Re: [PATCH] arm64: hwpoison: add VM_FAULT_HWPOISON[_LARGE] handling

[Punit Agrawal]

On 06/02/17 22:21, Baicar, Tyler wrote:
> Hello Punit,
>
>
> On 2/3/2017 9:17 AM, Punit Agrawal wrote:
> > Tyler Baicar <tbaicar@xxxxxxxxxxxxxx> writes:
> >
> > > From: "Jonathan (Zhixiong) Zhang" <zjzhang@xxxxxxxxxxxxxx>
> > >
> > > Add VM_FAULT_HWPOISON[_LARGE] handling to the arm64 page fault
> > > handler. Handling of VM_FAULT_HWPOISON[_LARGE] is very similar
> > > to VM_FAULT_OOM, the only difference is that a different si_code
> > > (BUS_MCEERR_AR) is passed to user space and si_addr_lsb field is
> > > initialized.
> > >
> > > Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@xxxxxxxxxxxxxx>
> > > Signed-off-by: Tyler Baicar <tbaicar@xxxxxxxxxxxxxx>
> > > ---
> > >  arch/arm64/mm/fault.c | 31 +++++++++++++++++++++++++++----
> > >  1 file changed, 27 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > [...]
> >
> > > @@ -426,7 +439,17 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
> > >              */
> > >             sig = SIGBUS;
> > >             code = BUS_ADRERR;
> > > -   } else {
> > > +   }
> > > +#ifdef CONFIG_MEMORY_FAILURE
> > > +   else if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
> > Please add spaces around '|'.
> Will do!
> > > +           pr_err(
> > > +   "Killing %s:%d due to hardware memory corruption fault at %lx\n",
> > > +                   tsk->comm, tsk->pid, addr);
> > The message is misleading as we're not really killing a task but
> > delivering a signal (SIGBUS) which might not always lead to the receiver
> > being killed.
> >
> > But considering that we don't print any message for the other faults,
> > I'd prefer that we drop this pr_err.
> Yes, I'll drop the pr_err.
> > > +           sig = SIGBUS;
> > > +           code = BUS_MCEERR_AR;
> > > +   }
> > > +#endif
> > Although to get a HWPOISON fault CONFIG_MEMORY_FAILURE is needed, the
> > handling seems safe even when it is not enabled. Can the ifdeffery be
> > dropped?
> Yes, I can drop the ifdef. The handling would be fine either way.
> > Also, I was wondering how this code was tested? Did you by any chance
> > try using hwpoison inject debugfs interface?
> This was originally tested using proprietary error injection that we have.
>
> I just tried the hwpoison inject interface and it didn't result in
> hitting this code path.
>
> [   70.747697] Injecting memory failure at pfn 0x400340
>
> [   70.748547] Memory failure: 0x400340: Unknown page state
>
> [   70.752911] Memory failure: 0x400340: unknown page still referenced
> by 1 users
>
> [   70.760167] Memory failure: 0x400340: recovery action for unknown
> page: Failed
>
>
> I've never used hwpoison inject though, so maybe I'm doing something
> wrong :)

No worries. Writing the pfn an executable is loaded at
/sys/kernel/debug/hwpoison/corrupt-pfn triggered the code for me. On my
system the program dies after printing "Bus error" - probably what the
default handler from glibc is configured to do in this situation. :)

> Thanks,
> Tyler
>
> --
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project.
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