x86/fpu: Fix eager-FPU handling on legacy FPU machines

bp3tk0v · Ingo Molnar · commit 6e6867093de3 · 2016-03-12T16:13:55.000+01:00
i486 derived cores like Intel Quark support only the very old, legacy x87 FPU (FSAVE/FRSTOR, CPUID bit FXSR is not set), and our FPU code wasn't handling the saving and restoring there properly in the 'eagerfpu' case. So after we made eagerfpu the default for all CPU types: 58122bf x86/fpu: Default eagerfpu=on on all CPUs these old FPU designs broke. First, Andy Shevchenko reported a splat: WARNING: CPU: 0 PID: 823 at arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160 which was us trying to execute FXRSTOR on those machines even though they don't support it. After taking care of that, Bryan O'Donoghue reported that a simple FPU test still failed because we weren't initializing the FPU state properly on those machines. Take care of all that. Reported-and-tested-by: Bryan O'Donoghue <pure.logic@nexus-software.ie> Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yu-cheng <yu-cheng.yu@intel.com> Link: http://lkml.kernel.org/r/20160311113206.GD4312@pd.tnic Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
@@ -409,8 +409,10 @@ static inline void copy_init_fpstate_to_fpregs(void)
 {
 	if (use_xsave())
 		copy_kernel_to_xregs(&init_fpstate.xsave, -1);
-	else
+	else if (static_cpu_has(X86_FEATURE_FXSR))
 		copy_kernel_to_fxregs(&init_fpstate.fxsave);
+	else
+		copy_kernel_to_fregs(&init_fpstate.fsave);
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
@@ -134,7 +134,7 @@ static void __init fpu__init_system_generic(void)
 	 * Set up the legacy init FPU context. (xstate init might overwrite this
 	 * with a more modern format, if the CPU supports it.)
 	 */
-	fpstate_init_fxstate(&init_fpstate.fxsave);
+	fpstate_init(&init_fpstate);
 
 	fpu__init_system_mxcsr();
 }

Original file line number	Diff line number	Diff line change
`@@ -409,8 +409,10 @@ static inline void copy_init_fpstate_to_fpregs(void)`
`409`	`409`	`{`
`410`	`410`	`if (use_xsave())`
`411`	`411`	`copy_kernel_to_xregs(&init_fpstate.xsave, -1);`
`412`		`- else`
	`412`	`+ else if (static_cpu_has(X86_FEATURE_FXSR))`
`413`	`413`	`copy_kernel_to_fxregs(&init_fpstate.fxsave);`
	`414`	`+ else`
	`415`	`+ copy_kernel_to_fregs(&init_fpstate.fsave);`
`414`	`416`	`}`
`415`	`417`
`416`	`418`	`/*`
Original file line number	Diff line number	Diff line change
`@@ -134,7 +134,7 @@ static void __init fpu__init_system_generic(void)`
`134`	`134`	`* Set up the legacy init FPU context. (xstate init might overwrite this`
`135`	`135`	`* with a more modern format, if the CPU supports it.)`
`136`	`136`	`*/`
`137`		`- fpstate_init_fxstate(&init_fpstate.fxsave);`
	`137`	`+ fpstate_init(&init_fpstate);`
`138`	`138`
`139`	`139`	`fpu__init_system_mxcsr();`
`140`	`140`	`}`