[tip: x86/fpu] x86/fpu: Remove unnecessary checks for X86_FEATURE_FPU
From: tip-bot2 for Eric Biggers
Date: Sat Sep 26 2026 - 01:54:27 EST
The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: 67639ee98521c1592190c5c67047067a9c3a3fd5
Gitweb: https://git.kernel.org/tip/67639ee98521c1592190c5c67047067a9c3a3fd5
Author: Eric Biggers <ebiggers@xxxxxxxxxx>
AuthorDate: Fri, 25 Sep 2026 21:30:07 -07:00
Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Fri, 25 Sep 2026 21:35:37 -07:00
x86/fpu: Remove unnecessary checks for X86_FEATURE_FPU
Since
ab05214025ee ("x86/fpu: Remove MATH_EMULATION and related glue code"),
X86_FEATURE_FPU is mandatory. If it's absent, the kernel halts execution in
fpu__init_system_early_generic().
Therefore, remove unnecessary checks for X86_FEATURE_FPU that occur later in
x86/fpu code.
This makes struct swregs_state and the extern declarations of fpregs_soft_get
and fpregs_soft_set all unused. So remove those too.
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://patch.msgid.link/20260924033405.57613-1-ebiggers@xxxxxxxxxx
---
arch/x86/include/asm/fpu/regset.h | 6 ++----
arch/x86/include/asm/fpu/sched.h | 1 -
arch/x86/include/asm/fpu/types.h | 25 -------------------------
arch/x86/kernel/fpu/bugs.c | 4 ----
arch/x86/kernel/fpu/core.c | 13 +------------
arch/x86/kernel/fpu/init.c | 6 +-----
arch/x86/kernel/fpu/regset.c | 6 ------
arch/x86/kernel/fpu/signal.c | 15 ---------------
arch/x86/kernel/fpu/xstate.c | 5 -----
9 files changed, 4 insertions(+), 77 deletions(-)
diff --git a/arch/x86/include/asm/fpu/regset.h b/arch/x86/include/asm/fpu/regset.h
index 697b77e..4337209 100644
--- a/arch/x86/include/asm/fpu/regset.h
+++ b/arch/x86/include/asm/fpu/regset.h
@@ -9,10 +9,8 @@
extern user_regset_active_fn regset_fpregs_active, regset_xregset_fpregs_active,
ssp_active;
-extern user_regset_get2_fn fpregs_get, xfpregs_get, fpregs_soft_get,
- xstateregs_get, ssp_get;
-extern user_regset_set_fn fpregs_set, xfpregs_set, fpregs_soft_set,
- xstateregs_set, ssp_set;
+extern user_regset_get2_fn fpregs_get, xfpregs_get, xstateregs_get, ssp_get;
+extern user_regset_set_fn fpregs_set, xfpregs_set, xstateregs_set, ssp_set;
/*
* xstateregs_active == regset_fpregs_active. Please refer to the comment
diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 89004f4..48d7437 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -32,7 +32,6 @@ extern void fpu_flush_thread(void);
static inline void switch_fpu(struct task_struct *old, int cpu)
{
if (!test_tsk_thread_flag(old, TIF_NEED_FPU_LOAD) &&
- cpu_feature_enabled(X86_FEATURE_FPU) &&
!(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
struct fpu *old_fpu = x86_task_fpu(old);
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 93e99d2..ea02832 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -75,30 +75,6 @@ struct fxregs_state {
#define MXCSR_AND_FLAGS_SIZE sizeof(u64)
/*
- * Software based FPU emulation state. This is arbitrary really,
- * it matches the x87 format to make it easier to understand:
- */
-struct swregs_state {
- u32 cwd;
- u32 swd;
- u32 twd;
- u32 fip;
- u32 fcs;
- u32 foo;
- u32 fos;
- /* 8*10 bytes for each FP-reg = 80 bytes: */
- u32 st_space[20];
- u8 ftop;
- u8 changed;
- u8 lookahead;
- u8 no_update;
- u8 rm;
- u8 alimit;
- struct math_emu_info *info;
- u32 entry_eip;
-};
-
-/*
* List of XSAVE features Linux knows about:
*/
enum xfeature {
@@ -369,7 +345,6 @@ struct xregs_state {
union fpregs_state {
struct fregs_state fsave;
struct fxregs_state fxsave;
- struct swregs_state soft;
struct xregs_state xsave;
u8 __padding[PAGE_SIZE];
};
diff --git a/arch/x86/kernel/fpu/bugs.c b/arch/x86/kernel/fpu/bugs.c
index edbafc5..4b84cd0 100644
--- a/arch/x86/kernel/fpu/bugs.c
+++ b/arch/x86/kernel/fpu/bugs.c
@@ -29,10 +29,6 @@ void __init fpu__init_check_bugs(void)
{
s32 fdiv_bug;
- /* kernel_fpu_begin/end() relies on patched alternative instructions. */
- if (!boot_cpu_has(X86_FEATURE_FPU))
- return;
-
kernel_fpu_begin();
/*
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d1aeecd..67d4db3 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -491,7 +491,7 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
if (likely(kfpu_mask & KFPU_MXCSR) && boot_cpu_has(X86_FEATURE_XMM))
ldmxcsr(MXCSR_DEFAULT);
- if (unlikely(kfpu_mask & KFPU_387) && boot_cpu_has(X86_FEATURE_FPU))
+ if (unlikely(kfpu_mask & KFPU_387))
asm volatile ("fninit");
}
EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask);
@@ -672,9 +672,6 @@ int fpu_clone(struct task_struct *dst, u64 clone_flags, bool minimal,
fpstate_reset(dst_fpu);
- if (!cpu_feature_enabled(X86_FEATURE_FPU))
- return 0;
-
/*
* Enforce reload for user space tasks and prevent kernel threads
* from trying to save the FPU registers on context switch.
@@ -833,11 +830,6 @@ void fpu__clear_user_states(struct fpu *fpu)
WARN_ON_FPU(fpu != x86_task_fpu(current));
fpregs_lock();
- if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
- fpu_reset_fpstate_regs();
- fpregs_unlock();
- return;
- }
/*
* Ensure that current's supervisor states are loaded into their
@@ -874,9 +866,6 @@ void fpu_flush_thread(void)
*/
void switch_fpu_return(void)
{
- if (!cpu_feature_enabled(X86_FEATURE_FPU))
- return;
-
fpregs_restore_userregs();
}
EXPORT_SYMBOL_FOR_KVM(switch_fpu_return);
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 0d33c21..1a92ec4 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -31,8 +31,6 @@ static void fpu__init_cpu_generic(void)
cr0 = read_cr0();
cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
- if (!boot_cpu_has(X86_FEATURE_FPU))
- cr0 |= X86_CR0_EM;
write_cr0(cr0);
/* Flush out any pending x87 state: */
@@ -184,9 +182,7 @@ static void __init fpu__init_system_xstate_size_legacy(void)
* Note that the size configuration might be overwritten later
* during fpu__init_system_xstate().
*/
- if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
- size = sizeof(struct swregs_state);
- } else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
+ if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
size = sizeof(struct fxregs_state);
fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
} else {
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 0986c22..f96affd 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -407,9 +407,6 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset,
sync_fpstate(fpu);
- if (!cpu_feature_enabled(X86_FEATURE_FPU))
- return fpregs_soft_get(target, regset, to);
-
if (!cpu_feature_enabled(X86_FEATURE_FXSR)) {
return membuf_write(&to, &fpu->fpstate->regs.fsave,
sizeof(struct fregs_state));
@@ -441,9 +438,6 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
if (pos != 0 || count != sizeof(struct user_i387_ia32_struct))
return -EINVAL;
- if (!cpu_feature_enabled(X86_FEATURE_FPU))
- return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
-
ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
if (ret)
return ret;
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 594ba36..1f721ac 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -212,14 +212,6 @@ bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u
ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
IS_ENABLED(CONFIG_IA32_EMULATION));
- if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
- struct user_i387_ia32_struct fp;
-
- fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
- .left = sizeof(fp)});
- return !copy_to_user(buf, &fp, sizeof(fp));
- }
-
if (!access_ok(buf, size))
return false;
@@ -499,13 +491,6 @@ bool fpu__restore_sig(void __user *buf, int ia32_frame)
if (!access_ok(buf, size))
goto out;
- if (!IS_ENABLED(CONFIG_X86_64) && !cpu_feature_enabled(X86_FEATURE_FPU)) {
- success = !fpregs_soft_set(current, NULL, 0,
- sizeof(struct user_i387_ia32_struct),
- NULL, buf);
- goto out;
- }
-
if (use_xsave()) {
struct _fpx_sw_bytes fx_sw_user;
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index a2b6ede..561eec7 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -811,11 +811,6 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
int err;
int i;
- if (!boot_cpu_has(X86_FEATURE_FPU)) {
- pr_info("x86/fpu: No FPU detected\n");
- return;
- }
-
if (!boot_cpu_has(X86_FEATURE_XSAVE)) {
pr_info("x86/fpu: x87 FPU will use %s\n",
boot_cpu_has(X86_FEATURE_FXSR) ? "FXSAVE" : "FSAVE");