From: Dave Hansen <[email protected]> I don't think it is really possible to have a system where CPUID enumerates support for XSAVE but that it does not have FP/SSE (they are "legacy" features and always present).
But, I did manage to hit this case in qemu when I enabled its somewhat shaky XSAVE support. The bummer is that the FPU is set up before we parse the command-line or have *any* console support including earlyprintk. That turned what should have been an easy thing to debug in to a bit more of an odyssey. So a BUG() here is worthless. All it does it guarantee that if/when we hit this case we have an empty console. So, remove the BUG() and try to limp along by disabling XSAVE and trying to continue. Add a comment on why we are doing this, and also add a common "out_disable" path for leaving fpu__init_system_xstate(). Signed-off-by: Dave Hansen <[email protected]> --- b/arch/x86/kernel/fpu/xstate.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff -puN arch/x86/kernel/fpu/xstate.c~x86-fpu-do-not-BUG_ON-early arch/x86/kernel/fpu/xstate.c --- a/arch/x86/kernel/fpu/xstate.c~x86-fpu-do-not-BUG_ON-early 2016-07-20 12:11:42.226323250 -0700 +++ b/arch/x86/kernel/fpu/xstate.c 2016-07-20 12:29:49.574991502 -0700 @@ -714,8 +714,13 @@ void __init fpu__init_system_xstate(void xfeatures_mask = eax + ((u64)edx << 32); if ((xfeatures_mask & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) { + /* + * This indicates that something really unexpected happened + * with the enumeration. Disable XSAVE and try to continue + * booting without it. This is too early to BUG(). + */ pr_err("x86/fpu: FP/SSE not present amongst the CPU's xstate features: 0x%llx.\n", xfeatures_mask); - BUG(); + goto out_disable; } xfeatures_mask &= fpu__get_supported_xfeatures_mask(); @@ -723,11 +728,8 @@ void __init fpu__init_system_xstate(void /* Enable xstate instructions to be able to continue with initialization: */ fpu__init_cpu_xstate(); err = init_xstate_size(); - if (err) { - /* something went wrong, boot without any XSAVE support */ - fpu__init_disable_system_xstate(); - return; - } + if (err) + goto out_disable; /* * Update info used for ptrace frames; use standard-format size and no @@ -744,6 +746,11 @@ void __init fpu__init_system_xstate(void xfeatures_mask, fpu_kernel_xstate_size, boot_cpu_has(X86_FEATURE_XSAVES) ? "compacted" : "standard"); + return; + +out_disable: + /* something went wrong, try to boot without any XSAVE support */ + fpu__init_disable_system_xstate(); } /* _
