diff --git a/src/transport/mod.rs b/src/transport/mod.rs index f166ac3c..5741e7f1 100644 --- a/src/transport/mod.rs +++ b/src/transport/mod.rs @@ -4,6 +4,8 @@ pub mod fake; pub mod mmio; pub mod pci; +#[cfg(target_arch = "x86_64")] +pub mod x86_64; use crate::{PhysAddr, Result, PAGE_SIZE}; use bitflags::{bitflags, Flags}; diff --git a/src/transport/x86_64.rs b/src/transport/x86_64.rs new file mode 100644 index 00000000..d8e1eb4c --- /dev/null +++ b/src/transport/x86_64.rs @@ -0,0 +1,124 @@ +//! x86-64 specific transports. + +use super::pci::bus::{Cam, ConfigurationAccess, DeviceFunction}; +use core::arch::asm; + +/// This CPUID returns the signature and should be used to determine if VM is running under pKVM, +/// KVM or not. See the Linux header `arch/x86/include/uapi/asm/kvm_para.h`. +const KVM_CPUID_SIGNATURE: u32 = 0x40000000; + +// See `include/uapi/linux/kvm_para.h`. (These hypercalls numbers can change depending on the +// upstream progress.) +const KVM_HC_PKVM_OP: u32 = 20; +const PKVM_GHC_IOREAD: u32 = KVM_HC_PKVM_OP + 3; +const PKVM_GHC_IOWRITE: u32 = KVM_HC_PKVM_OP + 4; + +const PKVM_SIGNATURE: &[u8] = b"PKVM"; + +/// A PCI configuration access mechanism using hypercalls implemented by the x86-64 pKVM hypervisor. +pub struct HypCam { + /// The physical base address of the PCI root complex. + phys_base: usize, + cam: Cam, +} + +impl HypCam { + /// Creates a new `HypCam` for the PCI root complex at the given physical base address. + pub fn new(phys_base: usize, cam: Cam) -> Self { + Self { phys_base, cam } + } + + /// Returns whether we are running under pKVM by checking the CPU ID signature. + pub fn is_pkvm() -> bool { + cpuid_signature() == PKVM_SIGNATURE + } +} + +impl ConfigurationAccess for HypCam { + fn read_word(&self, device_function: DeviceFunction, register_offset: u8) -> u32 { + let address = self.cam.cam_offset(device_function, register_offset); + hyp_io_read(self.phys_base + (address as usize), 4) + } + + fn write_word(&mut self, device_function: DeviceFunction, register_offset: u8, data: u32) { + let address = self.cam.cam_offset(device_function, register_offset); + hyp_io_write(self.phys_base + (address as usize), 4, data); + } + + unsafe fn unsafe_clone(&self) -> Self { + Self { + phys_base: self.phys_base, + cam: self.cam, + } + } +} + +/// Gets the signature CPU ID. +fn cpuid_signature() -> [u8; 4] { + let signature: u32; + unsafe { + // The argument for cpuid is passed via rax and in case of KVM_CPUID_SIGNATURE returned via + // rbx, rcx and rdx. Ideally using a named argument in inline asm for rbx would be more + // straightforward, but when "rbx" is directly used LLVM complains that it is used + // internally. + // + // Therefore use r8 instead and push rbx to the stack before making cpuid call, store + // rbx content to r8 as use it as inline asm output and pop the rbx. + asm!( + "push rbx", + "cpuid", + "mov r8, rbx", + "pop rbx", + in("eax") KVM_CPUID_SIGNATURE, + out("r8") signature, + out("rcx") _, + out("rdx") _, + ); + }; + signature.to_le_bytes() +} + +/// Asks the hypervisor to perform an IO read at the given physical address. +fn hyp_io_read(address: usize, size: usize) -> u32 { + // Arguments for vmcall are passed via rax, rbx, rcx and rdx. Ideally using a named argument in + // the inline asm for rbx would be more straightforward, but when "rbx" is used directly LLVM + // complains that it is used internally. + // + // Therefore use r8 temporary, push rbx to the stack, perform proper call and pop rbx + // again + let data; + unsafe { + asm!( + "push rbx", + "mov rbx, r8", + "vmcall", + "pop rbx", + inout("rax") PKVM_GHC_IOREAD => data, + in("r8") address, + in("rcx") size, + ); + } + data +} + +/// Asks the hypervisor to perform an IO write at the given physical address. +fn hyp_io_write(address: usize, size: usize, data: u32) { + unsafe { + // Arguments for vmcall are passed via rax, rbx, rcx and rdx. Ideally using a named argument + // in the inline asm for rbx would be more straightforward but when "rbx" is used directly + // used LLVM complains that it is used internally. + // + // Therefore use r8 temporary, push rbx to the stack, perform proper call and pop rbx + // again + asm!( + "push rbx", + "mov rbx, r8", + "vmcall", + "pop rbx", + in("rax") PKVM_GHC_IOWRITE, + in("r8") address, + in("rcx") size, + in("rdx") data, + ); + } +}