x86/cpu: Don't write CSTAR MSR on Intel CPUs

Intel CPUs do not support SYSCALL in 32-bit mode, but the kernel
initializes MSR_CSTAR unconditionally. That MSR write is normally
ignored by the CPU, but in a TDX guest it raises a #VE trap.

Exclude Intel CPUs from the MSR_CSTAR initialization.

[ tglx: Fixed the subject line and removed the redundant comment. ]

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20211119035803.4012145-1-sathyanarayanan.kuppuswamy@linux.intel.com

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0083464..0663642 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1787,6 +1787,17 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count);
 
 DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = TOP_OF_INIT_STACK;
 
+static void wrmsrl_cstar(unsigned long val)
+{
+       /*
+        * Intel CPUs do not support 32-bit SYSCALL. Writing to MSR_CSTAR
+        * is so far ignored by the CPU, but raises a #VE trap in a TDX
+        * guest. Avoid the pointless write on all Intel CPUs.
+        */
+       if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+               wrmsrl(MSR_CSTAR, val);
+}
+
 /* May not be marked __init: used by software suspend */
 void syscall_init(void)
 {
@@ -1794,7 +1805,7 @@ void syscall_init(void)
        wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);
 
 #ifdef CONFIG_IA32_EMULATION
-       wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
+       wrmsrl_cstar((unsigned long)entry_SYSCALL_compat);
        /*
         * This only works on Intel CPUs.
         * On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP.
@@ -1806,7 +1817,7 @@ void syscall_init(void)
                    (unsigned long)(cpu_entry_stack(smp_processor_id()) + 1));
        wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
 #else
-       wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
+       wrmsrl_cstar((unsigned long)ignore_sysret);
        wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
        wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
        wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);