linux-kernel - [PATCH v3 3/5] x86/topology: Disable CPU online/offline control for TDX guest

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Message-Id: <20210720040901.2121268-4-sathyanarayanan.kuppuswamy@linux.intel.com>
Date:   Mon, 19 Jul 2021 21:08:59 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Peter H Anvin <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/5] 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>
---

Changes since v1:
 * Replaced is_tdx_guest() check with prot_guest_has(PR_GUEST_TDX).

 arch/x86/kernel/tdx.c      | 15 +++++++++++++++
 arch/x86/kernel/topology.c |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 92acccbce59c..a110bd5e5e4c 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -5,6 +5,7 @@
 #define pr_fmt(fmt)     "x86/tdx: " fmt
 
 #include <linux/protected_guest.h>
+#include <linux/cpuhotplug.h>
 
 #include <asm/tdx.h>
 #include <asm/vmx.h>
@@ -306,6 +307,17 @@ 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 it is turned on.
+	 */
+	return -EOPNOTSUPP;
+}
+
 unsigned long tdg_get_ve_info(struct ve_info *ve)
 {
 	u64 ret;
@@ -446,5 +458,8 @@ 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("Guest initialized\n");
 }
diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index bd83748e2bde..7b5fab69d56e 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -32,6 +32,7 @@
 #include <linux/init.h>
 #include <linux/smp.h>
 #include <linux/irq.h>
+#include <linux/protected_guest.h>
 #include <asm/io_apic.h>
 #include <asm/cpu.h>
 
@@ -130,7 +131,7 @@ int arch_register_cpu(int num)
 			}
 		}
 	}
-	if (num || cpu0_hotpluggable)
+	if ((num || cpu0_hotpluggable) && !prot_guest_has(PR_GUEST_TDX))
 		per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
 
 	return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
-- 
2.25.1