[PATCHv9 2/2] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt

Pingfan Liu piliu at redhat.com
Wed Nov 29 12:30:41 AEDT 2023


Hi Hari,


On Mon, Nov 27, 2023 at 12:30 PM Hari Bathini <hbathini at linux.ibm.com> wrote:
>
> Hi Pingfan, Michael,
>
> On 17/10/23 4:03 pm, Hari Bathini wrote:
> >
> >
> > On 17/10/23 7:58 am, Pingfan Liu wrote:
> >> *** Idea ***
> >> For kexec -p, the boot cpu can be not the cpu0, this causes the problem
> >> of allocating memory for paca_ptrs[]. However, in theory, there is no
> >> requirement to assign cpu's logical id as its present sequence in the
> >> device tree. But there is something like cpu_first_thread_sibling(),
> >> which makes assumption on the mapping inside a core. Hence partially
> >> loosening the mapping, i.e. unbind the mapping of core while keep the
> >> mapping inside a core.
> >>
> >> *** Implement ***
> >> At this early stage, there are plenty of memory to utilize. Hence, this
> >> patch allocates interim memory to link the cpu info on a list, then
> >> reorder cpus by changing the list head. As a result, there is a rotate
> >> shift between the sequence number in dt and the cpu logical number.
> >>
> >> *** Result ***
> >> After this patch, a boot-cpu's logical id will always be mapped into the
> >> range [0,threads_per_core).
> >>
> >> Besides this, at this phase, all threads in the boot core are forced to
> >> be onlined. This restriction will be lifted in a later patch with
> >> extra effort.
> >>
> >> Signed-off-by: Pingfan Liu <piliu at redhat.com>
> >> Cc: Michael Ellerman <mpe at ellerman.id.au>
> >> Cc: Nicholas Piggin <npiggin at gmail.com>
> >> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> >> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> >> Cc: Wen Xiong <wenxiong at us.ibm.com>
> >> Cc: Baoquan He <bhe at redhat.com>
> >> Cc: Ming Lei <ming.lei at redhat.com>
> >> Cc: Sourabh Jain <sourabhjain at linux.ibm.com>
> >> Cc: Hari Bathini <hbathini at linux.ibm.com>
> >> Cc: kexec at lists.infradead.org
> >> To: linuxppc-dev at lists.ozlabs.org
> >
> > Thanks for working on this, Pingfan.
> > Looks good to me.
> >
> > Acked-by: Hari Bathini <hbathini at linux.ibm.com>
> >
>
> On second thoughts, probably better off with no impact for
> bootcpu < nr_cpu_ids case and changing only two cores logical
> numbering otherwise. Something like the below (Please share
> your thoughts):
>

I am afraid that it may not be as ideal as it looks, considering the
following factors:
-1. For the case of 'bootcpu < nr_cpu_ids', crash can happen evenly
across any cpu in the system, which seriously undermines the
protection intended here (Under the most optimistic scenario, there is
a 50% chance of success)

-2. For the re-ordering of logical numbering, IMHO, if there is
concern that re-ordering will break something, the partial re-ordering
can not avoid that.  We ought to spot probable hazards so as to ease
worries.


Thanks,

Pingfan

> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index ec82f5bda908..78a8312aa8c4 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -76,7 +76,9 @@ u64 ppc64_rma_size;
>   unsigned int boot_cpu_node_count __ro_after_init;
>   #endif
>   static phys_addr_t first_memblock_size;
> +#ifdef CONFIG_SMP
>   static int __initdata boot_cpu_count;
> +#endif
>
>   static int __init early_parse_mem(char *p)
>   {
> @@ -357,6 +359,25 @@ static int __init early_init_dt_scan_cpus(unsigned
> long node,
>                         fdt_boot_cpuid_phys(initial_boot_params)) {
>                         found = boot_cpu_count;
>                         found_thread = i;
> +                       /*
> +                        * Map boot-cpu logical id into the range
> +                        * of [0, thread_per_core) if it can't be
> +                        * accommodated within nr_cpu_ids.
> +                        */
> +                       if (i != boot_cpu_count && boot_cpu_count >= nr_cpu_ids) {
> +                               boot_cpuid = i;
> +                               DBG("Logical CPU number for boot CPU changed from %d to %d\n",
> +                                   boot_cpu_count, i);
> +                       } else {
> +                               boot_cpuid = boot_cpu_count;
> +                       }
> +
> +                       /* Ensure boot thread is acconted for in nr_cpu_ids */
> +                       if (boot_cpuid >= nr_cpu_ids) {
> +                               set_nr_cpu_ids(boot_cpuid + 1);
> +                               DBG("Adjusted nr_cpu_ids to %u, to include boot CPU.\n",
> +                                   nr_cpu_ids);
> +                       }
>                 }
>   #ifdef CONFIG_SMP
>                 /* logical cpu id is always 0 on UP kernels */
> @@ -368,9 +389,8 @@ static int __init early_init_dt_scan_cpus(unsigned
> long node,
>         if (found < 0)
>                 return 0;
>
> -       DBG("boot cpu: logical %d physical %d\n", found,
> +       DBG("boot cpu: logical %d physical %d\n", boot_cpuid,
>             be32_to_cpu(intserv[found_thread]));
> -       boot_cpuid = found;
>
>         boot_cpu_hwid = be32_to_cpu(intserv[found_thread]);
>
> diff --git a/arch/powerpc/kernel/setup-common.c
> b/arch/powerpc/kernel/setup-common.c
> index b7b733474b60..f7179525c774 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -409,6 +409,12 @@ static void __init cpu_init_thread_core_maps(int tpc)
>
>   u32 *cpu_to_phys_id = NULL;
>
> +struct interrupt_server_node {
> +       bool    avail;
> +       int     len;
> +       __be32 intserv[];
> +};
> +
>   /**
>    * setup_cpu_maps - initialize the following cpu maps:
>    *                  cpu_possible_mask
> @@ -429,9 +435,13 @@ u32 *cpu_to_phys_id = NULL;
>    */
>   void __init smp_setup_cpu_maps(void)
>   {
> +       struct interrupt_server_node *core0_node = NULL, *bt_node = NULL;
> +       int orig_boot_cpu = -1, orig_boot_thread = -1;
> +       bool found_boot_cpu = false;
>         struct device_node *dn;
> -       int cpu = 0;
>         int nthreads = 1;
> +       int cpu = 0;
> +       int j, len;
>
>         DBG("smp_setup_cpu_maps()\n");
>
> @@ -442,9 +452,9 @@ void __init smp_setup_cpu_maps(void)
>                       __func__, nr_cpu_ids * sizeof(u32), __alignof__(u32));
>
>         for_each_node_by_type(dn, "cpu") {
> +               bool avail, skip = false;
>                 const __be32 *intserv;
>                 __be32 cpu_be;
> -               int j, len;
>
>                 DBG("  * %pOF...\n", dn);
>
> @@ -466,29 +476,121 @@ void __init smp_setup_cpu_maps(void)
>
>                 nthreads = len / sizeof(int);
>
> -               for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> -                       bool avail;
> +               avail = of_device_is_available(dn);
> +               if (!avail)
> +                       avail = !of_property_match_string(dn,
> +                                       "enable-method", "spin-table");
> +
> +               for (j = 0; (cpu == 0 || !found_boot_cpu) && j < nthreads; j++) {
> +                       if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
> +                               found_boot_cpu = true;
> +                               if (cpu == 0)
> +                                       break;
> +
> +                               /* Original logical CPU number of thread0 in boot core */
> +                               orig_boot_cpu = cpu;
> +                               orig_boot_thread = j;
> +                               bt_node = memblock_alloc(sizeof(struct interrupt_server_node) + len,
> +                                               __alignof__(u32));
> +                               if (!bt_node)
> +                                       panic("%s: Failed to allocate %zu bytes align=0x%zx\n",
> +                                               __func__,
> +                                               sizeof(struct interrupt_server_node) + len,
> +                                               __alignof__(u32));
> +                               bt_node->len = len;
> +                               memcpy(bt_node->intserv, intserv, len);
> +                               bt_node->avail = avail;
> +                               skip = true;
> +                               break;
> +                       }
> +               }
>
> +               /*
> +                * Boot CPU not on core0.
> +                * Hold off adding core0 until boot core is found as core0
> +                * may have to be replaced with boot core if boot core can
> +                * not be accommodated within nr_cpu_ids with its original
> +                * logical CPU numbering.
> +                */
> +               if (cpu == 0 && !found_boot_cpu) {
> +                       core0_node = memblock_alloc(sizeof(struct interrupt_server_node) + len,
> +                                       __alignof__(u32));
> +                       if (!core0_node)
> +                               panic("%s: Failed to allocate %zu bytes align=0x%zx\n",
> +                                       __func__,
> +                                       sizeof(struct interrupt_server_node) + len,
> +                                       __alignof__(u32));
> +                       core0_node->len = len;
> +                       memcpy(core0_node->intserv, intserv, len);
> +                       core0_node->avail = avail;
> +                       skip = true;
> +               }
> +
> +               if (skip) {
> +                       /* Assumes same number of threads for all cores */
> +                       cpu += nthreads;
> +                       continue;
> +               }
> +
> +               for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>                         DBG("    thread %d -> cpu %d (hard id %d)\n",
>                             j, cpu, be32_to_cpu(intserv[j]));
>
> -                       avail = of_device_is_available(dn);
> -                       if (!avail)
> -                               avail = !of_property_match_string(dn,
> -                                               "enable-method", "spin-table");
> -
>                         set_cpu_present(cpu, avail);
>                         set_cpu_possible(cpu, true);
>                         cpu_to_phys_id[cpu] = be32_to_cpu(intserv[j]);
>                         cpu++;
>                 }
>
> -               if (cpu >= nr_cpu_ids) {
> +               if (found_boot_cpu && cpu >= nr_cpu_ids) {
>                         of_node_put(dn);
>                         break;
>                 }
>         }
>
> +       /*
> +        * Boot CPU not on core0.
> +        *
> +        * If nr_cpu_ids does not accommodate the original logical CPU
> numbering for
> +        * boot CPU core, use logical CPU numbers 0 to nthreads for boot CPU core.
> +        * Note that boot cpu is already assigned with logical CPU number
> somewhere
> +        * between 0 to nthreads (depending on the boot thread within the core) in
> +        * early_init_dt_scan_cpus() for this case.
> +        *
> +        * Otherwise, stick with the original logical CPU numbering.
> +        */
> +       if (bt_node) {
> +               int core0_cpu;
> +
> +               if (orig_boot_cpu + orig_boot_thread >= nr_cpu_ids) {
> +                       cpu = 0;
> +                       core0_cpu = orig_boot_cpu;
> +               } else {
> +                       cpu = orig_boot_cpu;
> +                       core0_cpu = 0;
> +               }
> +
> +               for (j = 0; j < nthreads && core0_cpu < nr_cpu_ids; j++) {
> +                       DBG("    thread %d -> cpu %d (hard id %d)\n",
> +                           j, core0_cpu, be32_to_cpu(core0_node->intserv[j]));
> +
> +                       set_cpu_present(core0_cpu, core0_node->avail);
> +                       set_cpu_possible(core0_cpu, true);
> +                       cpu_to_phys_id[core0_cpu] = be32_to_cpu(core0_node->intserv[j]);
> +                       core0_cpu++;
> +               }
> +
> +               for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> +                       DBG("    thread %d -> cpu %d (hard id %d)\n",
> +                           j, cpu, be32_to_cpu(bt_node->intserv[j]));
> +
> +                       set_cpu_present(cpu, bt_node->avail);
> +                       set_cpu_possible(cpu, true);
> +                       cpu_to_phys_id[cpu] = be32_to_cpu(bt_node->intserv[j]);
> +                       cpu++;
> +               }
> +       }
> +
>         /* If no SMT supported, nthreads is forced to 1 */
>         if (!cpu_has_feature(CPU_FTR_SMT)) {
>                 DBG("  SMT disabled ! nthreads forced to 1\n");
>



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