RE: [PATCH v2] x86/hyperv: Use per cpu initial stack for vtl context

[Michael Kelley]

From: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, February 1, 2024 11:13 PM
> 
> Currently, the secondary CPUs in Hyper-V VTL context lack support for
> parallel startup. Therefore, relying on the single initial_stack fetched
> from the current task structure suffices for all vCPUs.
> 
> However, common initial_stack risks stack corruption when parallel startup
> is enabled. In order to facilitate parallel startup, use the initial_stack
> from the per CPU idle thread instead of the current task.
> 
> Fixes: 18415f33e2ac ("cpu/hotplug: Allow "parallel" bringup up to CPUHP_BP_KICK_AP_STATE")
> Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> ---
>  arch/x86/hyperv/hv_vtl.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 96e6c51515f5..b0ab724def17 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -12,6 +12,7 @@
>  #include <asm/i8259.h>
>  #include <asm/mshyperv.h>
>  #include <asm/realmode.h>
> +#include <../kernel/smpboot.h>
> 
>  extern struct boot_params boot_params;
>  static struct real_mode_header hv_vtl_real_mode_header;
> @@ -57,7 +58,7 @@ static void hv_vtl_ap_entry(void)
>  	((secondary_startup_64_fn)secondary_startup_64)(&boot_params, &boot_params);
>  }
> 
> -static int hv_vtl_bringup_vcpu(u32 target_vp_index, u64 eip_ignored)
> +static int hv_vtl_bringup_vcpu(u32 target_vp_index, int cpu, u64 eip_ignored)
>  {
>  	u64 status;
>  	int ret = 0;
> @@ -71,7 +72,8 @@ static int hv_vtl_bringup_vcpu(u32 target_vp_index, u64 eip_ignored)
>  	struct ldttss_desc *ldt;
>  	struct desc_struct *gdt;
> 
> -	u64 rsp = current->thread.sp;
> +	struct task_struct *idle = idle_thread_get(cpu);
> +	u64 rsp = (unsigned long)idle->thread.sp;
>  	u64 rip = (u64)&hv_vtl_ap_entry;
> 
>  	native_store_gdt(&gdt_ptr);
> @@ -198,7 +200,15 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
> 
>  static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
>  {
> -	int vp_id;
> +	int vp_id, cpu;
> +
> +	/* Find the logical CPU for the APIC ID */
> +	for_each_present_cpu(cpu) {
> +		if (arch_match_cpu_phys_id(cpu, apicid))
> +			break;
> +	}
> +	if (cpu >= nr_cpu_ids)
> +		return -EINVAL;
> 
>  	pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
>  	vp_id = hv_vtl_apicid_to_vp_id(apicid);
> @@ -212,7 +222,7 @@ static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
>  		return -EINVAL;
>  	}
> 
> -	return hv_vtl_bringup_vcpu(vp_id, start_eip);
> +	return hv_vtl_bringup_vcpu(vp_id, cpu, start_eip);
>  }
> 
>  int __init hv_vtl_early_init(void)
> --
> 2.34.1
> 

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>