linux-kernel - Re: [PATCH v4 0/5] Powerpc/Watchpoint: Few important fixes

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Date:   Sat, 12 Oct 2019 09:31:41 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     mpe@...erman.id.au, mikey@...ling.org, npiggin@...il.com,
        benh@...nel.crashing.org, paulus@...ba.org,
        naveen.n.rao@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/5] Powerpc/Watchpoint: Few important fixes



Le 10/10/2019 à 08:25, Ravi Bangoria a écrit :
> 
> 
> On 10/10/19 10:14 AM, Ravi Bangoria wrote:
>>
>>>> @Christophe, Is patch5 works for you on 8xx?
>>>>
>>>
>>> Getting the following :
>>>
>>> root@...ip:~# ./ptrace-hwbreak
>>> test: ptrace-hwbreak
>>> tags: git_version:v5.4-rc2-710-gf0082e173fe4-dirty
>>> PTRACE_SET_DEBUGREG, WO, len: 1: Ok
>>> PTRACE_SET_DEBUGREG, WO, len: 2: Ok
>>> PTRACE_SET_DEBUGREG, WO, len: 4: Ok
>>> PTRACE_SET_DEBUGREG, WO, len: 8: Ok
>>> PTRACE_SET_DEBUGREG, RO, len: 1: Ok
>>> PTRACE_SET_DEBUGREG, RO, len: 2: Ok
>>> PTRACE_SET_DEBUGREG, RO, len: 4: Ok
>>> PTRACE_SET_DEBUGREG, RO, len: 8: Ok
>>> PTRACE_SET_DEBUGREG, RW, len: 1: Ok
>>> PTRACE_SET_DEBUGREG, RW, len: 2: Ok
>>> PTRACE_SET_DEBUGREG, RW, len: 4: Ok
>>> PTRACE_SET_DEBUGREG, RW, len: 8: Ok
>>> PPC_PTRACE_SETHWDEBUG, MODE_EXACT, WO, len: 1: Ok
>>> PPC_PTRACE_SETHWDEBUG, MODE_EXACT, RO, len: 1: Ok
>>> PPC_PTRACE_SETHWDEBUG, MODE_EXACT, RW, len: 1: Ok
>>> PPC_PTRACE_SETHWDEBUG, MODE_RANGE, DW ALIGNED, WO, len: 6: Ok
>>> PPC_PTRACE_SETHWDEBUG, MODE_RANGE, DW ALIGNED, RO, len: 6: Fail
>>> failure: ptrace-hwbreak
>>>
>>
>> Thanks Christophe. I don't have any 8xx box. I checked qemu and it seems
>> qemu emulation for 8xx is not yet supported. So I can't debug this. Can
>> you please check why it's failing?
> 
> PPC_PTRACE_SETHWDEBUG internally uses DAWR register and probably 8xx does
> not emulate DAWR logic, it only uses DABR to emulate double-word 
> watchpoint.
> In that case, all testcases that uses PPC_PTRACE_SETHWDEBUG should be
> disabled for 8xx. I'll change [PATCH 5] accordingly and resend.

I think the MODE_EXACT ones are OK with the 8xx at the time being.

> 
> Also, do you think I should fix hw_breakpoint_validate_len() from [PARCH 1]
> for 8xx? I re-checked you recent patch* to allow any address range size for
> 8xx. With that patch, hw_breakpoint_validate_len() won't get called at all
> for 8xx.

At the time being, the 8xx emulates DABR so it has the same limitations 
as BOOK3S.
My patch needs to be rebased on top of your series and I think it needs 
some modifications, as it seems it doesn't properly handle size 1 and 
size 2 breakpoints at least.
So I think that you should leave your Patch1 as is, and I'll modify the 
validate_len() logic while rebasing my patch.

Christophe