linux-kernel - RE: [PATCH] RISC-V: Check clint_time

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Message-ID: <DM6PR04MB62017875C739101DF83280ED8D370@DM6PR04MB6201.namprd04.prod.outlook.com>
Date:   Sat, 26 Sep 2020 09:31:57 +0000
From:   Anup Patel <Anup.Patel@....com>
To:     Damien Le Moal <Damien.LeMoal@....com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "palmerdabbelt@...gle.com" <palmerdabbelt@...gle.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>
CC:     "anup@...infault.org" <anup@...infault.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] RISC-V: Check clint_time_val before use



> -----Original Message-----
> From: Damien Le Moal <Damien.LeMoal@....com>
> Sent: 26 September 2020 14:55
> To: paul.walmsley@...ive.com; palmer@...belt.com;
> palmerdabbelt@...gle.com; Anup Patel <Anup.Patel@....com>;
> aou@...s.berkeley.edu
> Cc: anup@...infault.org; linux-riscv@...ts.infradead.org; Atish Patra
> <Atish.Patra@....com>; Alistair Francis <Alistair.Francis@....com>; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH] RISC-V: Check clint_time_val before use
> 
> On Sat, 2020-09-26 at 12:57 +0530, Anup Patel wrote:
> > The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> > because the get_cycles() and friends are called very early from
> > rand_initialize() before CLINT driver is probed. To fix this, we
> > should check clint_time_val before use in get_cycles() and friends.
> >
> > Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> > for M-mode systems")
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > ---
> >  arch/riscv/include/asm/timex.h | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/timex.h
> > b/arch/riscv/include/asm/timex.h index 7f659dda0032..52b42bb1602c
> > 100644
> > --- a/arch/riscv/include/asm/timex.h
> > +++ b/arch/riscv/include/asm/timex.h
> > @@ -17,18 +17,24 @@ typedef unsigned long cycles_t;  #ifdef
> > CONFIG_64BIT  static inline cycles_t get_cycles(void)  {
> > -	return readq_relaxed(clint_time_val);
> > +	if (clint_time_val)
> > +		return readq_relaxed(clint_time_val);
> > +	return 0;
> >  }
> >  #else /* !CONFIG_64BIT */
> >  static inline u32 get_cycles(void)
> >  {
> > -	return readl_relaxed(((u32 *)clint_time_val));
> > +	if (clint_time_val)
> > +		return readl_relaxed(((u32 *)clint_time_val));
> > +	return 0;
> >  }
> >  #define get_cycles get_cycles
> >
> >  static inline u32 get_cycles_hi(void)  {
> > -	return readl_relaxed(((u32 *)clint_time_val) + 1);
> > +	if (clint_time_val)
> > +		return readl_relaxed(((u32 *)clint_time_val) + 1);
> > +	return 0
> >  }
> >  #define get_cycles_hi get_cycles_hi
> >  #endif /* CONFIG_64BIT */
> 
> Applying this on top of rc6, I now get a hang on Kendryte boot...
> No problems without the patch on the other hand.

Not sure about the issue with Kendryte but I get a crash on
QEMU virt machine without this patch.

Regards,
Anup