kvm: RDTSCP on AMD

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From	Borislav Petkov <bp@alien8.de>
Newsgroups	linux.kernel
Subject	kvm: RDTSCP on AMD
Date	Wed, 06 Jul 2016 14:50:02 +0200
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Hi guys,

how about this below to enable RDTSCP emulation on AMD? IOW, I'm staring
at

  33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models")

in the qemu repo.

It seems to work here, RDTSCP in the guest gives me node and cpu as
vsyscall_set_cpu() in the guest kernel has set them.

Thoughts?

(Below is the simple qemu diff reenabling RDTSCP)

---
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 16ef31b87452..5a238f5402f5 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1131,6 +1131,7 @@ static void init_vmcb(struct vcpu_svm *svm)
 	set_intercept(svm, INTERCEPT_STGI);
 	set_intercept(svm, INTERCEPT_CLGI);
 	set_intercept(svm, INTERCEPT_SKINIT);
+	set_intercept(svm, INTERCEPT_RDTSCP);
 	set_intercept(svm, INTERCEPT_WBINVD);
 	set_intercept(svm, INTERCEPT_MONITOR);
 	set_intercept(svm, INTERCEPT_MWAIT);
@@ -3009,6 +3010,20 @@ static int skinit_interception(struct vcpu_svm *svm)
 	return 1;
 }
 
+static int rdtscp_interception(struct vcpu_svm *svm)
+{
+	u64 tsc;
+
+	tsc = kvm_scale_tsc(&svm->vcpu, rdtsc()) + svm->vmcb->control.tsc_offset;
+
+	kvm_register_write(&svm->vcpu, VCPU_REGS_RAX, tsc & 0xffffffff);
+	kvm_register_write(&svm->vcpu, VCPU_REGS_RDX, tsc >> 32);
+	kvm_register_write(&svm->vcpu, VCPU_REGS_RCX, svm->tsc_aux);
+
+	skip_emulated_instruction(&svm->vcpu);
+	return 1;
+}
+
 static int wbinvd_interception(struct vcpu_svm *svm)
 {
 	kvm_emulate_wbinvd(&svm->vcpu);
@@ -3919,6 +3935,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
 	[SVM_EXIT_STGI]				= stgi_interception,
 	[SVM_EXIT_CLGI]				= clgi_interception,
 	[SVM_EXIT_SKINIT]			= skinit_interception,
+	[SVM_EXIT_RDTSCP]			= rdtscp_interception,
 	[SVM_EXIT_WBINVD]                       = wbinvd_interception,
 	[SVM_EXIT_MONITOR]			= monitor_interception,
 	[SVM_EXIT_MWAIT]			= mwait_interception,
---

qemu diff:

---
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 3bd3cfc3ad16..aa6d0d027d00 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -1332,9 +1332,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_FXSR |
+            CPUID_EXT2_LM | CPUID_EXT2_FXSR | CPUID_EXT2_RDTSCP |
             CPUID_EXT2_MMX | CPUID_EXT2_NX | CPUID_EXT2_PSE36 |
             CPUID_EXT2_PAT | CPUID_EXT2_CMOV | CPUID_EXT2_MCA |
             CPUID_EXT2_PGE | CPUID_EXT2_MTRR | CPUID_EXT2_SYSCALL |
@@ -1362,9 +1361,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_FXSR |
+            CPUID_EXT2_LM | CPUID_EXT2_FXSR | CPUID_EXT2_RDTSCP |
             CPUID_EXT2_MMX | CPUID_EXT2_NX | CPUID_EXT2_PSE36 |
             CPUID_EXT2_PAT | CPUID_EXT2_CMOV | CPUID_EXT2_MCA |
             CPUID_EXT2_PGE | CPUID_EXT2_MTRR | CPUID_EXT2_SYSCALL |
@@ -1395,9 +1393,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM |
+            CPUID_EXT2_LM | CPUID_EXT2_RDTSCP |
             CPUID_EXT2_PDPE1GB | CPUID_EXT2_FXSR | CPUID_EXT2_MMX |
             CPUID_EXT2_NX | CPUID_EXT2_PSE36 | CPUID_EXT2_PAT |
             CPUID_EXT2_CMOV | CPUID_EXT2_MCA | CPUID_EXT2_PGE |
@@ -1431,9 +1428,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM |
+            CPUID_EXT2_LM | CPUID_EXT2_RDTSCP |
             CPUID_EXT2_PDPE1GB | CPUID_EXT2_FXSR | CPUID_EXT2_MMX |
             CPUID_EXT2_NX | CPUID_EXT2_PSE36 | CPUID_EXT2_PAT |
             CPUID_EXT2_CMOV | CPUID_EXT2_MCA | CPUID_EXT2_PGE |




-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

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Thread

kvm: RDTSCP on AMD Borislav Petkov <bp@alien8.de> - 2016-07-06 14:50 +0200
  Re: kvm: RDTSCP on AMD Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 15:10 +0200
    Re: kvm: RDTSCP on AMD Eduardo Habkost <ehabkost@redhat.com> - 2016-07-06 19:40 +0200
      Re: kvm: RDTSCP on AMD Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 23:30 +0200

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