Commit-ID: b1276c48e91bee869454301d3678cc49d8f57ab4
Gitweb: http://git.kernel.org/tip/b1276c48e91bee869454301d3678cc49d8f57ab4
Author: Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Wed, 29 Apr 2015 10:58:03 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 19 May 2015 15:48:02 +0200
x86/fpu: Initialize fpregs in fpu__init_cpu_generic()
FPU fpregs do not get initialized during bootup on secondary CPUs,
on non-xsave capable CPUs.
For example on one of my systems, the secondary CPU has this FPU
state on bootup:
x86: Booting SMP configuration:
.... node #0, CPUs: #1
x86/fpu ######################
x86/fpu # FPU register dump on CPU#1:
x86/fpu # ... CWD: ffff0040
x86/fpu # ... SWD: ffff0000
x86/fpu # ... TWD: ffff555a
x86/fpu # ... FIP: 00000000
x86/fpu # ... FCS: 00000000
x86/fpu # ... FOO: 00000000
x86/fpu # ... FOS: ffff0000
x86/fpu # ... FP0: 02 57 00 00 00 00 00 00 ff ff
x86/fpu # ... FP1: 1b e2 00 00 00 00 00 00 ff ff
x86/fpu # ... FP2: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... FP3: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... FP4: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... FP5: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... FP6: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... FP7: 00 00 00 00 00 00 00 00 00 00
x86/fpu # ... SW: dadadada
x86/fpu ######################
Note how CWD and TWD are off their usual init state (0x037f and 0xffff),
and how FP0 and FP1 has non-zero content.
This is normally not a problem, because any user-space FPU state
is initalized properly - but it can complicate the use of FPU
instructions in kernel code via kernel_fpu_begin()/end(): if
the FPU using code does not initialize registers itself, it
might generate spurious exceptions depending on which CPU it
executes on.
Fix this by initializing the x87 state via the FNINIT instruction.
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/fpu/init.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 460e7e2..72219ce 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -36,6 +36,9 @@ static void fpu__init_cpu_generic(void)
if (!cpu_has_fpu)
cr0 |= X86_CR0_EM;
write_cr0(cr0);
+
+ /* Flush out any pending x87 state: */
+ asm volatile ("fninit");
}
/*
--
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