| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ======================================= |
| Internal ABI between the kernel and HYP |
| ======================================= |
| |
| This file documents the interaction between the Linux kernel and the |
| hypervisor layer when running Linux as a hypervisor (for example |
| KVM). It doesn't cover the interaction of the kernel with the |
| hypervisor when running as a guest (under Xen, KVM or any other |
| hypervisor), or any hypervisor-specific interaction when the kernel is |
| used as a host. |
| |
| Note: KVM/arm has been removed from the kernel. The API described |
| here is still valid though, as it allows the kernel to kexec when |
| booted at HYP. It can also be used by a hypervisor other than KVM |
| if necessary. |
| |
| On arm and arm64 (without VHE), the kernel doesn't run in hypervisor |
| mode, but still needs to interact with it, allowing a built-in |
| hypervisor to be either installed or torn down. |
| |
| In order to achieve this, the kernel must be booted at HYP (arm) or |
| EL2 (arm64), allowing it to install a set of stubs before dropping to |
| SVC/EL1. These stubs are accessible by using a 'hvc #0' instruction, |
| and only act on individual CPUs. |
| |
| Unless specified otherwise, any built-in hypervisor must implement |
| these functions (see arch/arm{,64}/include/asm/virt.h): |
| |
| * :: |
| |
| r0/x0 = HVC_SET_VECTORS |
| r1/x1 = vectors |
| |
| Set HVBAR/VBAR_EL2 to 'vectors' to enable a hypervisor. 'vectors' |
| must be a physical address, and respect the alignment requirements |
| of the architecture. Only implemented by the initial stubs, not by |
| Linux hypervisors. |
| |
| * :: |
| |
| r0/x0 = HVC_RESET_VECTORS |
| |
| Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials |
| stubs' exception vector value. This effectively disables an existing |
| hypervisor. |
| |
| * :: |
| |
| r0/x0 = HVC_SOFT_RESTART |
| r1/x1 = restart address |
| x2 = x0's value when entering the next payload (arm64) |
| x3 = x1's value when entering the next payload (arm64) |
| x4 = x2's value when entering the next payload (arm64) |
| |
| Mask all exceptions, disable the MMU, clear I+D bits, move the arguments |
| into place (arm64 only), and jump to the restart address while at HYP/EL2. |
| This hypercall is not expected to return to its caller. |
| |
| Any other value of r0/x0 triggers a hypervisor-specific handling, |
| which is not documented here. |
| |
| The return value of a stub hypercall is held by r0/x0, and is 0 on |
| success, and HVC_STUB_ERR on error. A stub hypercall is allowed to |
| clobber any of the caller-saved registers (x0-x18 on arm64, r0-r3 and |
| ip on arm). It is thus recommended to use a function call to perform |
| the hypercall. |