From e45122893a9870813f9bd7b4add4f613e6f29008 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 20 Jan 2021 21:09:48 -0800 Subject: x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Currently, requesting kernel FPU access doesn't distinguish which parts of the extended ("FPU") state are needed. This is nice for simplicity, but there are a few cases in which it's suboptimal: - The vast majority of in-kernel FPU users want XMM/YMM/ZMM state but do not use legacy 387 state. These users want MXCSR initialized but don't care about the FPU control word. Skipping FNINIT would save time. (Empirically, FNINIT is several times slower than LDMXCSR.) - Code that wants MMX doesn't want or need MXCSR initialized. _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and initializing MXCSR will fail because LDMXCSR generates an #UD when the aforementioned CR4 bit is not set. - Any future in-kernel users of XFD (eXtended Feature Disable)-capable dynamic states will need special handling. Add a more specific API that allows callers to specify exactly what they want. Signed-off-by: Andy Lutomirski Signed-off-by: Borislav Petkov Tested-by: Krzysztof Piotr Olędzki Link: https://lkml.kernel.org/r/aff1cac8b8fc7ee900cf73e8f2369966621b053f.1611205691.git.luto@kernel.org --- arch/x86/kernel/fpu/core.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'arch/x86/kernel/fpu') diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index eb86a2b831b1..571220ac8bea 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -121,7 +121,7 @@ int copy_fpregs_to_fpstate(struct fpu *fpu) } EXPORT_SYMBOL(copy_fpregs_to_fpstate); -void kernel_fpu_begin(void) +void kernel_fpu_begin_mask(unsigned int kfpu_mask) { preempt_disable(); @@ -141,13 +141,14 @@ void kernel_fpu_begin(void) } __cpu_invalidate_fpregs_state(); - if (boot_cpu_has(X86_FEATURE_XMM)) + /* Put sane initial values into the control registers. */ + if (likely(kfpu_mask & KFPU_MXCSR) && boot_cpu_has(X86_FEATURE_XMM)) ldmxcsr(MXCSR_DEFAULT); - if (boot_cpu_has(X86_FEATURE_FPU)) + if (unlikely(kfpu_mask & KFPU_387) && boot_cpu_has(X86_FEATURE_FPU)) asm volatile ("fninit"); } -EXPORT_SYMBOL_GPL(kernel_fpu_begin); +EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask); void kernel_fpu_end(void) { -- cgit v1.2.3