On Thu, Oct 29, 2020 at 08:26:26PM +0530, Sumit Garg wrote:
> Add a new API kgdb_arch_roundup_cpus() for a particular archichecture to
> override default kgdb roundup and if it detects at runtime to not support
> NMI roundup then it can fallback to default implementation using async
> SMP cross-calls.
>
> Currently such an architecture example is arm64 supporting pseudo NMIs
> feature which is only available on platforms which have support for GICv3
> or later version.
>
> Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
> ---
> arch/powerpc/kernel/kgdb.c | 3 ++-
> arch/sparc/kernel/smp_64.c | 3 ++-
> arch/x86/kernel/kgdb.c | 6 ++++--
> include/linux/kgdb.h | 5 +++--
> kernel/debug/debug_core.c | 10 +++++++++-
> 5 files changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index 4090802..126575d 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -125,9 +125,10 @@ static int kgdb_debugger_ipi(struct pt_regs *regs)
> }
>
> #ifdef CONFIG_SMP
> -void kgdb_roundup_cpus(void)
> +bool kgdb_arch_roundup_cpus(void)
> {
> smp_send_debugger_break();
> + return true;
> }
> #endif
>
> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
> index e38d8bf..c459c83 100644
> --- a/arch/sparc/kernel/smp_64.c
> +++ b/arch/sparc/kernel/smp_64.c
> @@ -1014,9 +1014,10 @@ void flush_dcache_page_all(struct mm_struct *mm,
> struct page *page)
> }
>
> #ifdef CONFIG_KGDB
> -void kgdb_roundup_cpus(void)
> +bool kgdb_arch_roundup_cpus(void)
> {
> smp_cross_call(&xcall_kgdb_capture, 0, 0, 0);
> + return true;
> }
> #endif
>
> diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
> index ff7878d..1b756d9 100644
> --- a/arch/x86/kernel/kgdb.c
> +++ b/arch/x86/kernel/kgdb.c
> @@ -404,7 +404,8 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs)
>
> #ifdef CONFIG_SMP
> /**
> - * kgdb_roundup_cpus - Get other CPUs into a holding pattern
> + * kgdb_arch_roundup_cpus - Get other CPUs into a holding pattern
> + * in an architectural specific manner
> *
> * On SMP systems, we need to get the attention of the other CPUs
> * and get them be in a known state. This should do what is needed
> @@ -414,9 +415,10 @@ static void kgdb_disable_hw_debug(struct pt_regs *regs)
> *
> * On non-SMP systems, this is not called.
> */
> -void kgdb_roundup_cpus(void)
> +bool kgdb_arch_roundup_cpus(void)
> {
> apic_send_IPI_allbutself(NMI_VECTOR);
> + return true;
> }
> #endif
>
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index 0d6cf64..f9db5b8 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -200,7 +200,8 @@ kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,
> extern void kgdb_call_nmi_hook(void *ignored);
>
> /**
> - * kgdb_roundup_cpus - Get other CPUs into a holding pattern
> + * kgdb_arch_roundup_cpus - Get other CPUs into a holding pattern
> + * in an architectural specific manner
> *
> * On SMP systems, we need to get the attention of the other CPUs
> * and get them into a known state. This should do what is needed
> @@ -210,7 +211,7 @@ extern void kgdb_call_nmi_hook(void *ignored);
> *
> * On non-SMP systems, this is not called.
> */
> -extern void kgdb_roundup_cpus(void);
> +extern bool kgdb_arch_roundup_cpus(void);
>
> /**
> * kgdb_arch_set_pc - Generic call back to the program counter
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 1e75a89..27e401c 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -241,13 +241,21 @@ void __weak kgdb_call_nmi_hook(void *ignored)
> }
> NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
>
> -void __weak kgdb_roundup_cpus(void)
> +bool __weak kgdb_arch_roundup_cpus(void)
> +{
> + return false;
Do we really need to introduce all these boolean return values just to
call a bit of library code when one of the architectures wants to
fallback to a generic implementation?
Why not something more like:
void kgdb_smp_call_nmi_hook(void)
{
/* original weak version of kgdb_roundup_cpus goes here */
}
void __weak kgdb_roundup_cpus(void)
{
kgdb_smp_call_nmi_hook();
}
arm64 can now simply call the new library function if a fallback is needed.
Note that same question applies to the backtrace changes...
Daniel.
> +}
> +
> +static void kgdb_roundup_cpus(void)
> {
> call_single_data_t *csd;
> int this_cpu = raw_smp_processor_id();
> int cpu;
> int ret;
>
> + if (kgdb_arch_roundup_cpus())
> + return;
> +
> for_each_online_cpu(cpu) {
> /* No need to roundup ourselves */
> if (cpu == this_cpu)
> --
> 2.7.4
>
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