1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * ucall support. A ucall is a "hypercall to userspace". 4 * 5 * Copyright (C) 2018, Red Hat, Inc. 6 */ 7 #include "kvm_util.h" 8 9 #define UCALL_PIO_PORT ((uint16_t)0x1000) 10 11 void ucall_arch_do_ucall(vm_vaddr_t uc) 12 { 13 /* 14 * FIXME: Revert this hack (the entire commit that added it) once nVMX 15 * preserves L2 GPRs across a nested VM-Exit. If a ucall from L2, e.g. 16 * to do a GUEST_SYNC(), lands the vCPU in L1, any and all GPRs can be 17 * clobbered by L1. Save and restore non-volatile GPRs (clobbering RBP 18 * in particular is problematic) along with RDX and RDI (which are 19 * inputs), and clobber volatile GPRs. *sigh* 20 */ 21 #define HORRIFIC_L2_UCALL_CLOBBER_HACK \ 22 "rcx", "rsi", "r8", "r9", "r10", "r11" 23 24 asm volatile("push %%rbp\n\t" 25 "push %%r15\n\t" 26 "push %%r14\n\t" 27 "push %%r13\n\t" 28 "push %%r12\n\t" 29 "push %%rbx\n\t" 30 "push %%rdx\n\t" 31 "push %%rdi\n\t" 32 "in %[port], %%al\n\t" 33 "pop %%rdi\n\t" 34 "pop %%rdx\n\t" 35 "pop %%rbx\n\t" 36 "pop %%r12\n\t" 37 "pop %%r13\n\t" 38 "pop %%r14\n\t" 39 "pop %%r15\n\t" 40 "pop %%rbp\n\t" 41 : : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory", 42 HORRIFIC_L2_UCALL_CLOBBER_HACK); 43 } 44 45 void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu) 46 { 47 struct kvm_run *run = vcpu->run; 48 49 if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) { 50 struct kvm_regs regs; 51 52 vcpu_regs_get(vcpu, ®s); 53 return (void *)regs.rdi; 54 } 55 return NULL; 56 } 57