The code has the following problems: - it uses a single global 'fx_scratch' area that multiple CPUs could write into simultaneously, in theory.
- it wastes 512 bytes of .data for something that is only rarely used. Fix this by moving the state buffer to the stack. Note that while this is 512 bytes, we don't ever call this function in very deep callchains, so its stack usage should not be a problem. Also add comments to explain the magic 0x0000ffbf default value. Reviewed-by: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Fenghua Yu <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Thomas Gleixner <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/fpu/init.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index 33df056b1624..0b16f61cb2a4 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -68,18 +68,26 @@ void fpu__init_check_bugs(void) * Boot time FPU feature detection code: */ unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu; + unsigned int xstate_size; EXPORT_SYMBOL_GPL(xstate_size); -static struct i387_fxsave_struct fx_scratch; static void mxcsr_feature_mask_init(void) { - unsigned long mask = 0; + unsigned int mask = 0; if (cpu_has_fxsr) { - memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct)); - asm volatile("fxsave %0" : "+m" (fx_scratch)); - mask = fx_scratch.mxcsr_mask; + struct i387_fxsave_struct fx_tmp __aligned(32) = { }; + + asm volatile("fxsave %0" : "+m" (fx_tmp)); + + mask = fx_tmp.mxcsr_mask; + + /* + * If zero then use the default features mask, + * which has all features set, except the + * denormals-are-zero feature bit: + */ if (mask == 0) mask = 0x0000ffbf; } -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
