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author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-08-04 03:21:10 +0300 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-08-04 03:21:10 +0300 |
commit | 0a897743ac258927dd29bb91ac663b568f53429d (patch) | |
tree | c98ac1b01fe05dc48685fae3f8916ec6e7143cad /lib/test_fpu.c | |
parent | 335ad94c218e96ef12f56d93eadc884731aa23b1 (diff) | |
parent | 4185b3b92792eaec5869266e594338343421ffb0 (diff) | |
download | linux-0a897743ac258927dd29bb91ac663b568f53429d.tar.xz |
Merge tag 'x86-fpu-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 FPU selftest from Ingo Molnar:
"Add the /sys/kernel/debug/selftest_helpers/test_fpu FPU self-test"
* tag 'x86-fpu-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
selftests/fpu: Add an FPU selftest
Diffstat (limited to 'lib/test_fpu.c')
-rw-r--r-- | lib/test_fpu.c | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/lib/test_fpu.c b/lib/test_fpu.c new file mode 100644 index 000000000000..c33764aa3eb8 --- /dev/null +++ b/lib/test_fpu.c @@ -0,0 +1,89 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Test cases for using floating point operations inside a kernel module. + * + * This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially + * when userland has modified the floating point control registers. The kernel + * state might depend on the state set by the userland thread that was active + * before a syscall. + * + * To facilitate the test, this module registers file + * /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a + * sequence of floating point operations. If the operations fail, either the + * read returns error status or the kernel crashes. + * If the operations succeed, the read returns "1\n". + */ + +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/debugfs.h> +#include <asm/fpu/api.h> + +static int test_fpu(void) +{ + /* + * This sequence of operations tests that rounding mode is + * to nearest and that denormal numbers are supported. + * Volatile variables are used to avoid compiler optimizing + * the calculations away. + */ + volatile double a, b, c, d, e, f, g; + + a = 4.0; + b = 1e-15; + c = 1e-310; + + /* Sets precision flag */ + d = a + b; + + /* Result depends on rounding mode */ + e = a + b / 2; + + /* Denormal and very large values */ + f = b / c; + + /* Depends on denormal support */ + g = a + c * f; + + if (d > a && e > a && g > a) + return 0; + else + return -EINVAL; +} + +static int test_fpu_get(void *data, u64 *val) +{ + int status = -EINVAL; + + kernel_fpu_begin(); + status = test_fpu(); + kernel_fpu_end(); + + *val = 1; + return status; +} + +DEFINE_SIMPLE_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n"); +static struct dentry *selftest_dir; + +static int __init test_fpu_init(void) +{ + selftest_dir = debugfs_create_dir("selftest_helpers", NULL); + if (!selftest_dir) + return -ENOMEM; + + debugfs_create_file("test_fpu", 0444, selftest_dir, NULL, + &test_fpu_fops); + + return 0; +} + +static void __exit test_fpu_exit(void) +{ + debugfs_remove(selftest_dir); +} + +module_init(test_fpu_init); +module_exit(test_fpu_exit); + +MODULE_LICENSE("GPL"); |