Some improvements.

[giuseppejaripappalardo]

Hello, thanks for your nice work.

I would like to propose some fine tuning, up to you if bring or not:

static int handle_rdtsc(struct kvm_vcpu *vcpu)
{
// Static variables to keep track of the fake and previous TSC values
static u64 rdtsc_fake = 0;
static u64 rdtsc_prev = 0;
// Static variable for the divisor, makes it easy to adjust the TSC rate
static const u64 divisore = 16;

// Retrieve the real TSC value
u64 rdtsc_real = rdtsc();

// Check if this is the first run of the function
if (print_once) {
    printk("[handle_rdtsc] fake rdtsc vmx function is working\n");
    print_once = 0; // Ensure this block runs only once
    rdtsc_fake = rdtsc_real; // Initialize the fake TSC value
}

// Calculate the fake TSC value if not the first run
if (rdtsc_prev != 0 && rdtsc_real > rdtsc_prev) {
    u64 diff = rdtsc_real - rdtsc_prev;
    u64 fake_diff = diff / divisore; // Calculate the difference to be added to the fake TSC
    rdtsc_fake += fake_diff;
} else if (rdtsc_prev == 0) {
    // Handle the initial case where rdtsc_prev is zero
    rdtsc_fake = rdtsc_real;
}

// Prevent the fake TSC from regressing or exceeding the real TSC
if (rdtsc_fake < rdtsc_prev || rdtsc_fake > rdtsc_real) {
    rdtsc_fake = rdtsc_prev + (rdtsc_real - rdtsc_prev) / divisore;
}

// Update the previous TSC value
rdtsc_prev = rdtsc_real;

// Set the fake TSC value to the VM's CPU registers
vcpu->arch.regs[VCPU_REGS_RAX] = rdtsc_fake & -1u;
vcpu->arch.regs[VCPU_REGS_RDX] = (rdtsc_fake >> 32) & -1u;  

// Skip the emulated instruction and return
return skip_emulated_instruction(vcpu);

}

Regards,
Jari

[felikcat]

This patch makes Windows 10 crash no matter what on 'IPI_WATCHDOG_TIMEOUT' on a i7 12700K.

The unmodified patch works as intended with no BSOD.

I've done the following to make these patches work on kernel 6.9;
in vmx.c:

        /*
	 * Not used by KVM, but fully supported for nesting, i.e. are allowed in
	 * vmcs12 and propagated to vmcs02 when set in vmcs12.
	 */
	exec_control &= ~(CPU_BASED_USE_IO_BITMAPS |
			  CPU_BASED_MONITOR_TRAP_FLAG |
			  CPU_BASED_PAUSE_EXITING);

	// Ensure handle_rdtsc() is used.
	exec_control |= CPU_BASED_RDTSC_EXITING;

In vmx.h:

#define __KVM_REQUIRED_VMX_CPU_BASED_VM_EXEC_CONTROL			\
	(CPU_BASED_HLT_EXITING |					\
	 CPU_BASED_CR3_LOAD_EXITING |					\
	 CPU_BASED_CR3_STORE_EXITING |					\
	 CPU_BASED_UNCOND_IO_EXITING |					\
	 CPU_BASED_MOV_DR_EXITING |					\
	 CPU_BASED_USE_TSC_OFFSETTING |					\
	 CPU_BASED_MWAIT_EXITING |					\
	 CPU_BASED_MONITOR_EXITING |					\
	 CPU_BASED_INVLPG_EXITING |					\
	 CPU_BASED_RDPMC_EXITING |					\
	 CPU_BASED_RDTSC_EXITING |                                      \
	 CPU_BASED_INTR_WINDOW_EXITING)