// Inline asm wrappers.
//
// Userspace-callable: rdtsc, cpuid, svm_supported
// Ring-0 stubs: read_cr3, write_cr3, vmload, vmsave, vmrun, rdmsr, wrmsr
//   these are here for when this code runs in a kernel context
//   Calling them from userspace will #GP or #UD

/// Read the hardware timestamp counter (TSC)
/// Used for timing guest memory access patterns (cache-timing side channels)
#[inline(always)]
pub fn rdtsc() -> u64 {
    let lo: u32;
    let hi: u32;
    unsafe {
        core::arch::asm!(
            "rdtsc",
            out("eax") lo,
            out("edx") hi,
            options(nomem, nostack, preserves_flags),
        );
    }
    ((hi as u64) << 32) | lo as u64
}

/// CPUID — leaf + subleaf, returns (eax, ebx, ecx, edx).
/// rbx is LLVM-reserved so we save/restore it around the instruction.
pub fn cpuid(leaf: u32, subleaf: u32) -> (u32, u32, u32, u32) {
    let (eax, ebx, ecx, edx): (u32, u32, u32, u32);
    unsafe {
        core::arch::asm!(
            "push rbx",
            "cpuid",
            "mov {ebx_out:e}, ebx",
            "pop rbx",
            inout("eax") leaf    => eax,
            inout("ecx") subleaf => ecx,
            ebx_out = out(reg) ebx,
            out("edx") edx,
            options(nomem, nostack, preserves_flags),
        );
    }
    (eax, ebx, ecx, edx)
}

/// Possible delete only used to check for AMD SVM
/// Check whether the host CPU supports AMD SVM (CPUID 0x80000001 ECX bit 2).
pub fn svm_supported() -> bool {
    let (_, _, ecx, _) = cpuid(0x8000_0001, 0);
    ecx & (1 << 2) != 0
}

// All of these should fault at CPL > 0 (#GP or #UD).

unsafe extern "C" {
    /// Read host CR3.  Returns the physical address of the host PML4.
    pub fn read_cr3() -> u64;
    /// Write host CR3 — flushes all non-global TLB entries.
    pub fn write_cr3(cr3: u64);
    /// VMLOAD — loads guest state from the VMCB at the given physical address.  AMD SVM.
    pub fn vmload(vmcb_pa: u64);
    /// VMSAVE — saves guest state back to the VMCB at the given physical address.  AMD SVM.
    pub fn vmsave(vmcb_pa: u64);
    /// VMRUN — enters the guest.  Does not return until a #VMEXIT occurs.  AMD SVM.
    pub fn vmrun(vmcb_pa: u64);
    /// RDMSR — read model-specific register.
    pub fn rdmsr(msr: u32) -> u64;
    /// WRMSR — write model-specific register.
    pub fn wrmsr(msr: u32, val: u64);
}