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
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