[RFC PATCH 54/73] x86/pvm: Detect PVM hypervisor support

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Detect PVM hypervisor support through the use of the PVM synthetic
instruction 'PVM_SYNTHETIC_CPUID'. This is a necessary step in preparing
to initialize the PVM guest during booting.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
 arch/x86/include/asm/pvm_para.h | 69 +++++++++++++++++++++++++++++++++
 arch/x86/kernel/Makefile        |  1 +
 arch/x86/kernel/pvm.c           | 22 +++++++++++
 3 files changed, 92 insertions(+)
 create mode 100644 arch/x86/include/asm/pvm_para.h
 create mode 100644 arch/x86/kernel/pvm.c

diff --git a/arch/x86/include/asm/pvm_para.h b/arch/x86/include/asm/pvm_para.h
new file mode 100644
index 000000000000..efd7afdf9be9
--- /dev/null
+++ b/arch/x86/include/asm/pvm_para.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_PVM_PARA_H
+#define _ASM_X86_PVM_PARA_H
+
+#include <linux/init.h>
+#include <uapi/asm/pvm_para.h>
+
+#ifdef CONFIG_PVM_GUEST
+#include <asm/irqflags.h>
+#include <uapi/asm/kvm_para.h>
+
+void __init pvm_early_setup(void);
+
+static inline void pvm_cpuid(unsigned int *eax, unsigned int *ebx,
+			     unsigned int *ecx, unsigned int *edx)
+{
+	asm(__ASM_FORM(.byte PVM_SYNTHETIC_CPUID ;)
+		: "=a" (*eax),
+		  "=b" (*ebx),
+		  "=c" (*ecx),
+		  "=d" (*edx)
+		: "0" (*eax), "2" (*ecx));
+}
+
+/*
+ * pvm_detect() is called before event handling is set up and it might be
+ * possibly called under any hypervisor other than PVM, so it should not
+ * trigger any trap in all possible scenarios. PVM_SYNTHETIC_CPUID is supposed
+ * to not trigger any trap in the real or virtual x86 kernel mode and is also
+ * guaranteed to trigger a trap in the underlying hardware user mode for the
+ * hypervisor emulating it.
+ */
+static inline bool pvm_detect(void)
+{
+	unsigned long cs;
+	uint32_t eax, signature[3];
+
+	/* check underlying interrupt flags */
+	if (arch_irqs_disabled_flags(native_save_fl()))
+		return false;
+
+	/* check underlying CS */
+	asm volatile("mov %%cs,%0\n\t" : "=r" (cs) : );
+	if ((cs & 3) != 3)
+		return false;
+
+	/* check KVM_SIGNATURE and KVM_CPUID_VENDOR_FEATURES */
+	eax = KVM_CPUID_SIGNATURE;
+	pvm_cpuid(&eax, &signature[0], &signature[1], &signature[2]);
+	if (memcmp(KVM_SIGNATURE, signature, 12))
+		return false;
+	if (eax < KVM_CPUID_VENDOR_FEATURES)
+		return false;
+
+	/* check PVM_CPUID_SIGNATURE */
+	eax = KVM_CPUID_VENDOR_FEATURES;
+	pvm_cpuid(&eax, &signature[0], &signature[1], &signature[2]);
+	if (signature[0] != PVM_CPUID_SIGNATURE)
+		return false;
+
+	return true;
+}
+#else
+static inline void pvm_early_setup(void)
+{
+}
+#endif /* CONFIG_PVM_GUEST */
+
+#endif /* _ASM_X86_PVM_PARA_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index dc1f5a303e9b..67f11f7d5c88 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -129,6 +129,7 @@ obj-$(CONFIG_AMD_NB)		+= amd_nb.o
 obj-$(CONFIG_DEBUG_NMI_SELFTEST) += nmi_selftest.o
 
 obj-$(CONFIG_KVM_GUEST)		+= kvm.o kvmclock.o
+obj-$(CONFIG_PVM_GUEST)		+= pvm.o
 obj-$(CONFIG_PARAVIRT)		+= paravirt.o
 obj-$(CONFIG_PARAVIRT_SPINLOCKS)+= paravirt-spinlocks.o
 obj-$(CONFIG_PARAVIRT_CLOCK)	+= pvclock.o
diff --git a/arch/x86/kernel/pvm.c b/arch/x86/kernel/pvm.c
new file mode 100644
index 000000000000..2d27044eaf25
--- /dev/null
+++ b/arch/x86/kernel/pvm.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * KVM PVM paravirt_ops implementation
+ *
+ * Copyright (C) 2020 Ant Group
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+#define pr_fmt(fmt) "pvm-guest: " fmt
+
+#include <asm/cpufeature.h>
+#include <asm/pvm_para.h>
+
+void __init pvm_early_setup(void)
+{
+	if (!pvm_detect())
+		return;
+
+	setup_force_cpu_cap(X86_FEATURE_KVM_PVM_GUEST);
+}
-- 
2.19.1.6.gb485710b