>From 5d7427ace0a94f842610a9823d5230335dbae301 Mon Sep 17 00:00:00 2001
From: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Subject: [PATCH] lkvm: hack the fpu for fun and profit.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
---
 tools/kvm/kvm-cpu.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git tools/kvm/kvm-cpu.c tools/kvm/kvm-cpu.c
index 5d90664..87d9641 100644
--- tools/kvm/kvm-cpu.c
+++ tools/kvm/kvm-cpu.c
@@ -30,6 +30,65 @@ void kvm_cpu__enable_singlestep(struct kvm_cpu *vcpu)
 		pr_warning("KVM_SET_GUEST_DEBUG failed");
 }
 
+static struct kvm_xsave xsave;
+
+static void kvm__sighandler(int signum, siginfo_t* infop, void* context_p)
+{
+	ucontext_t* context = context_p;
+	struct sigcontext* scontext = (void *) &context->uc_mcontext;
+	struct _fpstate* fpstate = scontext->fpstate;
+	/* uint64_t* xstate_bv = (void*) (fpstate + 1); */
+	/* uint64_t* xcomp_bv = xstate_bv + 1; */
+
+	memcpy(&xsave, fpstate, sizeof(*fpstate));
+
+	return;
+}
+
+static void kvm__install_handler(void)
+{
+	struct sigaction sa = {
+		.sa_sigaction = kvm__sighandler
+	};
+
+	sigfillset(&sa.sa_mask);
+	sa.sa_flags = SA_SIGINFO;
+
+	sigaction(SIGUSR1, &sa, NULL);
+}
+
+static void kvm__copy_xsave_from_signal_stack(void)
+{
+	static int already_installed = 0;
+
+	if (already_installed)
+		return;
+
+	kvm__install_handler();
+	raise(SIGUSR1);
+	already_installed = 1;
+}
+
+static void kvm__hijack_xsave(struct kvm_cpu* vcpu)
+{
+	int err = 0;
+	struct _fpstate *fpstate = (void*) &xsave;
+
+	fpstate->mxcsr = ~0U;
+
+	err = ioctl(vcpu->vcpu_fd, KVM_SET_XSAVE, fpstate);
+	if (err)
+		die_perror("KVM_GET_XSAVE failed");
+}
+
+static void kvm_cpu__mess_fpu(struct kvm_cpu* vcpu)
+{
+	kvm__copy_xsave_from_signal_stack();
+	kvm__hijack_xsave(vcpu);
+
+	return;
+}
+
 void kvm_cpu__run(struct kvm_cpu *vcpu)
 {
 	int err;
@@ -37,6 +96,8 @@ void kvm_cpu__run(struct kvm_cpu *vcpu)
 	if (!vcpu->is_running)
 		return;
 
+	kvm_cpu__mess_fpu(vcpu);
+
 	err = ioctl(vcpu->vcpu_fd, KVM_RUN, 0);
 	if (err < 0 && (errno != EINTR && errno != EAGAIN))
 		die_perror("KVM_RUN failed");
-- 
2.0.5