_pq raid6_pq async_xor xor async_tx raid1 raid0 scsi_dh_rdac scsi_dh_hp_sw scsi_dh_emc scsi_dh_alua squashfs cramfs
> [   18.824705] NIP: c000000000052f40 LR: c00000000020b874 CTR: 0000000000000512
> [   18.824709] REGS: c000001f1fef7790 TRAP: 0f20   Not tainted  (3.6.0-0.rc6.git0.2.fc18.ppc64)
> [   18.824713] MSR: 8000000000009032 <SF,EE,ME,IR,DR,RI>  CR: 4802802e  XER: 20000010
> [   18.824726] SOFTE: 0
> [   18.824728] CFAR: 0000000000000f20
> [   18.824731] TASK = c000000fa7128400[0] 'swapper/24' THREAD: c000000fa7480000 CPU: 24
> GPR00: 00000000ffffffc0 c000001f1fef7a10 c00000000164edc0 c000000f9b9a8120
> GPR04: c000000f9b9a8124 0000000000001438 0000000000000060 03ffffff064657ee
> GPR08: 0000000080000000 0000000000000010 0000000000000020 0000000000000030
> GPR12: 0000000028028022 c00000000ff25400 0000000000000001 0000000000000000
> GPR16: 0000000000000000 7fffffffffffffff c0000000016b2180 c00000000156a500
> GPR20: c000000f968c7a90 c0000000131c31d8 c000001f1fef4000 c000000001561d00
> GPR24: 000000000000000a 0000000000000000 0000000000000001 0000000000000012
> GPR28: c000000fa5c04f80 00000000000008bc c0000000015c0a28 000000000000022e
> [   18.824792] NIP [c000000000052f40] .memcpy_power7+0x5a0/0x7c4
> [   18.824797] LR [c00000000020b874] .pcpu_free_area+0x174/0x2d0
> [   18.824800] Call Trace:
> [   18.824803] [c000001f1fef7a10] [c000000000052c14] .memcpy_power7+0x274/0x7c4 (unreliable)
> [   18.824809] [c000001f1fef7b10] [c00000000020b874] .pcpu_free_area+0x174/0x2d0
> [   18.824813] [c000001f1fef7bb0] [c00000000020ba88] .free_percpu+0xb8/0x1b0
> [   18.824819] [c000001f1fef7c50] [c00000000043d144] .throtl_pd_exit+0x94/0xd0
> [   18.824824] [c000001f1fef7cf0] [c00000000043acf8] .blkg_free+0x88/0xe0
> [   18.824829] [c000001f1fef7d90] [c00000000018c048] .rcu_process_callbacks+0x2e8/0x8a0
> [   18.824835] [c000001f1fef7e90] [c0000000000a8ce8] .__do_softirq+0x158/0x4d0
> [   18.824840] [c000001f1fef7f90] [c000000000025ecc] .call_do_softirq+0x14/0x24
> [   18.824845] [c000000fa7483650] [c000000000010e80] .do_softirq+0x160/0x1a0
> [   18.824850] [c000000fa74836f0] [c0000000000a94a4] .irq_exit+0xf4/0x120
> [   18.824854] [c000000fa7483780] [c000000000020c44] .timer_interrupt+0x154/0x4d0
> [   18.824859] [c000000fa7483830] [c000000000003be0] decrementer_common+0x160/0x180
> [   18.824866] --- Exception: 901 at .plpar_hcall_norets+0x84/0xd4
> [   18.824866]     LR = .check_and_cede_processor+0x48/0x80
> [   18.824871] [c000000fa7483b20] [c00000000007f018] .check_and_cede_processor+0x18/0x80 (unreliable)
> [   18.824877] [c000000fa7483b90] [c00000000007f104] .dedicated_cede_loop+0x84/0x150
> [   18.824883] [c000000fa7483c50] [c0000000006bc030] .cpuidle_enter+0x30/0x50
> [   18.824887] [c000000fa7483cc0] [c0000000006bc9f4] .cpuidle_idle_call+0x104/0x720
> [   18.824892] [c000000fa7483d80] [c000000000070af8] .pSeries_idle+0x18/0x40
> [   18.824897] [c000000fa7483df0] [c000000000019084] .cpu_idle+0x1a4/0x380
> [   18.824902] [c000000fa7483ec0] [c0000000008a4c18] .start_secondary+0x520/0x528
> [   18.824907] [c000000fa7483f90] [c0000000000093f0] .start_secondary_prolog+0x10/0x14
> [   18.824911] Instruction dump:
> [   18.824914] 38840008 90030000 90e30004 38630008 7ca62850 7cc300d0 78c7e102 7cf01120
> [   18.824923] 78c60660 39200010 39400020 39600030 <7e00200c> 7c0020ce 38840010 409f001c
> [   18.824935] ---[ end trace 0bb95124affaaa45 ]---
> [   18.825046] Unrecoverable VMX/Altivec Unavailable Exception f20 at c000000000052d08
> 
> I believe the right fix is to make memcpy match usercopy and not use
> cr1.
> 
> Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>

Tested-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>

> ---
> I've not tested this fix yet, but I think it's logically correct.
> Probably needs to go to 3.6-stable as well.
> 
> diff --git a/arch/powerpc/lib/memcpy_power7.S b/arch/powerpc/lib/memcpy_power7.S
> index 7ba6c96..0663630 100644
> --- a/arch/powerpc/lib/memcpy_power7.S
> +++ b/arch/powerpc/lib/memcpy_power7.S
> @@ -239,8 +239,8 @@ _GLOBAL(memcpy_power7)
>  	ori	r9,r9,1		/* stream=1 */
> 
>  	srdi	r7,r5,7		/* length in cachelines, capped at 0x3FF */
> -	cmpldi	cr1,r7,0x3FF
> -	ble	cr1,1f
> +	cmpldi	r7,0x3FF
> +	ble	1f
>  	li	r7,0x3FF
>  1:	lis	r0,0x0E00	/* depth=7 */
>  	sldi	r7,r7,7

This change on v3.6 mainline tree allows kernel to boot without exception.

--Vaidy