Not working anymore with kernel 6.5

[scoony]

I was trying to make a script to compile automatically the kernel for my gaming VM but now with the new kernels the compilation failed.

Something has probably changed in the svm.h file.

I've got a compilation error everytime I try to patch the files.

Anyone got a solution?

[Samuil1337]

I assume your are on AMD, so you can copy and paste everything like explained in the README, but append "svm_" to the method that is returned from the function you paste in. Basically you write a new patch that works with the changed code.

[YungBinary]

@scoony If you’re on Intel, I forked this repo and updated the patch for Linux kernel 6.8.0-45 (latest for Ubuntu). See my repo here -> https://github.com/YungBinary/RDTSC-KVM-Handler-v2

[scoony]

@scoony If you’re on Intel, I forked this repo and updated the patch for Linux kernel 6.8.0-45 (latest for Ubuntu). See my repo here -> https://github.com/YungBinary/RDTSC-KVM-Handler-v2

Hi @YungBinary , i'm on AMD, i gave up :(

[Samuil1337]

What, why? On amd the code literally works but you have to add it manually. Again, the only thing that changed is the kvm_skip_emulated_instruction function call. You have to prepend "svm_" and it will work. Although a heads-up, this isn't really a good implementation

[Username404-59]

Patch for AMD (no idea if it works, haven't tested it yet)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9df3e1e5ae81..a91aa30f498e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1292,6 +1292,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	svm_set_intercept(svm, INTERCEPT_XSETBV);
 	svm_set_intercept(svm, INTERCEPT_RDPRU);
 	svm_set_intercept(svm, INTERCEPT_RSM);
+	svm_set_intercept(svm, INTERCEPT_RDTSC);
 
 	if (!kvm_mwait_in_guest(vcpu->kvm)) {
 		svm_set_intercept(svm, INTERCEPT_MONITOR);
@@ -3286,6 +3287,42 @@ static int invpcid_interception(struct kvm_vcpu *vcpu)
 	return kvm_handle_invpcid(vcpu, type, gva);
 }
 
+static u32 print_once = 1;
+
+static int handle_rdtsc_interception(struct kvm_vcpu *vcpu) 
+{
+	static u64 rdtsc_fake = 0;
+	static u64 rdtsc_prev = 0;
+	u64 rdtsc_real = rdtsc();
+
+	if(print_once)
+	{
+		printk("[handle_rdtsc] fake rdtsc svm function is working\n");
+		print_once = 0;
+		rdtsc_fake = rdtsc_real;
+	}
+
+	if(rdtsc_prev != 0)
+	{
+		if(rdtsc_real > rdtsc_prev)
+		{
+			u64 diff = rdtsc_real - rdtsc_prev;
+			u64 fake_diff =  diff / 20; // if you have 3.2Ghz on your vm, change 20 to 16
+			rdtsc_fake += fake_diff;
+		}
+	}
+	if(rdtsc_fake > rdtsc_real)
+	{
+		rdtsc_fake = rdtsc_real;
+	}
+	rdtsc_prev = rdtsc_real;
+
+	vcpu->arch.regs[VCPU_REGS_RAX] = rdtsc_fake & -1u;
+	vcpu->arch.regs[VCPU_REGS_RDX] = (rdtsc_fake >> 32) & -1u;
+
+	return svm_skip_emulated_instruction(vcpu);
+}
+
 static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[SVM_EXIT_READ_CR0]			= cr_interception,
 	[SVM_EXIT_READ_CR3]			= cr_interception,
@@ -3360,6 +3397,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 #ifdef CONFIG_KVM_AMD_SEV
 	[SVM_EXIT_VMGEXIT]			= sev_handle_vmgexit,
 #endif
+	[SVM_EXIT_RDTSC]			= handle_rdtsc_interception,
 };
 
 static void dump_vmcb(struct kvm_vcpu *vcpu)