linux-kernel - [PATCH] x86/hyperv: Use per cpu initial stack for vtl context

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Date: Thu,  1 Feb 2024 10:25:31 -0800
From: Saurabh Sengar <ssengar@...ux.microsoft.com>
To: kys@...rosoft.com,
	haiyangz@...rosoft.com,
	wei.liu@...nel.org,
	decui@...rosoft.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	dwmw@...zon.co.uk,
	peterz@...radead.org,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: ssengar@...rosoft.com
Subject: [PATCH] x86/hyperv: Use per cpu initial stack for vtl context

Currently, the secondary vCPUs 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@...ux.microsoft.com>
---
 arch/x86/hyperv/hv_vtl.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 96e6c51515f5..a54b46b673de 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;
@@ -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(target_vp_index);
+	u64 rsp = (unsigned long)idle->thread.sp;
 	u64 rip = (u64)&hv_vtl_ap_entry;
 
 	native_store_gdt(&gdt_ptr);
-- 
2.34.1