Re: PowerNV decrementer fails to fire

[Cédric Le Goater]

Hello Anton,

On 24/10/2019 00:04, Anton Blanchard wrote:
> Hi,
> 
> Mikey and I noticed that the decrementer isn't firing when
> it should. If a decrementer is pending and an mtmsrd(MSR_EE) is
> executed then we should take the decrementer exception. From the PPC AS:
> 
>   If MSR EE = 0 and an External, Decrementer, or Per-
>   formance Monitor exception is pending, executing
>   an mtmsrd instruction that sets MSR EE to 1 will
>   cause the interrupt to occur before the next instruc-
>   tion is executed, if no higher priority exception
>   exists

I suppose we are missing a test on MSR_EE in the store helper routine 
of MSR to generate the exception ? See helper_store_msr() and 
hreg_store_msr().


C.






> 
> A test case is below. r31 is incremented for every decrementer
> exception.
> 
> powerpc64le-linux-gcc -c test.S
> powerpc64le-linux-ld -Ttext=0x0 -o test.elf test.o
> powerpc64le-linux-objcopy -O binary test.elf test.bin
> 
> r31 never moves. If I build with:
> 
> powerpc64le-linux-gcc -DFIX_BROKEN -c test.S
> 
> I see r31 move.
> 
> Thanks,
> Anton
> --
> 
> #include <ppc-asm.h>
> 
> /* Load an immediate 64-bit value into a register */
> #define LOAD_IMM64(r, e)                      \
>       lis     r,(e)@highest;                  \
>       ori     r,r,(e)@higher;                 \
>       rldicr  r,r, 32, 31;                    \
>       oris    r,r, (e)@h;                     \
>       ori     r,r, (e)@l;
> 
> #define FIXUP_ENDIAN                                             \
>       tdi   0,0,0x48;   /* Reverse endian of b . + 8          */ \
>       b     191f;       /* Skip trampoline if endian is good  */ \
>       .long 0xa600607d; /* mfmsr r11                          */ \
>       .long 0x01006b69; /* xori r11,r11,1                     */ \
>       .long 0x05009f42; /* bcl 20,31,$+4                      */ \
>       .long 0xa602487d; /* mflr r10                           */ \
>       .long 0x14004a39; /* addi r10,r10,20                    */ \
>       .long 0xa64b5a7d; /* mthsrr0 r10                        */ \
>       .long 0xa64b7b7d; /* mthsrr1 r11                        */ \
>       .long 0x2402004c; /* hrfid                              */ \
> 191:
> 
>       .= 0x0
> .globl _start
> _start:
>       b       1f
> 
>       .= 0x10
>       FIXUP_ENDIAN
>       b       1f
> 
>       .= 0x100
> 1:
>       FIXUP_ENDIAN
>       b       __initialize
> 
> #define EXCEPTION(nr)         \
>       .= nr                   ;\
>       b       .
> 
>       /* More exception stubs */
>       EXCEPTION(0x300)
>       EXCEPTION(0x380)
>       EXCEPTION(0x400)
>       EXCEPTION(0x480)
>       EXCEPTION(0x500)
>       EXCEPTION(0x600)
>       EXCEPTION(0x700)
>       EXCEPTION(0x800)
> 
>       .= 0x900
>       LOAD_IMM64(r0, 0x1000000)
>       mtdec   r0
>       addi    r31,r31,1
>       rfid
> 
>       EXCEPTION(0x980)
>       EXCEPTION(0xa00)
>       EXCEPTION(0xb00)
>       EXCEPTION(0xc00)
>       EXCEPTION(0xd00)
>       EXCEPTION(0xe00)
>       EXCEPTION(0xe20)
>       EXCEPTION(0xe40)
>       EXCEPTION(0xe60)
>       EXCEPTION(0xe80)
>       EXCEPTION(0xf00)
>       EXCEPTION(0xf20)
>       EXCEPTION(0xf40)
>       EXCEPTION(0xf60)
>       EXCEPTION(0xf80)
>       EXCEPTION(0x1000)
>       EXCEPTION(0x1100)
>       EXCEPTION(0x1200)
>       EXCEPTION(0x1300)
>       EXCEPTION(0x1400)
>       EXCEPTION(0x1500)
>       EXCEPTION(0x1600)
> 
> __initialize:
>       /* SF, HV, EE, RI, LE */
>       LOAD_IMM64(r0, 0x9000000000008003)
>       mtmsrd  r0
> 
>       LOAD_IMM64(r0, 0x1000000)
>       mtdec r0
> 
> 1:    LOAD_IMM64(r30,0x8000)
>       mtmsrd  r30,1
> 
>       /* We should take the decrementer here */
> #ifdef FIX_BROKEN
>       LOAD_IMM64(r29,0x100000000)
>       mtctr   r29
> 2:    bdnz    2b
> #endif
> 
>       li      r30,0x0
>       mtmsrd  r30,1
>       b       1b
>