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Subject[tip:x86/xsave] x86, xsave: Make xstate_enable_boot_cpu() __init, protect on CPU 0
Commit-ID:  1cff92d8fdb27684308864d9cdb324bee43b40ab
Gitweb: http://git.kernel.org/tip/1cff92d8fdb27684308864d9cdb324bee43b40ab
Author: H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Wed, 21 Jul 2010 14:23:10 -0700
Committer: H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Wed, 21 Jul 2010 15:33:54 -0700

x86, xsave: Make xstate_enable_boot_cpu() __init, protect on CPU 0

xstate_enable_boot_cpu() is, as the name implies, only used on the
boot CPU; furthermore, it invokes alloc_bootmem(), which is __init;
hence it needs to be tagged __init rather than __cpuinit.

Furthermore, it is *not* safe in the long run to rely on CPU 0 only
coming online during the early boot -- at some point we're going to
support offlining (and re-onlining) the boot CPU, and at that point we
must not call xstate_enable_boot_cpu() again.

The code is a fair bit more obscure than one would like, because the
__ref overrides aren't quite powerful enough.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Robert Richter <robert.richter@amd.com>
LKML-Reference: <4C476236.1020302@zytor.com>
---
arch/x86/kernel/xsave.c | 28 +++++++++++++++++-----------
1 files changed, 17 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index cfc7901..b2549c3 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -360,10 +360,10 @@ unsigned int sig_xstate_size = sizeof(struct _fpstate);
/*
* Enable the extended processor state save/restore feature
*/
-static inline void xstate_enable(u64 mask)
+static inline void xstate_enable(void)
{
set_in_cr4(X86_CR4_OSXSAVE);
- xsetbv(XCR_XFEATURE_ENABLED_MASK, mask);
+ xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
}

/*
@@ -421,7 +421,7 @@ static void __init setup_xstate_init(void)
/*
* Enable and initialize the xsave feature.
*/
-static void __cpuinit xstate_enable_boot_cpu(void)
+static void __init xstate_enable_boot_cpu(void)
{
unsigned int eax, ebx, ecx, edx;

@@ -444,7 +444,7 @@ static void __cpuinit xstate_enable_boot_cpu(void)
*/
pcntxt_mask = pcntxt_mask & XCNTXT_MASK;

- xstate_enable(pcntxt_mask);
+ xstate_enable();

/*
* Recompute the context size for enabled features
@@ -462,16 +462,22 @@ static void __cpuinit xstate_enable_boot_cpu(void)
pcntxt_mask, xstate_size);
}

+/*
+ * For the very first instance, this calls xstate_enable_boot_cpu();
+ * for all subsequent instances, this calls xstate_enable().
+ *
+ * This is somewhat obfuscated due to the lack of powerful enough
+ * overrides for the section checks.
+ */
void __cpuinit xsave_init(void)
{
+ static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
+ void (*this_func)(void);
+
if (!cpu_has_xsave)
return;

- /*
- * Boot processor to setup the FP and extended state context info.
- */
- if (!smp_processor_id())
- xstate_enable_boot_cpu();
- else
- xstate_enable(pcntxt_mask);
+ this_func = next_func;
+ next_func = xstate_enable;
+ this_func();
}

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