From: Masami Hiramatsu <mhiramat@kernel.org>
To: Zong Li <zong.li@sifive.com>
Cc: linux-riscv <linux-riscv@lists.infradead.org>,
Albert Ou <aou@eecs.berkeley.edu>,
Palmer Dabbelt <palmer@dabbelt.com>,
"linux-kernel@vger.kernel.org List"
<linux-kernel@vger.kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>
Subject: Re: [PATCH v3 8/9] riscv: introduce interfaces to patch kernel code
Date: Sat, 4 Apr 2020 12:14:28 +0900 [thread overview]
Message-ID: <20200404121428.596911ba5653f8b18a80eab2@kernel.org> (raw)
In-Reply-To: <CANXhq0rMbkNxQ3_qqYEKe8DSbL-vfQku6V9a81Hy9cxW4LaW9g@mail.gmail.com>
Hi Zong,
On Fri, 3 Apr 2020 17:04:51 +0800
Zong Li <zong.li@sifive.com> wrote:
> > > > > +{
> > > > > + void *waddr = addr;
> > > > > + bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
> > > > > + unsigned long flags = 0;
> > > > > + int ret;
> > > > > +
> > > > > + raw_spin_lock_irqsave(&patch_lock, flags);
> > > >
> > > > This looks a bit odd since stop_machine() is protected by its own mutex,
> > > > and also the irq is already disabled here.
> > >
> > > We need it because we don't always enter the riscv_patch_text_nosync()
> > > through stop_machine mechanism. If we call the
> > > riscv_patch_text_nosync() directly, we need a lock to protect the
> > > page.
> >
> > Oh, OK, but it leads another question. Is that safe to patch the
> > text without sync? Would you use it for UP system?
> > I think it is better to clarify "in what case user can call _nosync()"
> > and add a comment on it.
>
> The ftrace is one of the cases, as documentation of ftrace said, when
> dynamic ftrace is initialized, it calls kstop_machine to make the
> machine act like a uniprocessor so that it can freely modify code
> without worrying about other processors executing that same code. So
> the ftrace called the _nosync interface here directly.
Hmm, even though, since it already running under kstop_machine(), no
other thread will run.
Could you consider to use text_mutex instead of that? The text_mutex
is already widely used in x86 and kernel/kprobes.c etc.
(Hmm, it seems except for x86, alternative code don't care about
racing...)
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-04-04 3:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 16:55 [PATCH v3 0/9] Support strict kernel memory permissions for security Zong Li
2020-03-09 16:55 ` [PATCH v3 1/9] riscv: add ARCH_HAS_SET_MEMORY support Zong Li
2020-03-09 16:55 ` [PATCH v3 2/9] riscv: add ARCH_HAS_SET_DIRECT_MAP support Zong Li
2020-03-09 16:55 ` [PATCH v3 3/9] riscv: add ARCH_SUPPORTS_DEBUG_PAGEALLOC support Zong Li
2020-03-09 16:55 ` [PATCH v3 4/9] riscv: move exception table immediately after RO_DATA Zong Li
2020-03-09 16:55 ` [PATCH v3 5/9] riscv: add alignment for text, rodata and data sections Zong Li
2020-03-09 16:55 ` [PATCH v3 6/9] riscv: add STRICT_KERNEL_RWX support Zong Li
2020-03-09 16:55 ` [PATCH v3 7/9] riscv: add macro to get instruction length Zong Li
2020-03-09 16:55 ` [PATCH v3 8/9] riscv: introduce interfaces to patch kernel code Zong Li
2020-03-31 15:32 ` Masami Hiramatsu
2020-04-01 7:42 ` Zong Li
2020-04-02 1:17 ` Masami Hiramatsu
2020-04-03 9:04 ` Zong Li
2020-04-04 3:14 ` Masami Hiramatsu [this message]
2020-04-04 12:12 ` Zong Li
2020-04-06 10:36 ` Zong Li
2020-04-07 12:29 ` Masami Hiramatsu
2020-04-07 13:06 ` Zong Li
2020-03-09 16:55 ` [PATCH v3 9/9] riscv: patch code by fixmap mapping Zong Li
2020-03-31 13:32 ` [PATCH v3 0/9] Support strict kernel memory permissions for security Masami Hiramatsu
2020-04-01 7:18 ` Zong Li
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