Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Ravi Bangoria]

On Sunday 06 November 2016 01:01 AM, Anton Blanchard wrote:
> Hi,
>
>> kprobe, uprobe, hw-breakpoint and xmon are the only user of
>> emulate_step.
>>
>> Kprobe / uprobe single-steps instruction if they can't emulate it, so
>> there is no problem with them. As I mention, hw-breakpoint is broken.
>> However I'm not sure about xmon, I need to check that.
> I was mostly concerned that it would impact kprobes. Sounds like we are
> ok there.
>
>> So yes, there is no user-visible feature that depends on this.
> Aren't hardware breakpoints exposed via perf? I'd call perf
> user-visible.


Thanks Anton, That's a good catch. I tried this on ppc64le:

  $ sudo cat /proc/kallsyms  | grep pid_max
c116998c D pid_max

  $ sudo ./perf record -a --event=mem:0xc116998c sleep 10


Before patch:
  It does not record any data and throws below warning.

  $ dmesg
[  817.895573] Unable to handle hardware breakpoint. Breakpoint at 
0xc116998c will be disabled.
[  817.895581] [ cut here ]
[  817.895588] WARNING: CPU: 24 PID: 2032 at 
arch/powerpc/kernel/hw_breakpoint.c:277 hw_breakpoint_handler+0x124/0x230
...

After patch:
  It records data properly.

  $ sudo ./perf report --stdio
...
# Samples: 36  of event 'mem:0xc116998c'
# Event count (approx.): 36
#
# Overhead  CommandShared Object Symbol  
#   .    .
#
63.89%  kdumpctl   [kernel.vmlinux]  [k] alloc_pid
27.78%  opal_errd  [kernel.vmlinux]  [k] alloc_pid
 5.56%  kworker/u97:4  [kernel.vmlinux]  [k] alloc_pid
 2.78%  systemd[kernel.vmlinux]  [k] alloc_pid


-Ravi

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Anton Blanchard]

Hi,

> kprobe, uprobe, hw-breakpoint and xmon are the only user of
> emulate_step.
> 
> Kprobe / uprobe single-steps instruction if they can't emulate it, so
> there is no problem with them. As I mention, hw-breakpoint is broken.
> However I'm not sure about xmon, I need to check that.

I was mostly concerned that it would impact kprobes. Sounds like we are
ok there.

> So yes, there is no user-visible feature that depends on this.

Aren't hardware breakpoints exposed via perf? I'd call perf
user-visible.

Anton

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Ravi Bangoria]

On Friday 04 November 2016 07:37 AM, Andrew Donnellan wrote:
> On 03/11/16 21:27, Ravi Bangoria wrote:
>> Yes, kernel-space hw-breakpoint feature is broken on LE without this.
>
> Is there any actual user-visible feature that depends on this, or is this 
> solely for debugging and development purposes?
>
> It would of course be *nice* to have it in stable trees (particularly so we 
> pick it up in distros) but I'm not convinced that enabling HW breakpoints on 
> a platform where it has *never* worked qualifies as an "actual bug".
>
> (BTW many thanks for fixing this - I had a shot at it late last year but 
> never quite got there!)

Thanks Andrew,

kprobe, uprobe, hw-breakpoint and xmon are the only user of emulate_step.

Kprobe / uprobe single-steps instruction if they can't emulate it, so there
is no problem with them. As I mention, hw-breakpoint is broken. However
I'm not sure about xmon, I need to check that.

So yes, there is no user-visible feature that depends on this.

-Ravi

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Andrew Donnellan]

On 03/11/16 21:27, Ravi Bangoria wrote:

Yes, kernel-space hw-breakpoint feature is broken on LE without this.


Is there any actual user-visible feature that depends on this, or is 
this solely for debugging and development purposes?


It would of course be *nice* to have it in stable trees (particularly so 
we pick it up in distros) but I'm not convinced that enabling HW 
breakpoints on a platform where it has *never* worked qualifies as an 
"actual bug".


(BTW many thanks for fixing this - I had a shot at it late last year but 
never quite got there!)


--
Andrew Donnellan  OzLabs, ADL Canberra
andrew.donnel...@au1.ibm.com  IBM Australia Limited

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Ravi Bangoria]

On Thursday 03 November 2016 03:18 PM, Michael Ellerman wrote:
> Ravi Bangoria  writes:
>
>> On Thursday 03 November 2016 02:34 AM, Anton Blanchard wrote:
>>> Hi Ravi,
>>>
 emulate_step() uses a number of underlying kernel functions that were
 initially not enabled for LE. This has been rectified since. So, fix
 emulate_step() for LE for the corresponding instructions.
>>> Thanks. Should this be queued up for stable?
>> Thanks Anton. Yes, this should go in stable.
> It's fairly big for stable. Does it fix an actual bug? If so what, and
> how bad is it, what's the user impact.

Hi Michael,

Yes, kernel-space hw-breakpoint feature is broken on LE without this.

Actually, there is no specific commit that introduced this. Back
in 2010, Paul Mackerras has added emulation support for load/store
instructions for BE. hw-breakpoint was also develpoed by K.Prasad
in the same timeframe.

Kernel-space hw-breakpoint emulates causative instruction before
notifying to user. As emulate_step is never enabled for LE, kernel-
space hw-breakpoint is always broken on LE.

-Ravi

> Can you also pinpoint which commit it "fixes"?
>
> cheers
>

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Michael Ellerman]

Ravi Bangoria  writes:

> On Thursday 03 November 2016 02:34 AM, Anton Blanchard wrote:
>> Hi Ravi,
>>
>>> emulate_step() uses a number of underlying kernel functions that were
>>> initially not enabled for LE. This has been rectified since. So, fix
>>> emulate_step() for LE for the corresponding instructions.
>> Thanks. Should this be queued up for stable?
>
> Thanks Anton. Yes, this should go in stable.

It's fairly big for stable. Does it fix an actual bug? If so what, and
how bad is it, what's the user impact.

Can you also pinpoint which commit it "fixes"?

cheers

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Ravi Bangoria]

On Thursday 03 November 2016 02:34 AM, Anton Blanchard wrote:
> Hi Ravi,
>
>> emulate_step() uses a number of underlying kernel functions that were
>> initially not enabled for LE. This has been rectified since. So, fix
>> emulate_step() for LE for the corresponding instructions.
> Thanks. Should this be queued up for stable?

Thanks Anton. Yes, this should go in stable.

-Ravi

Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Anton Blanchard]

Hi Ravi,

> emulate_step() uses a number of underlying kernel functions that were
> initially not enabled for LE. This has been rectified since. So, fix
> emulate_step() for LE for the corresponding instructions.

Thanks. Should this be queued up for stable?

Anton

> Reported-by: Anton Blanchard 
> Signed-off-by: Ravi Bangoria 
> ---
>  arch/powerpc/lib/sstep.c | 20 
>  1 file changed, 20 deletions(-)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index 3362299..6ca3b90 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -1807,8 +1807,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) goto instr_done;
>  
>   case LARX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   if (op.ea & (size - 1))
>   break;  /* can't handle
> misaligned */ err = -EFAULT;
> @@ -1832,8 +1830,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) goto ldst_done;
>  
>   case STCX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   if (op.ea & (size - 1))
>   break;  /* can't handle
> misaligned */ err = -EFAULT;
> @@ -1859,8 +1855,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) goto ldst_done;
>  
>   case LOAD:
> - if (regs->msr & MSR_LE)
> - return 0;
>   err = read_mem(>gpr[op.reg], op.ea, size,
> regs); if (!err) {
>   if (op.type & SIGNEXT)
> @@ -1872,8 +1866,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) 
>  #ifdef CONFIG_PPC_FPU
>   case LOAD_FP:
> - if (regs->msr & MSR_LE)
> - return 0;
>   if (size == 4)
>   err = do_fp_load(op.reg, do_lfs, op.ea,
> size, regs); else
> @@ -1882,15 +1874,11 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) #endif
>  #ifdef CONFIG_ALTIVEC
>   case LOAD_VMX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   err = do_vec_load(op.reg, do_lvx, op.ea & ~0xfUL,
> regs); goto ldst_done;
>  #endif
>  #ifdef CONFIG_VSX
>   case LOAD_VSX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   err = do_vsx_load(op.reg, do_lxvd2x, op.ea, regs);
>   goto ldst_done;
>  #endif
> @@ -1913,8 +1901,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) goto instr_done;
>  
>   case STORE:
> - if (regs->msr & MSR_LE)
> - return 0;
>   if ((op.type & UPDATE) && size == sizeof(long) &&
>   op.reg == 1 && op.update_reg == 1 &&
>   !(regs->msr & MSR_PR) &&
> @@ -1927,8 +1913,6 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) 
>  #ifdef CONFIG_PPC_FPU
>   case STORE_FP:
> - if (regs->msr & MSR_LE)
> - return 0;
>   if (size == 4)
>   err = do_fp_store(op.reg, do_stfs, op.ea,
> size, regs); else
> @@ -1937,15 +1921,11 @@ int __kprobes emulate_step(struct pt_regs
> *regs, unsigned int instr) #endif
>  #ifdef CONFIG_ALTIVEC
>   case STORE_VMX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   err = do_vec_store(op.reg, do_stvx, op.ea & ~0xfUL,
> regs); goto ldst_done;
>  #endif
>  #ifdef CONFIG_VSX
>   case STORE_VSX:
> - if (regs->msr & MSR_LE)
> - return 0;
>   err = do_vsx_store(op.reg, do_stxvd2x, op.ea, regs);
>   goto ldst_done;
>  #endif

[PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

[Ravi Bangoria]

emulate_step() uses a number of underlying kernel functions that were
initially not enabled for LE. This has been rectified since. So, fix
emulate_step() for LE for the corresponding instructions.

Reported-by: Anton Blanchard 
Signed-off-by: Ravi Bangoria 
---
 arch/powerpc/lib/sstep.c | 20 
 1 file changed, 20 deletions(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 3362299..6ca3b90 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1807,8 +1807,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
goto instr_done;
 
case LARX:
-   if (regs->msr & MSR_LE)
-   return 0;
if (op.ea & (size - 1))
break;  /* can't handle misaligned */
err = -EFAULT;
@@ -1832,8 +1830,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
goto ldst_done;
 
case STCX:
-   if (regs->msr & MSR_LE)
-   return 0;
if (op.ea & (size - 1))
break;  /* can't handle misaligned */
err = -EFAULT;
@@ -1859,8 +1855,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
goto ldst_done;
 
case LOAD:
-   if (regs->msr & MSR_LE)
-   return 0;
err = read_mem(>gpr[op.reg], op.ea, size, regs);
if (!err) {
if (op.type & SIGNEXT)
@@ -1872,8 +1866,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
 
 #ifdef CONFIG_PPC_FPU
case LOAD_FP:
-   if (regs->msr & MSR_LE)
-   return 0;
if (size == 4)
err = do_fp_load(op.reg, do_lfs, op.ea, size, regs);
else
@@ -1882,15 +1874,11 @@ int __kprobes emulate_step(struct pt_regs *regs, 
unsigned int instr)
 #endif
 #ifdef CONFIG_ALTIVEC
case LOAD_VMX:
-   if (regs->msr & MSR_LE)
-   return 0;
err = do_vec_load(op.reg, do_lvx, op.ea & ~0xfUL, regs);
goto ldst_done;
 #endif
 #ifdef CONFIG_VSX
case LOAD_VSX:
-   if (regs->msr & MSR_LE)
-   return 0;
err = do_vsx_load(op.reg, do_lxvd2x, op.ea, regs);
goto ldst_done;
 #endif
@@ -1913,8 +1901,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
goto instr_done;
 
case STORE:
-   if (regs->msr & MSR_LE)
-   return 0;
if ((op.type & UPDATE) && size == sizeof(long) &&
op.reg == 1 && op.update_reg == 1 &&
!(regs->msr & MSR_PR) &&
@@ -1927,8 +1913,6 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned 
int instr)
 
 #ifdef CONFIG_PPC_FPU
case STORE_FP:
-   if (regs->msr & MSR_LE)
-   return 0;
if (size == 4)
err = do_fp_store(op.reg, do_stfs, op.ea, size, regs);
else
@@ -1937,15 +1921,11 @@ int __kprobes emulate_step(struct pt_regs *regs, 
unsigned int instr)
 #endif
 #ifdef CONFIG_ALTIVEC
case STORE_VMX:
-   if (regs->msr & MSR_LE)
-   return 0;
err = do_vec_store(op.reg, do_stvx, op.ea & ~0xfUL, regs);
goto ldst_done;
 #endif
 #ifdef CONFIG_VSX
case STORE_VSX:
-   if (regs->msr & MSR_LE)
-   return 0;
err = do_vsx_store(op.reg, do_stxvd2x, op.ea, regs);
goto ldst_done;
 #endif
-- 
1.8.3.1