ucall.c

 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
11void 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
45void *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, &regs);
53		return (void *)regs.rdi;
54	}
55	return NULL;
56}