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// SPDX-License-Identifier: GPL-2.0
/*
* ucall support. A ucall is a "hypercall to userspace".
*
* Copyright (C) 2018, Red Hat, Inc.
*/
#include "kvm_util.h"
#define UCALL_PIO_PORT ((uint16_t)0x1000)
void ucall_arch_do_ucall(vm_vaddr_t uc)
{
/*
* FIXME: Revert this hack (the entire commit that added it) once nVMX
* preserves L2 GPRs across a nested VM-Exit. If a ucall from L2, e.g.
* to do a GUEST_SYNC(), lands the vCPU in L1, any and all GPRs can be
* clobbered by L1. Save and restore non-volatile GPRs (clobbering RBP
* in particular is problematic) along with RDX and RDI (which are
* inputs), and clobber volatile GPRs. *sigh*
*/
#define HORRIFIC_L2_UCALL_CLOBBER_HACK \
"rcx", "rsi", "r8", "r9", "r10", "r11"
asm volatile("push %%rbp\n\t"
"push %%r15\n\t"
"push %%r14\n\t"
"push %%r13\n\t"
"push %%r12\n\t"
"push %%rbx\n\t"
"push %%rdx\n\t"
"push %%rdi\n\t"
"in %[port], %%al\n\t"
"pop %%rdi\n\t"
"pop %%rdx\n\t"
"pop %%rbx\n\t"
"pop %%r12\n\t"
"pop %%r13\n\t"
"pop %%r14\n\t"
"pop %%r15\n\t"
"pop %%rbp\n\t"
: : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory",
HORRIFIC_L2_UCALL_CLOBBER_HACK);
}
void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
{
struct kvm_run *run = vcpu->run;
if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
struct kvm_regs regs;
vcpu_regs_get(vcpu, ®s);
return (void *)regs.rdi;
}
return NULL;
}
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