Commit-ID: ec3ed4a2104b8d1ab8da2db5b1221b2ba8a7a6e1
Gitweb: http://git.kernel.org/tip/ec3ed4a2104b8d1ab8da2db5b1221b2ba8a7a6e1
Author: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate: Wed, 20 Jul 2016 12:45:51 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 21 Jul 2016 18:18:45 +0200
x86/fpu: Do not BUG_ON() in early FPU code
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 <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20160720194551.63BB2B58@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/fpu/xstate.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 3169bca..680049a 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -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();
}
/*
--
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