[PATCH] powerpc, xmon: Enable hardware instruction breakpoint support on POWER8
Anshuman Khandual
khandual at linux.vnet.ibm.com
Wed Jun 4 18:48:33 EST 2014
On 06/03/2014 11:33 AM, Anshuman Khandual wrote:
> On 05/30/2014 07:12 PM, Aneesh Kumar K.V wrote:
>> > Anshuman Khandual <khandual at linux.vnet.ibm.com> writes:
>> >
>>> >> This patch enables support for hardware instruction breakpoints on POWER8 with
>>> >> the help of a new register called CIABR (Completed Instruction Address Breakpoint
>>> >> Register). With this patch, single hardware instruction breakpoint can be added
>>> >> and cleared during any active xmon debug session. This hardware based instruction
>>> >> breakpoint mechanism works correctly along with the existing TRAP based instruction
>>> >> breakpoints available on xmon. Example usage as follows.
>>> >>
>>> >> (A) Start xmon:
>>> >> $echo x > /proc/sysrq-trigger
>>> >> SysRq : Entering xmon
>>> >> cpu 0x0: Vector: 0 at [c000001f6c67f960]
>>> >> pc: c000000000072078: .sysrq_handle_xmon+0x58/0x60
>>> >> lr: c000000000072078: .sysrq_handle_xmon+0x58/0x60
>>> >> sp: c000001f6c67fac0
>>> >> msr: 9000000000009032
>>> >> current = 0xc000001f6e709ac0
>>> >> paca = 0xc00000000fffa000 softe: 0 irq_happened: 0x00
>>> >> pid = 3250, comm = bash
>>> >> enter ? for help
>>> >> 0:mon> b
>>> >> type address
>>> >>
>>> >> (B) Set the breakpoint:
>>> >> 0:mon> ls .power_pmu_add
>>> >> .power_pmu_add: c000000000078f50
>>> >> 0:mon> bi c000000000078f50
>>> >> 0:mon> b
>>> >> type address
>>> >> 1 inst c000000000078f50 .power_pmu_add+0x0/0x2e0
>>> >> 0:mon> ls .perf_event_interrupt
>>> >> .perf_event_interrupt: c00000000007aee0
>>> >> 0:mon> bi c00000000007aee0
>>> >> One instruction breakpoint possible with CIABR
>>> >> 0:mon> x
>>> >>
>>> >> (C) Run the workload (with the breakpoint):
>>> >> $./perf record ls
>>> >> cpu 0x2: Vector: d00 (Single Step) at [c000001f718133a0]
>>> >> pc: c000000000078f54: .power_pmu_add+0x4/0x2e0
>>> >> lr: c000000000155be0: .event_sched_in+0x90/0x1d0
>>> >> sp: c000001f71813620
>>> >> msr: 9000000040109032
>>> >> current = 0xc000001f6ce30000
>>> >> paca = 0xc00000000fffa600 softe: 0 irq_happened: 0x01
>>> >> pid = 3270, comm = ls
>>> >> std r22,-80(r1)
>>> >> enter ? for help
>>> >>
>>> >> (D) Clear the breakpoint:
>>> >> 2:mon> bc
>>> >> All breakpoints cleared
>>> >> 2:mon> x
>>> >> [ perf record: Woken up 1 times to write data ]
>>> >> [ perf record: Captured and wrote 0.002 MB perf.data (~66 samples) ]
>>> >>
>>> >> (E) Run the workload again (without any breakpoints):
>>> >> $./perf record ls
>>> >> [ perf record: Woken up 1 times to write data ]
>>> >> [ perf record: Captured and wrote 0.001 MB perf.data (~61 samples) ]
>>> >>
>>> >> Signed-off-by: Anshuman Khandual <khandual at linux.vnet.ibm.com>
>>> >> ---
>>> >> arch/powerpc/xmon/xmon.c | 62 ++++++++++++++++++++++++++++++++++++++++++++----
>>> >> 1 file changed, 58 insertions(+), 4 deletions(-)
>>> >>
>>> >> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
>>> >> index 3fd1d9a..f74ec83 100644
>>> >> --- a/arch/powerpc/xmon/xmon.c
>>> >> +++ b/arch/powerpc/xmon/xmon.c
>>> >> @@ -48,6 +48,7 @@
>>> >> #ifdef CONFIG_PPC64
>>> >> #include <asm/hvcall.h>
>>> >> #include <asm/paca.h>
>>> >> +#include <asm/plpar_wrappers.h>
>>> >> #endif
>>> >>
>>> >> #include "nonstdio.h"
>>> >> @@ -89,6 +90,7 @@ struct bpt {
>>> >> /* Bits in bpt.enabled */
>>> >> #define BP_IABR_TE 1 /* IABR translation enabled */
>>> >> #define BP_IABR 2
>>> >> +#define BP_CIABR 4
>>> >> #define BP_TRAP 8
>>> >> #define BP_DABR 0x10
>>> >>
>>> >> @@ -97,6 +99,7 @@ static struct bpt bpts[NBPTS];
>>> >> static struct bpt dabr;
>>> >> static struct bpt *iabr;
>>> >> static unsigned bpinstr = 0x7fe00008; /* trap */
>>> >> +static bool ciabr_used = false; /* CIABR instruction breakpoint */
>>> >>
>>> >> #define BP_NUM(bp) ((bp) - bpts + 1)
>>> >>
>>> >> @@ -269,6 +272,34 @@ static inline void cinval(void *p)
>>> >> asm volatile ("dcbi 0,%0; icbi 0,%0" : : "r" (p));
>>> >> }
>>> >>
>>> >> +static void write_ciabr(unsigned long ciabr)
>>> >> +{
>>> >> + if (cpu_has_feature(CPU_FTR_HVMODE)) {
>>> >> + mtspr(SPRN_CIABR, ciabr);
>>> >> + return;
>>> >> + }
>>> >> +
>>> >> +#ifdef CONFIG_PPC64
>>> >> + plapr_set_ciabr(ciabr);
>>> >> +#endif
>>> >> +}
>>> >> +
>>> >> +static void set_ciabr(unsigned long addr)
>>> >> +{
>>> >> + addr &= ~CIABR_PRIV;
>>> >> + if (cpu_has_feature(CPU_FTR_HVMODE))
>>> >> + addr |= CIABR_PRIV_HYPER;
>>> >> + else
>>> >> + addr |= CIABR_PRIV_SUPER;
>>> >> + write_ciabr(addr);
>>> >> +}
>>> >> +
>>> >> +static void clear_ciabr(void)
>>> >> +{
>>> >> + if (cpu_has_feature(CPU_FTR_ARCH_207S))
>>> >> + write_ciabr(0);
>>> >> +}
>>> >> +
>>> >> /*
>>> >> * Disable surveillance (the service processor watchdog function)
>>> >> * while we are in xmon.
>>> >> @@ -764,6 +795,9 @@ static void insert_cpu_bpts(void)
>>> >> if (iabr && cpu_has_feature(CPU_FTR_IABR))
>>> >> mtspr(SPRN_IABR, iabr->address
>>> >> | (iabr->enabled & (BP_IABR|BP_IABR_TE)));
>>> >> +
>>> >> + if (iabr && cpu_has_feature(CPU_FTR_ARCH_207S))
>>> >> + set_ciabr(iabr->address);
>>> >> }
>>> >>
>>> >> static void remove_bpts(void)
>>> >> @@ -791,6 +825,7 @@ static void remove_cpu_bpts(void)
>>> >> hw_breakpoint_disable();
>>> >> if (cpu_has_feature(CPU_FTR_IABR))
>>> >> mtspr(SPRN_IABR, 0);
>>> >> + clear_ciabr();
>>> >> }
>>> >>
>>> >> /* Command interpreting routine */
>>> >> @@ -1124,7 +1159,7 @@ static char *breakpoint_help_string =
>>> >> "b <addr> [cnt] set breakpoint at given instr addr\n"
>>> >> "bc clear all breakpoints\n"
>>> >> "bc <n/addr> clear breakpoint number n or at addr\n"
>>> >> - "bi <addr> [cnt] set hardware instr breakpoint (POWER3/RS64 only)\n"
>>> >> + "bi <addr> [cnt] set hardware instr breakpoint (POWER3/RS64/POWER8 only)\n"
>>> >> "bd <addr> [cnt] set hardware data breakpoint\n"
>>> >> "";
>>> >>
>>> >> @@ -1163,11 +1198,20 @@ bpt_cmds(void)
>>> >> break;
>>> >>
>>> >> case 'i': /* bi - hardware instr breakpoint */
>>> >> - if (!cpu_has_feature(CPU_FTR_IABR)) {
>>> >> + if (!cpu_has_feature(CPU_FTR_IABR) && !cpu_has_feature(CPU_FTR_ARCH_207S)) {
>>> >> printf("Hardware instruction breakpoint "
>>> >> "not supported on this cpu\n");
>>> >> break;
>>> >> }
>>> >> +
>>> >> + if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
>>> >> + if (ciabr_used) {
>>> >> + printf("One instruction breakpoint "
>>> >> + "possible with CIABR\n");
>>> >> + break;
>>> >> + }
>> >
>> > We don't seem to do that with iabr ? Why keep ciabr different
> Right now with the IABR implementation if we try to set hardware instruction
> breakpoint while one is already there, it just get overridden with the new
> address without complaining. I thought with this at least for CIABR cases,
> it will complain about it and require the user to clear the breakpoint
> explicitly before allowing a new breakpoint. Okay will remove this.
>
I tried removing the "ciabr_used" variable and all related checks/assignments on it.
Then I was able to add all these three address as hardware instruction breakpoint
and xmon never complained that it might override the existing actual checkpoint
implemented with CIABR. It accepted all the three addresses which can later be
listed as below.
0:mon> b
type address
1 inst c0000000000830d0 .power_pmu_add+0x0/0x2e0
2 inst c000000000084690 .power_pmu_del+0x0/0x3a0
3 inst c000000000085060 .perf_event_interrupt+0x0/0x480
But in reality, only perf_event_interrupt function's address got written into CIABR
register and got triggered with the workload. I dont have a system which has IABR
support to test it's behaviour for this situation. But this does not sound okay,
we should explicitly inform the user that the hardware instruction breakpoint has
been overridden with the latest command or reject the attempt. Looking for some
suggestions in this regard. Thank you.
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