Re: [PATCH v3 05/10] xen/arm: Setup virtual paging for non-boot CPUs on hotplug/resume

[Julien Grall <julien.grall@arm.com>]

Hi Mirela,

On 27/04/18 18:12, Mirela Simonovic wrote:
> In existing code the virtual paging for non-boot CPUs is setup only on boot.
> The setup is triggered from start_xen() after all CPUs are brought online.
> In other words, the initialization of VTCR_EL2 register is done out of the
> cpu_up/start_secondary() control flow. However, the cpu_up flow is also used
> to hotplug non-boot CPUs on resume from suspend to RAM state, in which case
> the virtual paging will not be configured.
> 
> With this patch the setting of paging is triggered from start_secondary()
> function using cpu starting notifier (notify_cpu_starting() call). The
> notifier is registered in p2m.c using init call. This has to be done with
> init call rather than presmp_init because the registered callback depends
> on vtcr configuration value which is setup after the presmp init calls
> are executed (do_presmp_initcalls() called from start_xen()). Init calls
> are executed after initial virtual paging is set up for all CPUs on boot.
> This ensures that no callback can fire until the vtcr value is calculated
> by Xen and virtual paging is set up initially for all CPUs. Also, this way
> the virtual paging setup in boot scenario remains unchanged.
> 
> It is assumed here that after the system completed the boot, CPUs that
> execute start_secondary() were booted as well when the Xen itself was
> booted. According to this assumption non-boot CPUs will always be compliant
> with the VTCR_EL2 value that was selected by Xen on boot.
> Currently, there is no mechanism to trigger hotplugging of a CPU. This
> will be added with the suspend to RAM support for ARM, where the hotplug
> of non-boot CPUs will be triggered via enable_nonboot_cpus() call.
> 
> Signed-off-by: Mirela Simonovic <mirela.simonovic@aggios.com>
> 
> ---
> CC: Stefano Stabellini <sstabellini@kernel.org>
> CC: Julien Grall <julien.grall@arm.com>
> ---
> Changes in v2:
> -Fix commit message
> -Save configured VTCR_EL2 value into static variable that will be used
>   by non-boot CPUs on hotplug
> -Add setup_virt_paging_secondary() and invoke it from start_secondary()
>   if that CPU has to setup virtual paging (if the system state is not boot)
> 
> Changes in v3:
> -Fix commit message
> -Remove setup_virt_paging_secondary() and use notifier to setup virtual
>   paging for non-boot CPU on hotplug.
> -In setup_virt_paging() use vtcr static variable instead of local val
> -In setup_virt_paging_one() use vtcr static variable instead of provided
>   argument
> ---
>   xen/arch/arm/p2m.c | 82 +++++++++++++++++++++++++++++++++++++++++-------------
>   1 file changed, 62 insertions(+), 20 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index d43c3aa896..98a1fe6de9 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -8,6 +8,8 @@
>   #include <xen/iocap.h>
>   #include <xen/mem_access.h>
>   #include <xen/xmalloc.h>
> +#include <xen/notifier.h>
> +#include <xen/cpu.h>

Please add them alphabetically.

>   #include <public/vm_event.h>
>   #include <asm/flushtlb.h>
>   #include <asm/event.h>
> @@ -1451,24 +1453,17 @@ err:
>       return page;
>   }
>   
> -static void __init setup_virt_paging_one(void *data)
> +/* VTCR value to be configured by all CPUs. Set only once by the boot CPU */
> +static uint64_t __read_mostly vtcr;
> +
> +static void setup_virt_paging_one(void *data)
>   {
> -    unsigned long val = (unsigned long)data;
> -    WRITE_SYSREG32(val, VTCR_EL2);
> +    WRITE_SYSREG32(vtcr, VTCR_EL2);
>       isb();
>   }
>   
>   void __init setup_virt_paging(void)
>   {
> -    /* Setup Stage 2 address translation */
> -    unsigned long val = VTCR_RES1|VTCR_SH0_IS|VTCR_ORGN0_WBWA|VTCR_IRGN0_WBWA;
> -
> -#ifdef CONFIG_ARM_32
> -    printk("P2M: 40-bit IPA\n");
> -    p2m_ipa_bits = 40;
> -    val |= VTCR_T0SZ(0x18); /* 40 bit IPA */
> -    val |= VTCR_SL0(0x1); /* P2M starts at first level */
> -#else /* CONFIG_ARM_64 */
>       const struct {
>           unsigned int pabits; /* Physical Address Size */
>           unsigned int t0sz;   /* Desired T0SZ, minimum in comment */
> @@ -1491,6 +1486,16 @@ void __init setup_virt_paging(void)
>       unsigned int pa_range = 0x10; /* Larger than any possible value */
>       bool vmid_8_bit = false;

That's not going to build on arm32 because vmid_8_bit & co are not used. 
While I will not ask you to test the changes on 32-bit board, I would at 
least want each change to be build test it on impacted architecture.

In that particular case, you can just move the initialization of vtcr at 
after the endif because there is nothing that required that to be setup 
very early.

>   
> +    /* Setup Stage 2 address translation */
> +    vtcr = VTCR_RES1|VTCR_SH0_IS|VTCR_ORGN0_WBWA|VTCR_IRGN0_WBWA;
> +
> +#ifdef CONFIG_ARM_32
> +    printk("P2M: 40-bit IPA\n");
> +    p2m_ipa_bits = 40;
> +    vtcr |= VTCR_T0SZ(0x18); /* 40 bit IPA */
> +    vtcr |= VTCR_SL0(0x1); /* P2M starts at first level */
> +#else /* CONFIG_ARM_64 */
> +
>       for_each_online_cpu ( cpu )
>       {
>           const struct cpuinfo_arm *info = &cpu_data[cpu];
> @@ -1513,14 +1518,14 @@ void __init setup_virt_paging(void)
>       if ( pa_range >= ARRAY_SIZE(pa_range_info) || !pa_range_info[pa_range].pabits )
>           panic("Unknown encoding of ID_AA64MMFR0_EL1.PARange %x\n", pa_range);
>   
> -    val |= VTCR_PS(pa_range);
> -    val |= VTCR_TG0_4K;
> +    vtcr |= VTCR_PS(pa_range);
> +    vtcr |= VTCR_TG0_4K;
>   
>       /* Set the VS bit only if 16 bit VMID is supported. */
>       if ( MAX_VMID == MAX_VMID_16_BIT )
> -        val |= VTCR_VS;
> -    val |= VTCR_SL0(pa_range_info[pa_range].sl0);
> -    val |= VTCR_T0SZ(pa_range_info[pa_range].t0sz);
> +        vtcr |= VTCR_VS;
> +    vtcr |= VTCR_SL0(pa_range_info[pa_range].sl0);
> +    vtcr |= VTCR_T0SZ(pa_range_info[pa_range].t0sz);
>   
>       p2m_root_order = pa_range_info[pa_range].root_order;
>       p2m_root_level = 2 - pa_range_info[pa_range].sl0;
> @@ -1532,16 +1537,53 @@ void __init setup_virt_paging(void)
>              ( MAX_VMID == MAX_VMID_16_BIT ) ? 16 : 8);
>   #endif
>       printk("P2M: %d levels with order-%d root, VTCR 0x%lx\n",
> -           4 - P2M_ROOT_LEVEL, P2M_ROOT_ORDER, val);
> +           4 - P2M_ROOT_LEVEL, P2M_ROOT_ORDER, vtcr);
>   
>       p2m_vmid_allocator_init();
>   
>       /* It is not allowed to concatenate a level zero root */
>       BUG_ON( P2M_ROOT_LEVEL == 0 && P2M_ROOT_ORDER > 0 );
> -    setup_virt_paging_one((void *)val);
> -    smp_call_function(setup_virt_paging_one, (void *)val, 1);
> +    setup_virt_paging_one(NULL);
> +    smp_call_function(setup_virt_paging_one, NULL, 1);
> +}
> +
> +static int cpu_virt_paging_callback(
> +    struct notifier_block *nfb, unsigned long action, void *hcpu)

The indentation looks wrong.

> +{
> +    switch ( action )
> +    {
> +    case CPU_STARTING:
> +        ASSERT(system_state != SYS_STATE_boot);

I was about to complain about this but then saw you add the notifiers 
after. That's quite clever and the comment is really helpful :).

> +        setup_virt_paging_one(NULL);
> +        break;
> +    default:
> +        break;
> +    }
> +
> +    return NOTIFY_DONE;
>   }
>   
> +static struct notifier_block cpu_virt_paging_nfb = {
> +    .notifier_call = cpu_virt_paging_callback,
> +    .priority = 100 /* highest priority */
> +};
> +
> +static int __init cpu_virt_paging_init(void)
> +{
> +    register_cpu_notifier(&cpu_virt_paging_nfb);
> +    return 0;
> +}

NIT: Missing newline.

> +/*
> + * Initialization of the notifier has to be done at init rather than presmp_init
> + * phase because: the registered notifier is used to setup virtual paging for
> + * non-boot CPUs after the initial virtual paging for all CPUs is already setup,
> + * i.e. when a non-boot CPU is hotplugged after the system has booted. In other
> + * words, the notifier should be registered after the virtual paging is
> + * initially setup (setup_virt_paging() is called from start_xen()). This is
> + * required because vtcr config value has to be set before a notifier can fire.
> + */
> +__initcall(cpu_virt_paging_init);
> +
>   /*
>    * Local variables:
>    * mode: C
> 

Cheers,

-- 
Julien Grall

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