Hi Hari,
On Mon, Nov 27, 2023 at 12:30 PM Hari Bathini <hbathini@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
> >> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> >> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> >> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> >> Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
> >> Cc: Wen Xiong <wenxiong@xxxxxxxxxx>
> >> Cc: Baoquan He <bhe@xxxxxxxxxx>
> >> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> >> Cc: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
> >> Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> >> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> >> To: linuxppc-dev@xxxxxxxxxxxxxxxx
> >
> > Thanks for working on this, Pingfan.
> > Looks good to me.
> >
> > Acked-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> >
>
> 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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