[tip:x86/paravirt] x86: Introduce hypervisor_cpuid_base()

[tip-bot for Jason Wang]

Commit-ID:  96e39ac0e9d18020c8c5a41b64b8fe86c26575ab
Gitweb:     http://git.kernel.org/tip/96e39ac0e9d18020c8c5a41b64b8fe86c26575ab
Author:     Jason Wang <jasowang@xxxxxxxxxx>
AuthorDate: Thu, 25 Jul 2013 16:54:32 +0800
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Mon, 5 Aug 2013 06:33:54 -0700

x86: Introduce hypervisor_cpuid_base()

This patch introduce hypervisor_cpuid_base() which loop test the hypervisor
existence function until the signature match and check the number of leaves if
required. This could be used by Xen/KVM guest to detect the existence of
hypervisor.

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1374742475-2485-1-git-send-email-jasowang@xxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/processor.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 24cf5ae..7763307 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -971,6 +971,21 @@ unsigned long calc_aperfmperf_ratio(struct aperfmperf *old,
 	return ratio;
 }
 
+static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)
+{
+	uint32_t base, eax, signature[3];
+
+	for (base = 0x40000000; base < 0x40010000; base += 0x100) {
+		cpuid(base, &eax, &signature[0], &signature[1], &signature[2]);
+
+		if (!memcmp(sig, signature, 12) &&
+		    (leaves == 0 || ((eax - base) >= leaves)))
+			return base;
+	}
+
+	return 0;
+}
+
 extern unsigned long arch_align_stack(unsigned long sp);
 extern void free_init_pages(char *what, unsigned long begin, unsigned long end);
 
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