On Thu, Nov 16, 2017 at 07:26:43PM -0200, Guilherme G. Piccoli wrote:
> On 11/06/2017 03:34 PM, Thadeu Lima de Souza Cascardo wrote:
> > From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
> >
> > The kernel boot parameter 'nr_cpus=' allows one to specify number of
> > possible cpus in the system. In the normal scenario the first cpu (cpu0)
> > that shows up is the boot cpu and hence it gets covered under nr_cpus
> > limit.
> >
> > But this assumption will be broken in kdump scenario where kdump kenrel
>
> Minor nit: s/kenrel/kernel
>
> > after a crash can boot up on an non-zero boot cpu. The paca structure
> > allocation depends on value of nr_cpus and is indexed using logical cpu
> > ids. This definetly will be an issue if boot cpu id > nr_cpus
>
> Minor nit (2): s/definetly/definitely
Hi, Guilherme.
Thanks a lot for testing and reviewing the patch. I will ignore those
small typos, unless the maintainers tell me to fix them. I hope you
don't mind.
I would like to see this merged sooner rather than later.
Thanks.
Cascardo.
> >
> > This patch modifies allocate_pacas() and smp_setup_cpu_maps() to
> > accommodate boot cpu for the case where boot_cpuid > nr_cpu_ids.
> >
> > This change would help to reduce the memory reservation requirement for
> > kdump on ppc64.
> >
> > Signed-off-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
> > Signed-off-by: Thadeu Lima de Souza Cascardo <casca...@canonical.com>
>
> Tested-by: Guilherme G. Piccoli <gpicc...@linux.vnet.ibm.com>
>
> Without this patch, got a crash deterministically when booting with
> nr_cpus=1 in P8 bare-metal. The patch fixes the issue...
>
> Thanks,
>
>
> Guilherme
>
>
> > ---
> >
> > v3: fixup signedness or nr_cpus to match nr_cpu_ids
> > and fix conflict due to change from %d to %u
> >
> > Resending this as it was not applied, and I can reproduce the issue with
> > v4.14-rc8 when booting a kdump kernel after a crash that has been given
> > nr_cpus=1 as a parameter. With this patch, I can't reproduce it anymore.
> >
> > ---
> > arch/powerpc/include/asm/paca.h | 3 +++
> > arch/powerpc/include/asm/smp.h | 1 +
> > arch/powerpc/kernel/paca.c | 23 +++++++++++++++++-----
> > arch/powerpc/kernel/prom.c | 39
> > +++++++++++++++++++++++++++++++++++++-
> > arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++++
> > 5 files changed, 85 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/paca.h
> > b/arch/powerpc/include/asm/paca.h
> > index 04b60af027ae..ea0dbf2bbeef 100644
> > --- a/arch/powerpc/include/asm/paca.h
> > +++ b/arch/powerpc/include/asm/paca.h
> > @@ -49,6 +49,9 @@ extern unsigned int debug_smp_processor_id(void); /* from
> > linux/smp.h */
> > #define get_lppaca() (get_paca()->lppaca_ptr)
> > #define get_slb_shadow() (get_paca()->slb_shadow_ptr)
> >
> > +/* Maximum number of threads per core. */
> > +#define MAX_SMT 8
> > +
> > struct task_struct;
> >
> > /*
> > diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> > index fac963e10d39..553cd22b2ccc 100644
> > --- a/arch/powerpc/include/asm/smp.h
> > +++ b/arch/powerpc/include/asm/smp.h
> > @@ -30,6 +30,7 @@
> > #include <asm/percpu.h>
> >
> > extern int boot_cpuid;
> > +extern int boot_hw_cpuid;
> > extern int spinning_secondaries;
> >
> > extern void cpu_die(void);
> > diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> > index 2ff2b8a19f71..9c689ee4b6a3 100644
> > --- a/arch/powerpc/kernel/paca.c
> > +++ b/arch/powerpc/kernel/paca.c
> > @@ -207,6 +207,7 @@ void __init allocate_pacas(void)
> > {
> > u64 limit;
> > int cpu;
> > + unsigned int nr_cpus;
> >
> > limit = ppc64_rma_size;
> >
> > @@ -219,20 +220,32 @@ void __init allocate_pacas(void)
> > limit = min(0x10000000ULL, limit);
> > #endif
> >
> > - paca_size = PAGE_ALIGN(sizeof(struct paca_struct) * nr_cpu_ids);
> > + /*
> > + * Always align up the nr_cpu_ids to SMT threads and allocate
> > + * the paca. This will help us to prepare for a situation where
> > + * boot cpu id > nr_cpus_id. We will use the last nthreads
> > + * slots (nthreads == threads per core) to accommodate a core
> > + * that contains boot cpu thread.
> > + *
> > + * Do not change nr_cpu_ids value here. Let us do that in
> > + * early_init_dt_scan_cpus() where we know exact value
> > + * of threads per core.
> > + */
> > + nr_cpus = _ALIGN_UP(nr_cpu_ids, MAX_SMT);
> > + paca_size = PAGE_ALIGN(sizeof(struct paca_struct) * nr_cpus);
> >
> > paca = __va(memblock_alloc_base(paca_size, PAGE_SIZE, limit));
> > memset(paca, 0, paca_size);
> >
> > printk(KERN_DEBUG "Allocated %u bytes for %u pacas at %p\n",
> > - paca_size, nr_cpu_ids, paca);
> > + paca_size, nr_cpus, paca);
> >
> > - allocate_lppacas(nr_cpu_ids, limit);
> > + allocate_lppacas(nr_cpus, limit);
> >
> > - allocate_slb_shadows(nr_cpu_ids, limit);
> > + allocate_slb_shadows(nr_cpus, limit);
> >
> > /* Can't use for_each_*_cpu, as they aren't functional yet */
> > - for (cpu = 0; cpu < nr_cpu_ids; cpu++)
> > + for (cpu = 0; cpu < nr_cpus; cpu++)
> > initialise_paca(&paca[cpu], cpu);
> > }
> >
> > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> > index f83056297441..93837093c5cb 100644
> > --- a/arch/powerpc/kernel/prom.c
> > +++ b/arch/powerpc/kernel/prom.c
> > @@ -302,6 +302,29 @@ static void __init
> > check_cpu_feature_properties(unsigned long node)
> > }
> > }
> >
> > +/*
> > + * Adjust the logical id of a boot cpu to fall under nr_cpu_ids. Map it to
> > + * last core slot in the allocated paca array.
> > + *
> > + * e.g. on SMT=8 system, kernel booted with nr_cpus=1 and boot cpu = 33,
> > + * align nr_cpu_ids to MAX_SMT value 8. Allocate paca array to hold up-to
> > + * MAX_SMT=8 cpus. Since boot cpu 33 is greater than nr_cpus (8), adjust
> > + * its logical id so that new id becomes less than nr_cpu_ids. Make sure
> > + * that boot cpu's new logical id is aligned to its thread id and falls
> > + * under last nthreads slots available in paca array. In this case the
> > + * boot cpu 33 is adjusted to new boot cpu id 1.
> > + *
> > + */
> > +static inline void adjust_boot_cpuid(int nthreads, int phys_id)
> > +{
> > + boot_hw_cpuid = phys_id;
> > + if (boot_cpuid >= nr_cpu_ids) {
> > + boot_cpuid = (boot_cpuid % nthreads) + (nr_cpu_ids - nthreads);
> > + pr_info("Adjusted logical boot cpu id: logical %d physical
> > %d\n",
> > + boot_cpuid, phys_id);
> > + }
> > +}
> > +
> > static int __init early_init_dt_scan_cpus(unsigned long node,
> > const char *uname, int depth,
> > void *data)
> > @@ -325,6 +348,18 @@ static int __init early_init_dt_scan_cpus(unsigned
> > long node,
> >
> > nthreads = len / sizeof(int);
> >
> > +#ifdef CONFIG_SMP
> > + /*
> > + * Now that we know threads per core lets align nr_cpu_ids to
> > + * correct SMT value.
> > + */
> > + if (nr_cpu_ids % nthreads) {
> > + nr_cpu_ids = _ALIGN_UP(nr_cpu_ids, nthreads);
> > + pr_info("Aligned nr_cpus to SMT=%d, nr_cpu_ids = %d\n",
> > + nthreads, nr_cpu_ids);
> > + }
> > +#endif
> > +
> > /*
> > * Now see if any of these threads match our boot cpu.
> > * NOTE: This must match the parsing done in smp_setup_cpu_maps.
> > @@ -363,7 +398,9 @@ static int __init early_init_dt_scan_cpus(unsigned long
> > node,
> > DBG("boot cpu: logical %d physical %d\n", found,
> > be32_to_cpu(intserv[found_thread]));
> > boot_cpuid = found;
> > - set_hard_smp_processor_id(found, be32_to_cpu(intserv[found_thread]));
> > + adjust_boot_cpuid(nthreads, be32_to_cpu(intserv[found_thread]));
> > + set_hard_smp_processor_id(boot_cpuid,
> > + be32_to_cpu(intserv[found_thread]));
> >
> > /*
> > * PAPR defines "logical" PVR values for cpus that
> > diff --git a/arch/powerpc/kernel/setup-common.c
> > b/arch/powerpc/kernel/setup-common.c
> > index 2e3bc16d02b2..46b1e0972a20 100644
> > --- a/arch/powerpc/kernel/setup-common.c
> > +++ b/arch/powerpc/kernel/setup-common.c
> > @@ -85,6 +85,7 @@ struct machdep_calls *machine_id;
> > EXPORT_SYMBOL(machine_id);
> >
> > int boot_cpuid = -1;
> > +int boot_hw_cpuid = -1;
> > EXPORT_SYMBOL_GPL(boot_cpuid);
> >
> > /*
> > @@ -473,6 +474,7 @@ void __init smp_setup_cpu_maps(void)
> > struct device_node *dn = NULL;
> > int cpu = 0;
> > int nthreads = 1;
> > + bool boot_cpu_added = false;
> >
> > DBG("smp_setup_cpu_maps()\n");
> >
> > @@ -499,6 +501,24 @@ void __init smp_setup_cpu_maps(void)
> > }
> >
> > nthreads = len / sizeof(int);
> > + /*
> > + * If boot cpu hasn't been added to paca and there are only
> > + * last nthreads slots available in paca array then wait
> > + * for boot cpu to show up.
> > + */
> > + if (!boot_cpu_added && (cpu + nthreads) >= nr_cpu_ids) {
> > + int found = 0;
> > +
> > + DBG("Holding last nthreads paca slots for boot cpu\n");
> > + for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> > + if (boot_hw_cpuid == be32_to_cpu(intserv[j])) {
> > + found = 1;
> > + break;
> > + }
> > + }
> > + if (!found)
> > + continue;
> > + }
> >
> > for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> > bool avail;
> > @@ -514,6 +534,11 @@ void __init smp_setup_cpu_maps(void)
> > set_cpu_present(cpu, avail);
> > set_hard_smp_processor_id(cpu, be32_to_cpu(intserv[j]));
> > set_cpu_possible(cpu, true);
> > + if (boot_hw_cpuid == be32_to_cpu(intserv[j])) {
> > + DBG("Boot cpu %d (hard id %d) added to paca\n",
> > + cpu, be32_to_cpu(intserv[j]));
> > + boot_cpu_added = true;
> > + }
> > cpu++;
> > }
> > }
> >
>
