Messages in this thread Patch in this message | | | From | Kuppuswamy Sathyanarayanan <> | Subject | [PATCH v2] x86/tdx: Don't write CSTAR MSR on Intel | Date | Thu, 18 Nov 2021 19:58:03 -0800 |
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From: Andi Kleen <ak@linux.intel.com>
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.
Signed-off-by: Andi Kleen <ak@linux.intel.com> Reviewed-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> ---
Changes since v1: * Made wrmsrl_cstar() static.
arch/x86/kernel/cpu/common.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0083464de5e3..c3bb03201f2a 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1787,6 +1787,18 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count); DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = TOP_OF_INIT_STACK; +/* Don't write CSTAR MSR on Intel platforms */ +static void wrmsrl_cstar(unsigned long val) +{ + /* + * Intel CPUs do not support 32-bit SYSCALL. Writing to MSR_CSTAR + * is normally ignored by the CPU, but raises a #VE trap in a TDX + * guest. + */ + 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 +1806,7 @@ 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 +1818,7 @@ 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); -- 2.25.1
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