linux-kernel - [RFC v2 24/32] x86/topology: Disable CPU online/offline control for TDX guest

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Date:   Mon, 26 Apr 2021 11:01:51 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: [RFC v2 24/32] x86/topology: Disable CPU online/offline control for TDX guest

As per Intel TDX Virtual Firmware Design Guide, sec 4.3.5 and
sec 9.4, all unused CPUs are put in spinning state by
TDVF until OS requests for CPU bring-up via mailbox address passed
by ACPI MADT table. Since by default all unused CPUs are always in
spinning state, there is no point in supporting dynamic CPU
online/offline feature. So current generation of TDVF does not
support CPU hotplug feature. It may be supported in next generation.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/tdx.c      | 14 ++++++++++++++
 arch/x86/kernel/topology.c |  3 ++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 294dda5bf3f6..ab1efa4d10e9 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -316,6 +316,17 @@ static int tdg_handle_mmio(struct pt_regs *regs, struct ve_info *ve)
 	return insn.length;
 }
 
+static int tdg_cpu_offline_prepare(unsigned int cpu)
+{
+	/*
+	 * Per Intel TDX Virtual Firmware Design Guide,
+	 * sec 4.3.5 and sec 9.4, Hotplug is not supported
+	 * in TDX platforms. So don't support CPU
+	 * offline feature once its turned on.
+	 */
+	return -EOPNOTSUPP;
+}
+
 unsigned long tdg_get_ve_info(struct ve_info *ve)
 {
 	u64 ret;
@@ -410,5 +421,8 @@ void __init tdx_early_init(void)
 	pv_ops.irq.safe_halt = tdg_safe_halt;
 	pv_ops.irq.halt = tdg_halt;
 
+	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "tdg:cpu_hotplug",
+			  NULL, tdg_cpu_offline_prepare);
+
 	pr_info("TDX guest is initialized\n");
 }
diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index f5477eab5692..d879ea96d79c 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -34,6 +34,7 @@
 #include <linux/irq.h>
 #include <asm/io_apic.h>
 #include <asm/cpu.h>
+#include <asm/tdx.h>
 
 static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
 
@@ -130,7 +131,7 @@ int arch_register_cpu(int num)
 			}
 		}
 	}
-	if (num || cpu0_hotpluggable)
+	if ((num || cpu0_hotpluggable) && !is_tdx_guest())
 		per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
 
 	return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
-- 
2.25.1