Patch "x86/hyperv: Use per cpu initial stack for vtl context" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    x86/hyperv: Use per cpu initial stack for vtl context

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-hyperv-use-per-cpu-initial-stack-for-vtl-context.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6d3b54ec6f75b0ad202c6cdb9e242cf7f6dde5d9
Author: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
Date:   Sun Mar 3 00:01:36 2024 -0800

    x86/hyperv: Use per cpu initial stack for vtl context
    
    [ Upstream commit 2b4b90e053a29057fb05ba81acce26bddce8d404 ]
    
    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: 3be1bc2fe9d2 ("x86/hyperv: VTL support for Hyper-V")
    Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
    Link: https://lore.kernel.org/r/1709452896-13342-1-git-send-email-ssengar@xxxxxxxxxxxxxxxxxxx
    Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
    Message-ID: <1709452896-13342-1-git-send-email-ssengar@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 53b309d41b3b9..c2f78fabc865b 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;
@@ -64,7 +65,7 @@ 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;
@@ -78,7 +79,9 @@ 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);
@@ -205,7 +208,15 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
 
 static int hv_vtl_wakeup_secondary_cpu(int 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);
@@ -219,7 +230,7 @@ static int hv_vtl_wakeup_secondary_cpu(int 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)
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 00242107d62e0..862c47b191afe 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -16,6 +16,7 @@ config HYPERV
 config HYPERV_VTL_MODE
 	bool "Enable Linux to boot in VTL context"
 	depends on X86_64 && HYPERV
+	depends on SMP
 	default n
 	help
 	  Virtual Secure Mode (VSM) is a set of hypervisor capabilities and




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