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 <[email protected]>
---
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
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 <[email protected]>
> ---
> 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 <[email protected]>
--
Damien Le Moal
Western Digital
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 <[email protected]>
>> ---
>> 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 <[email protected]>
>
> --
> Damien Le Moal
> Western Digital
On Sat, 26 Sep 2020 22:35:39 PDT (-0700), [email protected] wrote:
> On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <[email protected]> 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 <[email protected]>
>> >> ---
>> >> 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 <[email protected]>
>> >
>> > --
>> > Damien Le Moal
>> > Western Digital
On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <[email protected]> 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 <[email protected]>
> >> ---
> >> 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 <[email protected]>
> >
> > --
> > Damien Le Moal
> > Western Digital
On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <[email protected]> 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 <[email protected]>
> >> ---
> >> 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 <[email protected]>
> >
> > --
> > Damien Le Moal
> > Western Digital
On Sat, 26 Sep 2020 22:38:17 PDT (-0700), [email protected] wrote:
> On Sun, Sep 27, 2020 at 5:50 AM Palmer Dabbelt <[email protected]> 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 <[email protected]>
>> >> ---
>> >> 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 <[email protected]>
>> >
>> > --
>> > Damien Le Moal
>> > Western Digital