Commit 9c7e2634 authored by Andi Kleen's avatar Andi Kleen Committed by Thomas Gleixner
Browse files

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: default avatarAndi Kleen <ak@linux.intel.com>
Signed-off-by: default avatarKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20211119035803.4012145-1-sathyanarayanan.kuppuswamy@linux.intel.com
parent 13605725

arch/x86/kernel/cpu/common.c

+13 −2
Original line number Diff line number Diff line
@@ -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);