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Subject[PATCH 2/2] KVM: VMX: Add Force Emulation Prefix for "emulate the next instruction"
Date
From: Wanpeng Li <wanpengli@tencent.com>

This patch introduces a Force Emulation Prefix (ud2a; .ascii "kvm") for
"emulate the next instruction", the codes will be executed by emulator
instead of processor, for testing purposes.

A testcase here:

#include <stdio.h>
#include <string.h>

#define HYPERVISOR_INFO 0x40000000

#define CPUID(idx, eax, ebx, ecx, edx)\
asm volatile (\
"ud2a; .ascii \"kvm\"; 1: cpuid" \
:"=b" (*ebx), "=a" (*eax),"=c" (*ecx), "=d" (*edx)\
:"0"(idx) );

void main()
{
unsigned int eax,ebx,ecx,edx;
char string[13];

CPUID(HYPERVISOR_INFO, &eax, &ebx, &ecx, &edx);
*(unsigned int *)(string+0) = ebx;
*(unsigned int *)(string+4) = ecx;
*(unsigned int *)(string+8) = edx;

string[12] = 0;
if (strncmp(string, "KVMKVMKVM\0\0\0",12) == 0)
printf("kvm guest\n");
else
printf("bare hardware\n");
}

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/vmx.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0f99833..90abed8 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -108,6 +108,9 @@ module_param_named(enable_shadow_vmcs, enable_shadow_vmcs, bool, S_IRUGO);
static bool __read_mostly nested = 0;
module_param(nested, bool, S_IRUGO);

+static bool __read_mostly fep = 0;
+module_param(fep, bool, S_IRUGO);
+
static u64 __read_mostly host_xss;

static bool __read_mostly enable_pml = 1;
@@ -6218,8 +6221,21 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
static int handle_ud(struct kvm_vcpu *vcpu)
{
enum emulation_result er;
+ int emulation_type = EMULTYPE_TRAP_UD;
+
+ if (fep) {
+ char sig[5]; /* ud2; .ascii "kvm" */
+ struct x86_exception e;
+
+ kvm_read_guest_virt(&vcpu->arch.emulate_ctxt,
+ kvm_get_linear_rip(vcpu), sig, sizeof(sig), &e);
+ if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) {
+ emulation_type = 0;
+ kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
+ }
+ }

- er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
+ er = emulate_instruction(vcpu, emulation_type);
if (er == EMULATE_USER_EXIT)
return 0;
if (er != EMULATE_DONE)
--
2.7.4
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