linux-kernel - Re: [PATCH] riscv: code patching only works on !XIP

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Message-ID: <20210608161457.192b3ca3@xhacker.debian>
Date:   Tue, 8 Jun 2021 16:14:57 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Vitaly Wool <vitaly.wool@...sulko.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Jisheng Zhang <jszhang3@...l.ustc.edu.cn>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: code patching only works on !XIP_KERNEL

On Tue, 8 Jun 2021 09:50:00 +0200
Vitaly Wool <vitaly.wool@...sulko.com> wrote:


> 
> 
> Hi Jisheng,
> 
> On Tue, Jun 8, 2021 at 9:24 AM Jisheng Zhang
> <Jisheng.Zhang@...aptics.com> wrote:
> >
> > On Mon, 24 May 2021 21:32:38 +0200
> > Vitaly Wool <vitaly.wool@...sulko.com> wrote:
> >
> >  
> > >
> > >
> > > On Sat, May 22, 2021 at 7:15 PM Palmer Dabbelt <palmer@...belt.com> wrote:  
> > > >
> > > > On Mon, 10 May 2021 11:19:30 PDT (-0700), vitaly.wool@...sulko.com wrote:  
> > > > > On Mon, May 10, 2021 at 6:35 PM Jisheng Zhang <jszhang3@...l.ustc.edu.cn> wrote:  
> > > > >>
> > > > >> From: Jisheng Zhang <jszhang@...nel.org>
> > > > >>
> > > > >> Some features which need code patching such as KPROBES, DYNAMIC_FTRACE
> > > > >> KGDB can only work on !XIP_KERNEL. Add dependencies for these features
> > > > >> that rely on code patching.  
> > > > >
> > > > > Since we can define extra RW sections to place some tiny code bits in
> > > > > RAM, I would suggest that you hold back this patch for a while.
> > > > > I am not going to support the idea of e. g. compiling KGDB support
> > > > > into a XIP kernel, but disabling the whole HAVE_ARCH_JUMP_LABEL is
> > > > > hardly the way to go.  
> > > >
> > > > Do you have any updates on this?  The SOC_SIFIVE disable thread floated
> > > > back to the top of my inbox and I didn't see anything there.  I'd prefer
> > > > to avoid chasing around Kconfig disables for a bunch of stuff that we're
> > > > just going to fix soon, but if this is going to be a big change then
> > > > it's likely for next cycle anyway so in that case I'll start picking up
> > > > these compile disable patches.  
> > >
> > > Sorry, was caught up in fixing other stuff but now I'm on it so expect
> > > some updates soon.  
> >
> > Hi Vitaly,
> >
> > Based on your "[PATCH] riscv: xip: support runtime trap patching", IMHO, it
> > solves ERRATA patching issue(And it makes use of the fact that the ERRATA
> > only touches traps at the moment), but can't make code patching tech such as
> > KPROBES, DYNAMIC_FTRACE etc. work properly, so my patch is still needed.  
> 
> At this point it is needed, yes.
> 
> The thing is, I thought I'd go with one problem at a time, so I posted
> the patch which solves build issues for SOC_SIFIVE and XIP, and
> runtime patching for ERRATA (and I hope it gets accepted and makes its
> way into -stable, too).
> I gathered that addressing your issue had lower priority and so it's

It's at lower priority, in fact I didn't have XIP riscv platform ;)

> still underway. All in all, I don't mind going on with your patch,
> when the initial issue is addressed, we may want to revert some part
> of it but I guess that would be ok with you, wouldn't it?

We could revert some part of it later although I suspect the incompatibility
between code patching tech and XIP could be addressed, take the KPROBES
for example, it needs an ability to patch almost *every* can_be_kprobed insn
this isn't achievable/necessary in XIP case.

Thanks

> 
> Best regards,
>    Vitaly
> 
> > What do you think?
> >
> > Regards
> >  
> > >
> > > Best regards,
> > >    Vitaly
> > >  
> > > > Not trying to rush any thing here, just don't want to have a bunch of
> > > > broken configs.
> > > >  
> > > > >
> > > > > Best regards,
> > > > >    Vitaly
> > > > >  
> > > > >> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> > > > >> ---
> > > > >> Hi,
> > > > >>
> > > > >> Currently, the RISCV_ERRATA_ALTERNATIVE also only works on !XIP_KERNEL
> > > > >> but from the maillist it seem there's effort to make the co-exist, so
> > > > >> I drop RISCV_ERRATA_ALTERNATIVE dependency on !XIP_KERNEL.
> > > > >>
> > > > >> Thanks
> > > > >>
> > > > >>  arch/riscv/Kconfig | 18 +++++++++---------
> > > > >>  1 file changed, 9 insertions(+), 9 deletions(-)
> > > > >>
> > > > >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > >> index a8ad8eb76120..61320b94ef97 100644
> > > > >> --- a/arch/riscv/Kconfig
> > > > >> +++ b/arch/riscv/Kconfig
> > > > >> @@ -60,11 +60,11 @@ config RISCV
> > > > >>         select GENERIC_TIME_VSYSCALL if MMU && 64BIT
> > > > >>         select HANDLE_DOMAIN_IRQ
> > > > >>         select HAVE_ARCH_AUDITSYSCALL
> > > > >> -       select HAVE_ARCH_JUMP_LABEL
> > > > >> -       select HAVE_ARCH_JUMP_LABEL_RELATIVE
> > > > >> +       select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
> > > > >> +       select HAVE_ARCH_JUMP_LABEL_RELATIVE if !XIP_KERNEL
> > > > >>         select HAVE_ARCH_KASAN if MMU && 64BIT
> > > > >>         select HAVE_ARCH_KASAN_VMALLOC if MMU && 64BIT
> > > > >> -       select HAVE_ARCH_KGDB
> > > > >> +       select HAVE_ARCH_KGDB if !XIP_KERNEL
> > > > >>         select HAVE_ARCH_KGDB_QXFER_PKT
> > > > >>         select HAVE_ARCH_MMAP_RND_BITS if MMU
> > > > >>         select HAVE_ARCH_SECCOMP_FILTER
> > > > >> @@ -79,9 +79,9 @@ config RISCV
> > > > >>         select HAVE_GCC_PLUGINS
> > > > >>         select HAVE_GENERIC_VDSO if MMU && 64BIT
> > > > >>         select HAVE_IRQ_TIME_ACCOUNTING
> > > > >> -       select HAVE_KPROBES
> > > > >> -       select HAVE_KPROBES_ON_FTRACE
> > > > >> -       select HAVE_KRETPROBES
> > > > >> +       select HAVE_KPROBES if !XIP_KERNEL
> > > > >> +       select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
> > > > >> +       select HAVE_KRETPROBES if !XIP_KERNEL
> > > > >>         select HAVE_PCI
> > > > >>         select HAVE_PERF_EVENTS
> > > > >>         select HAVE_PERF_REGS
> > > > >> @@ -230,11 +230,11 @@ config ARCH_RV64I
> > > > >>         bool "RV64I"
> > > > >>         select 64BIT
> > > > >>         select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && GCC_VERSION >= 50000
> > > > >> -       select HAVE_DYNAMIC_FTRACE if MMU && $(cc-option,-fpatchable-function-entry=8)
> > > > >> +       select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
> > > > >>         select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> > > > >> -       select HAVE_FTRACE_MCOUNT_RECORD
> > > > >> +       select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> > > > >>         select HAVE_FUNCTION_GRAPH_TRACER
> > > > >> -       select HAVE_FUNCTION_TRACER
> > > > >> +       select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> > > > >>         select SWIOTLB if MMU
> > > > >>
> > > > >>  endchoice
> > > > >> --
> > > > >> 2.31.0
> > > > >>
> > > > >>
> > > > >>
> > > > >> _______________________________________________