Re: unrecoverable exception on G5 with CONFIG_PPC_EARLY_DEBUG enabled

quoted

Ok, the issue was introduced by the commit
caca285e5ab4a7a19fede51688106ceed6fc45dd (powerpc/mm/radix: Use
STD_MMU_64 to properly isolate hash related code) and 970mp dies on
the following condition:

quoted

+BEGIN_MMU_FTR_SECTION
        bl      slb_allocate_realmode
-
+END_MMU_FTR_SECTION_IFCLR(MMU_FTR_RADIX)

Thanks.

How did you work that out?

That FTR section says to call slb_allocate_realmode() when MMU_FTR_RADIX is
clear (ie. zero). That should always be the case on your machine, unless
you've
plugged a Power9 into your G5 ;)

quoted

In my config I've enabled radix MMU lookup but in my understanding
only recent IBM  machines support this feature and we have to call SLB
entry through slb_allocate_realmode on HPTE machine?

That's right, and that's what the code should be doing.

My G5 is booting OK:

michael@cogito:~$ uname -a
Linux cogito 4.7.0-rc3-gdb06d75 #1 SMP Thu Jun 16 05:16:31 AEST 2016 ppc64
GNU/Linux

michael@cogito:~$ cat /proc/cpuinfo
processor	: 0
cpu		: PPC970FX, altivec supported
clock		: 1599.999000MHz
revision	: 3.0 (pvr 003c 0300)

timebase	: 33333333
platform	: PowerMac
model		: PowerMac8,1
machine		: PowerMac8,1
motherboard	: PowerMac8,1 MacRISC4 Power Macintosh
detected as	: 338 (iMac G5)
pmac flags	: 00000000
L2 cache	: 512K unified
pmac-generation	: NewWorld

michael@cogito:~$ zgrep RADIX /proc/config.gz
CONFIG_PPC_RADIX_MMU=y

michael@cogito:~$ dmesg|grep _features
[    0.000000] cpu_features      = 0x0804806318100448
[    0.000000] cpu_user_features = 0xdc080000 0x00000000
[    0.000000] mmu_features      = 0x0c000001
[    0.000000] firmware_features = 0x0000000000000000

In particular notice:

#define MMU_FTR_RADIX			ASM_CONST(0x80000000)
                              mmu_features      = 0x0c000001

ie. MMU_FTR_RADIX is clear.

Do you see a different value for mmu_features?

Oops, I messed things up, sorry :/
The reason is here:
        /* All done -- return from exception. */

        ld      r10,PACA_EXSLB+EX_LR(r13)

@@ -1384,7 +1399,9 @@ slb_miss_realmode:
        lwz     r9,PACA_EXSLB+EX_CCR(r13)       /* get saved CR */

        mtlr    r10
-
+BEGIN_MMU_FTR_SECTION
+       b       2f
+END_MMU_FTR_SECTION_IFSET(MMU_FTR_RADIX)
        andi.   r10,r12,MSR_RI  /* check for unrecoverable exception */
        beq-    2f

So with the patch we got the direct jump to label 2 :
c000000000006edc <slb_miss_realmode>:
c000000000006edc:   7d 48 02 a6     mflr    r10
c000000000006ee0:   91 2d 01 8c     stw     r9,396(r13)
c000000000006ee4:   f9 4d 01 98     std     r10,408(r13)
c000000000006ee8:   48 03 28 09     bl      c0000000000396f0
<.slb_allocate_realmode>
c000000000006eec:   e9 4d 01 98     ld      r10,408(r13)
c000000000006ef0:   e8 6d 01 90     ld      r3,400(r13)
c000000000006ef4:   81 2d 01 8c     lwz     r9,396(r13)
c000000000006ef8:   7d 48 03 a6     mtlr    r10
c000000000006efc:   48 00 00 38     b       c000000000006f34
<slb_miss_realmode+0x58>
c000000000006f00:   71 8a 00 02     andi.   r10,r12,2
c000000000006f04:   41 82 00 30     beq     c000000000006f34
<slb_miss_realmode+0x58>
c000000000006f08:   7d 38 01 20     mtocrf  128,r9
c000000000006f0c:   7d 30 11 20     mtocrf  1,r9
c000000000006f10:   e9 2d 01 a8     ld      r9,424(r13)
c000000000006f14:   7d 20 e3 a6     mtppr   r9
c000000000006f18:   e9 2d 01 50     ld      r9,336(r13)
c000000000006f1c:   e9 4d 01 58     ld      r10,344(r13)
c000000000006f20:   e9 6d 01 60     ld      r11,352(r13)
c000000000006f24:   e9 8d 01 68     ld      r12,360(r13)
c000000000006f28:   e9 ad 01 70     ld      r13,368(r13)
c000000000006f2c:   4c 00 00 24     rfid
c000000000006f30:   48 00 00 00     b       c000000000006f30
<slb_miss_realmode+0x54>
c000000000006f34:   7d 7a 02 a6     mfsrr0  r11
c000000000006f38:   e9 4d 00 18     ld      r10,24(r13)
c000000000006f3c:   61 4a 6f 54     ori     r10,r10,28500
c000000000006f40:   7d 5a 03 a6     mtsrr0  r10
c000000000006f44:   e9 4d 00 20     ld      r10,32(r13)
c000000000006f48:   7d 5b 03 a6     mtsrr1  r10
c000000000006f4c:   4c 00 00 24     rfid
c000000000006f50:   48 00 00 00     b       c000000000006f50
<slb_miss_realmode+0x74>

Without the ftr conditional section everything looks fine:
c000000000006edc <slb_miss_realmode>:
c000000000006edc:   7d 48 02 a6     mflr    r10
c000000000006ee0:   91 2d 01 8c     stw     r9,396(r13)
c000000000006ee4:   f9 4d 01 98     std     r10,408(r13)
c000000000006ee8:   48 03 28 09     bl      c0000000000396f0
<.slb_allocate_realmode>
c000000000006eec:   e9 4d 01 98     ld      r10,408(r13)
c000000000006ef0:   e8 6d 01 90     ld      r3,400(r13)
c000000000006ef4:   81 2d 01 8c     lwz     r9,396(r13)
c000000000006ef8:   7d 48 03 a6     mtlr    r10
c000000000006efc:   71 8a 00 02     andi.   r10,r12,2
c000000000006f00:   41 82 00 30     beq     c000000000006f30
<slb_miss_realmode+0x54>
c000000000006f04:   7d 38 01 20     mtocrf  128,r9
c000000000006f08:   7d 30 11 20     mtocrf  1,r9
c000000000006f0c:   e9 2d 01 a8     ld      r9,424(r13)
c000000000006f10:   7d 20 e3 a6     mtppr   r9
c000000000006f14:   e9 2d 01 50     ld      r9,336(r13)
c000000000006f18:   e9 4d 01 58     ld      r10,344(r13)
c000000000006f1c:   e9 6d 01 60     ld      r11,352(r13)
c000000000006f20:   e9 8d 01 68     ld      r12,360(r13)
c000000000006f24:   e9 ad 01 70     ld      r13,368(r13)
c000000000006f28:   4c 00 00 24     rfid
c000000000006f2c:   48 00 00 00     b       c000000000006f2c
<slb_miss_realmode+0x50>
c000000000006f30:   7d 7a 02 a6     mfsrr0  r11
c000000000006f34:   e9 4d 00 18     ld      r10,24(r13)
c000000000006f38:   61 4a 6f 50     ori     r10,r10,28496
c000000000006f3c:   7d 5a 03 a6     mtsrr0  r10
c000000000006f40:   e9 4d 00 20     ld      r10,32(r13)
c000000000006f44:   7d 5b 03 a6     mtsrr1  r10
c000000000006f48:   4c 00 00 24     rfid
c000000000006f4c:   48 00 00 00     b       c000000000006f4c
<slb_miss_realmode+0x70>

cheers