Merge tag 'x86-fred-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 FRED updates from Thomas Gleixner:

 - Enable FRED right after init_mem_mapping() because at that point the
   early IDT fault handler is replaced by the real fault handler. The
   real fault handler retrieves the faulting address from the stack
   frame and not from CR2 when the FRED feature is set. But that
   obviously only works when FRED is enabled in the CPU as well.

 - Set SS to __KERNEL_DS when enabling FRED to prevent a corner case
   where ERETS can observe a SS mismatch and raises a #GP.

* tag 'x86-fred-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/entry: Set FRED RSP0 on return to userspace instead of context switch
  x86/msr: Switch between WRMSRNS and WRMSR with the alternatives mechanism
  x86/entry: Test ti_work for zero before processing individual bits
  x86/fred: Set SS to __KERNEL_DS when enabling FRED
  x86/fred: Enable FRED right after init_mem_mapping()
  x86/fred: Move FRED RSP initialization into a separate function
  x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

1 files changed, 1 insertions, 27 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 415881607c5d..d05392db5d0f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1451,34 +1451,8 @@ DEFINE_IDTENTRY_SW(iret_error)
 }
 #endif
 
-/* Do not enable FRED by default yet. */
-static bool enable_fred __ro_after_init = false;
-
-#ifdef CONFIG_X86_FRED
-static int __init fred_setup(char *str)
-{
-	if (!str)
-		return -EINVAL;
-
-	if (!cpu_feature_enabled(X86_FEATURE_FRED))
-		return 0;
-
-	if (!strcmp(str, "on"))
-		enable_fred = true;
-	else if (!strcmp(str, "off"))
-		enable_fred = false;
-	else
-		pr_warn("invalid FRED option: 'fred=%s'\n", str);
-	return 0;
-}
-early_param("fred", fred_setup);
-#endif
-
 void __init trap_init(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
-		setup_clear_cpu_cap(X86_FEATURE_FRED);
-
 	/* Init cpu_entry_area before IST entries are set up */
 	setup_cpu_entry_areas();
 
@@ -1486,7 +1460,7 @@ void __init trap_init(void)
 	sev_es_init_vc_handling();
 
 	/* Initialize TSS before setting up traps so ISTs work */
-	cpu_init_exception_handling();
+	cpu_init_exception_handling(true);
 
 	/* Setup traps as cpu_init() might #GP */
 	if (!cpu_feature_enabled(X86_FEATURE_FRED))