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SubjectRe: [PATCH 2/2] irqchip/gic-v3-its: Move ITS' ->pend_page allocation into an early CPU up callback
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Hi Sebastian,

On 18/07/18 16:42, Sebastian Andrzej Siewior wrote:
> The AP-GIC-starting callback allocates memory for the ->pend_page while
> the CPU is started during boot-up. This callback is invoked on the
> target CPU with disabled interrupts.
> This does not work on -RT because memory allocations are not possible
> with disabled interrupts.
> Move the memory allocation to an earlier hotplug step which is invoked
> with enabled interrupts on the boot CPU.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> drivers/irqchip/irq-gic-v3-its.c | 60 ++++++++++++++++++++++----------
> 1 file changed, 41 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index a616043d25ee..acc3d44c356d 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -171,6 +171,7 @@ static DEFINE_RAW_SPINLOCK(vmovp_lock);
> static DEFINE_IDA(its_vpeid_ida);
>
> #define gic_data_rdist() (raw_cpu_ptr(gic_rdists->rdist))
> +#define gic_data_rdist_cpu(cpu) (per_cpu_ptr(gic_rdists->rdist, cpu))
> #define gic_data_rdist_rd_base() (gic_data_rdist()->rd_base)
> #define gic_data_rdist_vlpi_base() (gic_data_rdist_rd_base() + SZ_128K)
>
> @@ -1853,15 +1854,17 @@ static int its_alloc_collections(struct its_node *its)
> return 0;
> }
>
> -static struct page *its_allocate_pending_table(gfp_t gfp_flags)
> +static struct page *its_allocate_pending_table(unsigned int cpu)
> {
> struct page *pend_page;
> + unsigned int order;
> /*
> * The pending pages have to be at least 64kB aligned,
> * hence the 'max(LPI_PENDBASE_SZ, SZ_64K)' below.
> */
> - pend_page = alloc_pages(gfp_flags | __GFP_ZERO,
> - get_order(max_t(u32, LPI_PENDBASE_SZ, SZ_64K)));
> + order = get_order(max_t(u32, LPI_PENDBASE_SZ, SZ_64K));
> + pend_page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_ZERO,
> + order);
> if (!pend_page)
> return NULL;
>
> @@ -1877,6 +1880,28 @@ static void its_free_pending_table(struct page *pt)
> get_order(max_t(u32, LPI_PENDBASE_SZ, SZ_64K)));
> }
>
> +static int its_alloc_pend_page(unsigned int cpu)
> +{
> + struct page *pend_page;
> + phys_addr_t paddr;
> +
> + pend_page = gic_data_rdist_cpu(cpu)->pend_page;
> + if (pend_page)
> + return 0;
> +
> + pend_page = its_allocate_pending_table(cpu);
> + if (!pend_page) {
> + pr_err("Failed to allocate PENDBASE for CPU%d\n",
> + smp_processor_id());
> + return -ENOMEM;
> + }
> +
> + paddr = page_to_phys(pend_page);
> + pr_info("CPU%d: using LPI pending table @%pa\n", cpu, &paddr);
> + gic_data_rdist_cpu(cpu)->pend_page = pend_page;
> + return 0;
> +}
> +
> static void its_cpu_init_lpis(void)
> {
> void __iomem *rbase = gic_data_rdist_rd_base();
> @@ -1885,21 +1910,8 @@ static void its_cpu_init_lpis(void)
>
> /* If we didn't allocate the pending table yet, do it now */
> pend_page = gic_data_rdist()->pend_page;
> - if (!pend_page) {
> - phys_addr_t paddr;
> -
> - pend_page = its_allocate_pending_table(GFP_NOWAIT);
> - if (!pend_page) {
> - pr_err("Failed to allocate PENDBASE for CPU%d\n",
> - smp_processor_id());
> - return;
> - }
> -
> - paddr = page_to_phys(pend_page);
> - pr_info("CPU%d: using LPI pending table @%pa\n",
> - smp_processor_id(), &paddr);
> - gic_data_rdist()->pend_page = pend_page;
> - }
> + if (WARN_ON(!pend_page))
> + return;
>
> /* set PROPBASE */
> val = (page_to_phys(gic_rdists->prop_page) |
> @@ -2732,7 +2744,7 @@ static int its_vpe_init(struct its_vpe *vpe)
> return vpe_id;
>
> /* Allocate VPT */
> - vpt_page = its_allocate_pending_table(GFP_KERNEL);
> + vpt_page = its_allocate_pending_table(raw_smp_processor_id());
> if (!vpt_page) {
> its_vpe_id_free(vpe_id);
> return -ENOMEM;
> @@ -3706,6 +3718,16 @@ int __init its_init(struct fwnode_handle *handle, struct rdists *rdists,
> if (err)
> return err;
>
> + err = cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "irqchip/arm/gicv3:prepare",
> + its_alloc_pend_page, NULL);
> + if (err < 0) {
> + pr_warn("ITS: Can't register CPU-hoplug callback.\n");
> + return err;
> + }
> + err = its_alloc_pend_page(smp_processor_id());
> + if (err < 0)
> + return err;
> +
> list_for_each_entry(its, &its_nodes, entry)
> has_v4 |= its->is_v4;
>
>

I must say I'm not overly keen on the extra hotplug notifier, and I'd
rather allocate all the memory upfront on the boot CPU.

I've implemented this as part of a series that is required for
kexec/kdump support[1] (and specifically this[2] patch). Could you
please have a look and let me know if that works for you? I otherwise
plan to post it for review once the 4.19 merge window has closed.

Thanks,

M.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/gicv3-kdump
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=irq/gicv3-kdump&id=effe377d415900af10e206173d60dc6cc3f0662c
--
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