[tip: x86/cpu] x86/fpu: Remove MATH_EMULATION and related glue code

["tip-bot2 for Ingo Molnar" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     ab05214025ee2af262591cd48df17883648bdb1a
Gitweb:        https://git.kernel.org/tip/ab05214025ee2af262591cd48df17883648bdb1a
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Thu, 15 May 2025 10:28:27 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 08 May 2026 07:33:03 +02:00

x86/fpu: Remove MATH_EMULATION and related glue code

Now that support for 486 CPUs is gone upstream, remove
the x86 mathemu code integration.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250425084216.3913608-9-mingo@kernel.org
---
 arch/x86/Kconfig               | 27 ---------------------------
 arch/x86/Kconfig.cpufeatures   |  1 -
 arch/x86/Makefile              |  1 -
 arch/x86/include/asm/fpu/api.h |  6 ------
 arch/x86/kernel/fpu/core.c     |  5 -----
 arch/x86/kernel/fpu/init.c     |  9 +--------
 arch/x86/kernel/traps.c        | 14 --------------
 7 files changed, 1 insertion(+), 62 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6865471..f67af15 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1633,33 +1633,6 @@ config X86_BOOTPARAM_MEMORY_CORRUPTION_CHECK
 	  Set whether the default state of memory_corruption_check is
 	  on or off.
 
-config MATH_EMULATION
-	bool
-	depends on MODIFY_LDT_SYSCALL
-	prompt "Math emulation" if X86_32 && (M486SX || MELAN)
-	help
-	  Linux can emulate a math coprocessor (used for floating point
-	  operations) if you don't have one. 486DX and Pentium processors have
-	  a math coprocessor built in, 486SX and 386 do not, unless you added
-	  a 487DX or 387, respectively. (The messages during boot time can
-	  give you some hints here ["man dmesg"].) Everyone needs either a
-	  coprocessor or this emulation.
-
-	  If you don't have a math coprocessor, you need to say Y here; if you
-	  say Y here even though you have a coprocessor, the coprocessor will
-	  be used nevertheless. (This behavior can be changed with the kernel
-	  command line option "no387", which comes handy if your coprocessor
-	  is broken. Try "man bootparam" or see the documentation of your boot
-	  loader (lilo or loadlin) about how to pass options to the kernel at
-	  boot time.) This means that it is a good idea to say Y here if you
-	  intend to use this kernel on different machines.
-
-	  More information about the internals of the Linux math coprocessor
-	  emulation can be found in <file:arch/x86/math-emu/README>.
-
-	  If you are not sure, say Y; apart from resulting in a 66 KB bigger
-	  kernel, it won't hurt.
-
 config MTRR
 	def_bool y
 	prompt "MTRR (Memory Type Range Register) support" if EXPERT
diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
index 532cbc2..89cbf8f 100644
--- a/arch/x86/Kconfig.cpufeatures
+++ b/arch/x86/Kconfig.cpufeatures
@@ -70,7 +70,6 @@ config X86_REQUIRED_FEATURE_UP
 
 config X86_REQUIRED_FEATURE_FPU
 	def_bool y
-	depends on !MATH_EMULATION
 
 config X86_REQUIRED_FEATURE_PAE
 	def_bool y
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 46fec0b..96bfa13 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -276,7 +276,6 @@ archprepare: $(cpufeaturemasks.hdr)
 libs-y  += arch/x86/lib/
 
 # drivers-y are linked after core-y
-drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
 drivers-$(CONFIG_PCI)            += arch/x86/pci/
 
 # suspend and hibernation support
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index cd6f194..90c63fe 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -119,12 +119,6 @@ extern void fpu__init_system(void);
 extern void fpu__init_check_bugs(void);
 extern void fpu__resume_cpu(void);
 
-#ifdef CONFIG_MATH_EMULATION
-extern void fpstate_init_soft(struct swregs_state *soft);
-#else
-static inline void fpstate_init_soft(struct swregs_state *soft) {}
-#endif
-
 /* State tracking */
 DECLARE_PER_CPU(bool, kernel_fpu_allowed);
 DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 6089838..584fb99 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -558,11 +558,6 @@ static inline void fpstate_init_fstate(struct fpstate *fpstate)
  */
 void fpstate_init_user(struct fpstate *fpstate)
 {
-	if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
-		fpstate_init_soft(&fpstate->regs.soft);
-		return;
-	}
-
 	xstate_init_xcomp_bv(&fpstate->regs.xsave, fpstate->xfeatures);
 
 	if (cpu_feature_enabled(X86_FEATURE_FXSR))
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index ff988b9..0d33c21 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -36,12 +36,7 @@ static void fpu__init_cpu_generic(void)
 	write_cr0(cr0);
 
 	/* Flush out any pending x87 state: */
-#ifdef CONFIG_MATH_EMULATION
-	if (!boot_cpu_has(X86_FEATURE_FPU))
-		;
-	else
-#endif
-		asm volatile ("fninit");
+	asm volatile ("fninit");
 }
 
 /*
@@ -86,13 +81,11 @@ static void __init fpu__init_system_early_generic(void)
 			setup_clear_cpu_cap(X86_FEATURE_FPU);
 	}
 
-#ifndef CONFIG_MATH_EMULATION
 	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
 		pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
 		for (;;)
 			asm volatile("hlt");
 	}
-#endif
 }
 
 /*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 52177bc..30aa836 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1543,20 +1543,6 @@ DEFINE_IDTENTRY(exc_device_not_available)
 	if (handle_xfd_event(regs))
 		return;
 
-#ifdef CONFIG_MATH_EMULATION
-	if (!boot_cpu_has(X86_FEATURE_FPU) && (cr0 & X86_CR0_EM)) {
-		struct math_emu_info info = { };
-
-		cond_local_irq_enable(regs);
-
-		info.regs = regs;
-		math_emulate(&info);
-
-		cond_local_irq_disable(regs);
-		return;
-	}
-#endif
-
 	/* This should not happen. */
 	if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) {
 		/* Try to fix it up and carry on. */