#include <linux/sched.h>
#include <linux/init.h>
-/*
- * Initialize the TS bit in CR0 according to the style of context-switches
- * we are using:
- */
-static void fpu__init_cpu_ctx_switch(void)
-{
- if (!boot_cpu_has(X86_FEATURE_EAGER_FPU))
- stts();
- else
- clts();
-}
-
/*
* Initialize the registers found in all CPUs, CR0 and CR4:
*/
{
fpu__init_cpu_generic();
fpu__init_cpu_xstate();
- fpu__init_cpu_ctx_switch();
}
-/*
- * The earliest FPU detection code.
- *
- * Set the X86_FEATURE_FPU CPU-capability bit based on
- * trying to execute an actual sequence of FPU instructions:
- */
-static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
+static bool fpu__probe_without_cpuid(void)
{
unsigned long cr0;
u16 fsw, fcw;
cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
write_cr0(cr0);
- if (!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
- asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
- : "+m" (fsw), "+m" (fcw));
+ asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
+
+ pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
- if (fsw == 0 && (fcw & 0x103f) == 0x003f)
- set_cpu_cap(c, X86_FEATURE_FPU);
+ return fsw == 0 && (fcw & 0x103f) == 0x003f;
+}
+
+static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
+{
+ if (!boot_cpu_has(X86_FEATURE_CPUID) &&
+ !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
+ if (fpu__probe_without_cpuid())
+ setup_force_cpu_cap(X86_FEATURE_FPU);
else
- clear_cpu_cap(c, X86_FEATURE_FPU);
+ setup_clear_cpu_cap(X86_FEATURE_FPU);
}
#ifndef CONFIG_MATH_EMULATION
- if (!boot_cpu_has(X86_FEATURE_FPU)) {
+ 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");
fpu_user_xstate_size = fpu_kernel_xstate_size;
}
-/*
- * FPU context switching strategies:
- *
- * Against popular belief, we don't do lazy FPU saves, due to the
- * task migration complications it brings on SMP - we only do
- * lazy FPU restores.
- *
- * 'lazy' is the traditional strategy, which is based on setting
- * CR0::TS to 1 during context-switch (instead of doing a full
- * restore of the FPU state), which causes the first FPU instruction
- * after the context switch (whenever it is executed) to fault - at
- * which point we lazily restore the FPU state into FPU registers.
- *
- * Tasks are of course under no obligation to execute FPU instructions,
- * so it can easily happen that another context-switch occurs without
- * a single FPU instruction being executed. If we eventually switch
- * back to the original task (that still owns the FPU) then we have
- * not only saved the restores along the way, but we also have the
- * FPU ready to be used for the original task.
- *
- * 'lazy' is deprecated because it's almost never a performance win
- * and it's much more complicated than 'eager'.
- *
- * 'eager' switching is by default on all CPUs, there we switch the FPU
- * state during every context switch, regardless of whether the task
- * has used FPU instructions in that time slice or not. This is done
- * because modern FPU context saving instructions are able to optimize
- * state saving and restoration in hardware: they can detect both
- * unused and untouched FPU state and optimize accordingly.
- *
- * [ Note that even in 'lazy' mode we might optimize context switches
- * to use 'eager' restores, if we detect that a task is using the FPU
- * frequently. See the fpu->counter logic in fpu/internal.h for that. ]
- */
-static enum { ENABLE, DISABLE } eagerfpu = ENABLE;
-
/*
* Find supported xfeatures based on cpu features and command-line input.
* This must be called after fpu__init_parse_early_param() is called and
*/
u64 __init fpu__get_supported_xfeatures_mask(void)
{
- /* Support all xfeatures known to us */
- if (eagerfpu != DISABLE)
- return XCNTXT_MASK;
-
- /* Warning of xfeatures being disabled for no eagerfpu mode */
- if (xfeatures_mask & XFEATURE_MASK_EAGER) {
- pr_err("x86/fpu: eagerfpu switching disabled, disabling the following xstate features: 0x%llx.\n",
- xfeatures_mask & XFEATURE_MASK_EAGER);
- }
-
- /* Return a mask that masks out all features requiring eagerfpu mode */
- return ~XFEATURE_MASK_EAGER;
+ return XCNTXT_MASK;
}
-/*
- * Disable features dependent on eagerfpu.
- */
-static void __init fpu__clear_eager_fpu_features(void)
-{
- setup_clear_cpu_cap(X86_FEATURE_MPX);
-}
-
-/*
- * Pick the FPU context switching strategy:
- *
- * When eagerfpu is AUTO or ENABLE, we ensure it is ENABLE if either of
- * the following is true:
- *
- * (1) the cpu has xsaveopt, as it has the optimization and doing eager
- * FPU switching has a relatively low cost compared to a plain xsave;
- * (2) the cpu has xsave features (e.g. MPX) that depend on eager FPU
- * switching. Should the kernel boot with noxsaveopt, we support MPX
- * with eager FPU switching at a higher cost.
- */
+/* Legacy code to initialize eager fpu mode. */
static void __init fpu__init_system_ctx_switch(void)
{
static bool on_boot_cpu __initdata = 1;
on_boot_cpu = 0;
WARN_ON_FPU(current->thread.fpu.fpstate_active);
- current_thread_info()->status = 0;
-
- if (boot_cpu_has(X86_FEATURE_XSAVEOPT) && eagerfpu != DISABLE)
- eagerfpu = ENABLE;
-
- if (xfeatures_mask & XFEATURE_MASK_EAGER)
- eagerfpu = ENABLE;
-
- if (eagerfpu == ENABLE)
- setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
-
- printk(KERN_INFO "x86/fpu: Using '%s' FPU context switches.\n", eagerfpu == ENABLE ? "eager" : "lazy");
}
/*
*/
static void __init fpu__init_parse_early_param(void)
{
- if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off")) {
- eagerfpu = DISABLE;
- fpu__clear_eager_fpu_features();
- }
-
if (cmdline_find_option_bool(boot_command_line, "no387"))
setup_clear_cpu_cap(X86_FEATURE_FPU);
*/
fpu__init_cpu();
- /*
- * But don't leave CR0::TS set yet, as some of the FPU setup
- * methods depend on being able to execute FPU instructions
- * that will fault on a set TS, such as the FXSAVE in
- * fpu__init_system_mxcsr().
- */
- clts();
-
fpu__init_system_generic();
fpu__init_system_xstate_size_legacy();
fpu__init_system_xstate();
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