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* [PATCH v2] RISC-V: Check clint_time_val before use
@ 2020-09-26 10:21 Anup Patel
  2020-09-26 10:31 ` Damien Le Moal
  0 siblings, 1 reply; 7+ messages in thread
From: Anup Patel @ 2020-09-26 10:21 UTC (permalink / raw)
  To: Palmer Dabbelt, Palmer Dabbelt, Paul Walmsley, Albert Ou
  Cc: Atish Patra, Alistair Francis, Damien Le Moal, Anup Patel,
	linux-riscv, linux-kernel, Anup Patel

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@wdc.com>
---
Changes since v1:
 - Explicitly initialize clint_time_val to NULL in CLINT driver to
   avoid hang on Kendryte K210
---
 arch/riscv/include/asm/timex.h    | 12 +++++++++---
 drivers/clocksource/timer-clint.c |  2 +-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 7f659dda0032..6e7b04874755 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 */
diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index d17367dee02c..8dbec85979fd 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
 static unsigned int clint_timer_irq;
 
 #ifdef CONFIG_RISCV_M_MODE
-u64 __iomem *clint_time_val;
+u64 __iomem *clint_time_val = NULL;
 #endif
 
 static void clint_send_ipi(const struct cpumask *target)
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-26 10:21 [PATCH v2] RISC-V: Check clint_time_val before use Anup Patel
@ 2020-09-26 10:31 ` Damien Le Moal
  2020-09-27  0:20   ` Palmer Dabbelt
  0 siblings, 1 reply; 7+ messages in thread
From: Damien Le Moal @ 2020-09-26 10:31 UTC (permalink / raw)
  To: paul.walmsley, palmer, palmerdabbelt, Anup Patel, aou
  Cc: anup, linux-riscv, Atish Patra, Alistair Francis, linux-kernel

On Sat, 2020-09-26 at 15:51 +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@wdc.com>
> ---
> Changes since v1:
>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>    avoid hang on Kendryte K210
> ---
>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
>  drivers/clocksource/timer-clint.c |  2 +-
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..6e7b04874755 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 */
> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> index d17367dee02c..8dbec85979fd 100644
> --- a/drivers/clocksource/timer-clint.c
> +++ b/drivers/clocksource/timer-clint.c
> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
>  static unsigned int clint_timer_irq;
>  
>  #ifdef CONFIG_RISCV_M_MODE
> -u64 __iomem *clint_time_val;
> +u64 __iomem *clint_time_val = NULL;
>  #endif
>  
>  static void clint_send_ipi(const struct cpumask *target)

For Kendryte:

Tested-by: Damien Le Moal <damien.lemoal@wdc.com>

-- 
Damien Le Moal
Western Digital

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-26 10:31 ` Damien Le Moal
@ 2020-09-27  0:20   ` Palmer Dabbelt
  2020-09-27  5:35     ` Anup Patel
  2020-09-27  5:38     ` Anup Patel
  0 siblings, 2 replies; 7+ messages in thread
From: Palmer Dabbelt @ 2020-09-27  0:20 UTC (permalink / raw)
  To: Damien Le Moal
  Cc: Paul Walmsley, Anup Patel, aou, anup, linux-riscv, Atish Patra,
	Alistair Francis, linux-kernel

On Sat, 26 Sep 2020 03:31:29 PDT (-0700), Damien Le Moal wrote:
> On Sat, 2020-09-26 at 15:51 +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.

I don't think this is the right way to solve that problem, as we're essentially
just lying about the timer rather than informing the system we can't get
timer-based entropy right now.  MIPS is explicit about this, I don't see any
reason why we shouldn't be as well.

Does this fix the boot issue (see below for the NULL)?  There's some other
random-related arch functions so this might not be quite the right way to do
it.

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 7f659dda0032..7e39b0068932 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -33,6 +33,18 @@ static inline u32 get_cycles_hi(void)
 #define get_cycles_hi get_cycles_hi
 #endif /* CONFIG_64BIT */
 
+/*
+ * Much like MIPS, we may not have a viable counter to use at an early point in
+ * the boot process.  Unfortunately we don't have a fallback, so instead we
+ * just return 0.
+ */
+static inline unsigned long random_get_entropy(void)
+{
+	if (unlikely(clint_time_val == NULL))
+		return 0;
+	return get_cycles();
+}
+
 #else /* CONFIG_RISCV_M_MODE */
 
 static inline cycles_t get_cycles(void)

>> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
>> for M-mode systems")
>> Signed-off-by: Anup Patel <anup.patel@wdc.com>
>> ---
>> Changes since v1:
>>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>>    avoid hang on Kendryte K210
>> ---
>>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
>>  drivers/clocksource/timer-clint.c |  2 +-
>>  2 files changed, 10 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> index 7f659dda0032..6e7b04874755 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 */
>> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
>> index d17367dee02c..8dbec85979fd 100644
>> --- a/drivers/clocksource/timer-clint.c
>> +++ b/drivers/clocksource/timer-clint.c
>> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
>>  static unsigned int clint_timer_irq;
>>  
>>  #ifdef CONFIG_RISCV_M_MODE
>> -u64 __iomem *clint_time_val;
>> +u64 __iomem *clint_time_val = NULL;

This one I definately don't get.  According the internet, the C standard says

    If an object that has static storage duration is not initialized
    explicitly, it is initialized implicitly as if every member that has
    arithmetic type were assigned 0 and every member that has pointer type were
    assigned a null pointer constant.

so unless I'm missing something there shouldn't be any difference between these
two lines.  When I just apply this I get exactly the same "objdump -dt" before
and after.  I do see some difference in assembly, but only when I don't pass
"-fno-common" and that ends up being passed during my Linux builds.

>>  #endif
>>  
>>  static void clint_send_ipi(const struct cpumask *target)
> 
> For Kendryte:
> 
> Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
> 
> -- 
> Damien Le Moal
> Western Digital

^ permalink raw reply related	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-27  0:20   ` Palmer Dabbelt
@ 2020-09-27  5:35     ` Anup Patel
  2020-09-27  5:37       ` Palmer Dabbelt
  2020-09-27  5:38     ` Anup Patel
  1 sibling, 1 reply; 7+ messages in thread
From: Anup Patel @ 2020-09-27  5:35 UTC (permalink / raw)
  To: Palmer Dabbelt
  Cc: Damien Le Moal, Paul Walmsley, Anup Patel, Albert Ou,
	linux-riscv, Atish Patra, Alistair Francis,
	linux-kernel@vger.kernel.org List

On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>
> On Sat, 26 Sep 2020 03:31:29 PDT (-0700), Damien Le Moal wrote:
> > On Sat, 2020-09-26 at 15:51 +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.
>
> I don't think this is the right way to solve that problem, as we're essentially
> just lying about the timer rather than informing the system we can't get
> timer-based entropy right now.  MIPS is explicit about this, I don't see any
> reason why we shouldn't be as well.
>
> Does this fix the boot issue (see below for the NULL)?  There's some other
> random-related arch functions so this might not be quite the right way to do
> it.
>
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..7e39b0068932 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -33,6 +33,18 @@ static inline u32 get_cycles_hi(void)
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */
>
> +/*
> + * Much like MIPS, we may not have a viable counter to use at an early point in
> + * the boot process.  Unfortunately we don't have a fallback, so instead we
> + * just return 0.
> + */
> +static inline unsigned long random_get_entropy(void)
> +{
> +       if (unlikely(clint_time_val == NULL))
> +               return 0;
> +       return get_cycles();
> +}
> +

Overall, this approach is good but this change is incomplete so does not work.

The linux/timex.h expects random_get_entropy() to be macro so we need a
"#define" as well.

After fixing rand_initialize() with custom random_get_entropy(), we get another
issue in boot_init_stack_canary() because boot_init_stack_canary() directly
calls get_cycles() so we remove use of get_cycles() from
boot_init_stack_canary()
and this is similar to ARM, ARM64, and MIPS kernel.

Regards,
Anup

>  #else /* CONFIG_RISCV_M_MODE */
>
>  static inline cycles_t get_cycles(void)
>
> >> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> >> for M-mode systems")
> >> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> >> ---
> >> Changes since v1:
> >>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
> >>    avoid hang on Kendryte K210
> >> ---
> >>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
> >>  drivers/clocksource/timer-clint.c |  2 +-
> >>  2 files changed, 10 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> >> index 7f659dda0032..6e7b04874755 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 */
> >> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> >> index d17367dee02c..8dbec85979fd 100644
> >> --- a/drivers/clocksource/timer-clint.c
> >> +++ b/drivers/clocksource/timer-clint.c
> >> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
> >>  static unsigned int clint_timer_irq;
> >>
> >>  #ifdef CONFIG_RISCV_M_MODE
> >> -u64 __iomem *clint_time_val;
> >> +u64 __iomem *clint_time_val = NULL;
>
> This one I definately don't get.  According the internet, the C standard says
>
>     If an object that has static storage duration is not initialized
>     explicitly, it is initialized implicitly as if every member that has
>     arithmetic type were assigned 0 and every member that has pointer type were
>     assigned a null pointer constant.
>
> so unless I'm missing something there shouldn't be any difference between these
> two lines.  When I just apply this I get exactly the same "objdump -dt" before
> and after.  I do see some difference in assembly, but only when I don't pass
> "-fno-common" and that ends up being passed during my Linux builds.
>
> >>  #endif
> >>
> >>  static void clint_send_ipi(const struct cpumask *target)
> >
> > For Kendryte:
> >
> > Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
> >
> > --
> > Damien Le Moal
> > Western Digital

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-27  5:35     ` Anup Patel
@ 2020-09-27  5:37       ` Palmer Dabbelt
  0 siblings, 0 replies; 7+ messages in thread
From: Palmer Dabbelt @ 2020-09-27  5:37 UTC (permalink / raw)
  To: anup
  Cc: Damien Le Moal, Paul Walmsley, Anup Patel, aou, linux-riscv,
	Atish Patra, Alistair Francis, linux-kernel

On Sat, 26 Sep 2020 22:35:39 PDT (-0700), anup@brainfault.org wrote:
> On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>>
>> On Sat, 26 Sep 2020 03:31:29 PDT (-0700), Damien Le Moal wrote:
>> > On Sat, 2020-09-26 at 15:51 +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.
>>
>> I don't think this is the right way to solve that problem, as we're essentially
>> just lying about the timer rather than informing the system we can't get
>> timer-based entropy right now.  MIPS is explicit about this, I don't see any
>> reason why we shouldn't be as well.
>>
>> Does this fix the boot issue (see below for the NULL)?  There's some other
>> random-related arch functions so this might not be quite the right way to do
>> it.
>>
>> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> index 7f659dda0032..7e39b0068932 100644
>> --- a/arch/riscv/include/asm/timex.h
>> +++ b/arch/riscv/include/asm/timex.h
>> @@ -33,6 +33,18 @@ static inline u32 get_cycles_hi(void)
>>  #define get_cycles_hi get_cycles_hi
>>  #endif /* CONFIG_64BIT */
>>
>> +/*
>> + * Much like MIPS, we may not have a viable counter to use at an early point in
>> + * the boot process.  Unfortunately we don't have a fallback, so instead we
>> + * just return 0.
>> + */
>> +static inline unsigned long random_get_entropy(void)
>> +{
>> +       if (unlikely(clint_time_val == NULL))
>> +               return 0;
>> +       return get_cycles();
>> +}
>> +
>
> Overall, this approach is good but this change is incomplete so does not work.
>
> The linux/timex.h expects random_get_entropy() to be macro so we need a
> "#define" as well.
>
> After fixing rand_initialize() with custom random_get_entropy(), we get another
> issue in boot_init_stack_canary() because boot_init_stack_canary() directly
> calls get_cycles() so we remove use of get_cycles() from
> boot_init_stack_canary()
> and this is similar to ARM, ARM64, and MIPS kernel.

OK, are you going to send that patch or do you want me to?

>
> Regards,
> Anup
>
>>  #else /* CONFIG_RISCV_M_MODE */
>>
>>  static inline cycles_t get_cycles(void)
>>
>> >> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
>> >> for M-mode systems")
>> >> Signed-off-by: Anup Patel <anup.patel@wdc.com>
>> >> ---
>> >> Changes since v1:
>> >>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>> >>    avoid hang on Kendryte K210
>> >> ---
>> >>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
>> >>  drivers/clocksource/timer-clint.c |  2 +-
>> >>  2 files changed, 10 insertions(+), 4 deletions(-)
>> >>
>> >> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> >> index 7f659dda0032..6e7b04874755 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 */
>> >> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
>> >> index d17367dee02c..8dbec85979fd 100644
>> >> --- a/drivers/clocksource/timer-clint.c
>> >> +++ b/drivers/clocksource/timer-clint.c
>> >> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
>> >>  static unsigned int clint_timer_irq;
>> >>
>> >>  #ifdef CONFIG_RISCV_M_MODE
>> >> -u64 __iomem *clint_time_val;
>> >> +u64 __iomem *clint_time_val = NULL;
>>
>> This one I definately don't get.  According the internet, the C standard says
>>
>>     If an object that has static storage duration is not initialized
>>     explicitly, it is initialized implicitly as if every member that has
>>     arithmetic type were assigned 0 and every member that has pointer type were
>>     assigned a null pointer constant.
>>
>> so unless I'm missing something there shouldn't be any difference between these
>> two lines.  When I just apply this I get exactly the same "objdump -dt" before
>> and after.  I do see some difference in assembly, but only when I don't pass
>> "-fno-common" and that ends up being passed during my Linux builds.
>>
>> >>  #endif
>> >>
>> >>  static void clint_send_ipi(const struct cpumask *target)
>> >
>> > For Kendryte:
>> >
>> > Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
>> >
>> > --
>> > Damien Le Moal
>> > Western Digital

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-27  0:20   ` Palmer Dabbelt
  2020-09-27  5:35     ` Anup Patel
@ 2020-09-27  5:38     ` Anup Patel
  2020-09-27  5:39       ` Palmer Dabbelt
  1 sibling, 1 reply; 7+ messages in thread
From: Anup Patel @ 2020-09-27  5:38 UTC (permalink / raw)
  To: Palmer Dabbelt
  Cc: Damien Le Moal, Paul Walmsley, Anup Patel, Albert Ou,
	linux-riscv, Atish Patra, Alistair Francis,
	linux-kernel@vger.kernel.org List

On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>
> On Sat, 26 Sep 2020 03:31:29 PDT (-0700), Damien Le Moal wrote:
> > On Sat, 2020-09-26 at 15:51 +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.
>
> I don't think this is the right way to solve that problem, as we're essentially
> just lying about the timer rather than informing the system we can't get
> timer-based entropy right now.  MIPS is explicit about this, I don't see any
> reason why we shouldn't be as well.
>
> Does this fix the boot issue (see below for the NULL)?  There's some other
> random-related arch functions so this might not be quite the right way to do
> it.
>
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..7e39b0068932 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -33,6 +33,18 @@ static inline u32 get_cycles_hi(void)
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */
>
> +/*
> + * Much like MIPS, we may not have a viable counter to use at an early point in
> + * the boot process.  Unfortunately we don't have a fallback, so instead we
> + * just return 0.
> + */
> +static inline unsigned long random_get_entropy(void)
> +{
> +       if (unlikely(clint_time_val == NULL))
> +               return 0;
> +       return get_cycles();
> +}
> +
>  #else /* CONFIG_RISCV_M_MODE */
>
>  static inline cycles_t get_cycles(void)
>
> >> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> >> for M-mode systems")
> >> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> >> ---
> >> Changes since v1:
> >>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
> >>    avoid hang on Kendryte K210
> >> ---
> >>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
> >>  drivers/clocksource/timer-clint.c |  2 +-
> >>  2 files changed, 10 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> >> index 7f659dda0032..6e7b04874755 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 */
> >> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> >> index d17367dee02c..8dbec85979fd 100644
> >> --- a/drivers/clocksource/timer-clint.c
> >> +++ b/drivers/clocksource/timer-clint.c
> >> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
> >>  static unsigned int clint_timer_irq;
> >>
> >>  #ifdef CONFIG_RISCV_M_MODE
> >> -u64 __iomem *clint_time_val;
> >> +u64 __iomem *clint_time_val = NULL;
>
> This one I definately don't get.  According the internet, the C standard says
>
>     If an object that has static storage duration is not initialized
>     explicitly, it is initialized implicitly as if every member that has
>     arithmetic type were assigned 0 and every member that has pointer type were
>     assigned a null pointer constant.
>
> so unless I'm missing something there shouldn't be any difference between these
> two lines.  When I just apply this I get exactly the same "objdump -dt" before
> and after.  I do see some difference in assembly, but only when I don't pass
> "-fno-common" and that ends up being passed during my Linux builds.

Even checkpatch complains about explicit NULL assignment to global variables.

I will send v3 with a different approach to fix this so hopefully with
v3 we will
not require explicit NULL assignment.

Regards,
Anup

>
> >>  #endif
> >>
> >>  static void clint_send_ipi(const struct cpumask *target)
> >
> > For Kendryte:
> >
> > Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
> >
> > --
> > Damien Le Moal
> > Western Digital

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] RISC-V: Check clint_time_val before use
  2020-09-27  5:38     ` Anup Patel
@ 2020-09-27  5:39       ` Palmer Dabbelt
  0 siblings, 0 replies; 7+ messages in thread
From: Palmer Dabbelt @ 2020-09-27  5:39 UTC (permalink / raw)
  To: anup
  Cc: Damien Le Moal, Paul Walmsley, Anup Patel, aou, linux-riscv,
	Atish Patra, Alistair Francis, linux-kernel

On Sat, 26 Sep 2020 22:38:17 PDT (-0700), anup@brainfault.org wrote:
> On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>>
>> On Sat, 26 Sep 2020 03:31:29 PDT (-0700), Damien Le Moal wrote:
>> > On Sat, 2020-09-26 at 15:51 +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.
>>
>> I don't think this is the right way to solve that problem, as we're essentially
>> just lying about the timer rather than informing the system we can't get
>> timer-based entropy right now.  MIPS is explicit about this, I don't see any
>> reason why we shouldn't be as well.
>>
>> Does this fix the boot issue (see below for the NULL)?  There's some other
>> random-related arch functions so this might not be quite the right way to do
>> it.
>>
>> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> index 7f659dda0032..7e39b0068932 100644
>> --- a/arch/riscv/include/asm/timex.h
>> +++ b/arch/riscv/include/asm/timex.h
>> @@ -33,6 +33,18 @@ static inline u32 get_cycles_hi(void)
>>  #define get_cycles_hi get_cycles_hi
>>  #endif /* CONFIG_64BIT */
>>
>> +/*
>> + * Much like MIPS, we may not have a viable counter to use at an early point in
>> + * the boot process.  Unfortunately we don't have a fallback, so instead we
>> + * just return 0.
>> + */
>> +static inline unsigned long random_get_entropy(void)
>> +{
>> +       if (unlikely(clint_time_val == NULL))
>> +               return 0;
>> +       return get_cycles();
>> +}
>> +
>>  #else /* CONFIG_RISCV_M_MODE */
>>
>>  static inline cycles_t get_cycles(void)
>>
>> >> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
>> >> for M-mode systems")
>> >> Signed-off-by: Anup Patel <anup.patel@wdc.com>
>> >> ---
>> >> Changes since v1:
>> >>  - Explicitly initialize clint_time_val to NULL in CLINT driver to
>> >>    avoid hang on Kendryte K210
>> >> ---
>> >>  arch/riscv/include/asm/timex.h    | 12 +++++++++---
>> >>  drivers/clocksource/timer-clint.c |  2 +-
>> >>  2 files changed, 10 insertions(+), 4 deletions(-)
>> >>
>> >> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
>> >> index 7f659dda0032..6e7b04874755 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 */
>> >> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
>> >> index d17367dee02c..8dbec85979fd 100644
>> >> --- a/drivers/clocksource/timer-clint.c
>> >> +++ b/drivers/clocksource/timer-clint.c
>> >> @@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
>> >>  static unsigned int clint_timer_irq;
>> >>
>> >>  #ifdef CONFIG_RISCV_M_MODE
>> >> -u64 __iomem *clint_time_val;
>> >> +u64 __iomem *clint_time_val = NULL;
>>
>> This one I definately don't get.  According the internet, the C standard says
>>
>>     If an object that has static storage duration is not initialized
>>     explicitly, it is initialized implicitly as if every member that has
>>     arithmetic type were assigned 0 and every member that has pointer type were
>>     assigned a null pointer constant.
>>
>> so unless I'm missing something there shouldn't be any difference between these
>> two lines.  When I just apply this I get exactly the same "objdump -dt" before
>> and after.  I do see some difference in assembly, but only when I don't pass
>> "-fno-common" and that ends up being passed during my Linux builds.
>
> Even checkpatch complains about explicit NULL assignment to global variables.
>
> I will send v3 with a different approach to fix this so hopefully with
> v3 we will
> not require explicit NULL assignment.

Awesome, thanks!

>
> Regards,
> Anup
>
>>
>> >>  #endif
>> >>
>> >>  static void clint_send_ipi(const struct cpumask *target)
>> >
>> > For Kendryte:
>> >
>> > Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
>> >
>> > --
>> > Damien Le Moal
>> > Western Digital

^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-09-27  5:39 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-26 10:21 [PATCH v2] RISC-V: Check clint_time_val before use Anup Patel
2020-09-26 10:31 ` Damien Le Moal
2020-09-27  0:20   ` Palmer Dabbelt
2020-09-27  5:35     ` Anup Patel
2020-09-27  5:37       ` Palmer Dabbelt
2020-09-27  5:38     ` Anup Patel
2020-09-27  5:39       ` Palmer Dabbelt

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