[PATCH kvm-unit-tests 3/4] Add support for calling a function in guest mode

[Avi Kivity <avi@redhat.com>]

This patch provides a way to establish an "identity" guest which has
a 1:1 gva->hva translation.  This allows the host to switch to guest
mode, call a function in the same address space, and return.

Because long mode virtual addresses are 47 bits long, and some hosts
have smaller physical addresses, we target 32-bit mode only.  On
x86_64 the code needs to be run with 'setarch i386 -3' to limit the
address space to 3GB, so the address space occupied by the local
APIC is left unused.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 api/identity.cc       |   76 +++++++++++++++++++++++++++++++++++++++++++++++++
 api/identity.h        |   28 ++++++++++++++++++
 config-x86-common.mak |    2 +
 3 files changed, 106 insertions(+), 0 deletions(-)
 create mode 100644 api/identity.cc
 create mode 100644 api/identity.h

diff --git a/api/identity.cc b/api/identity.cc
new file mode 100644
index 0000000..8e86db1
--- /dev/null
+++ b/api/identity.cc
@@ -0,0 +1,76 @@
+
+#include "identity.h"
+#include <stdio.h>
+
+namespace identity {
+
+typedef unsigned long ulong;
+
+void setup_vm(kvm::vm& vm)
+{
+    vm.set_memory_region(0, NULL, 0, 3UL << 30);
+    vm.set_tss_addr(3UL << 30);
+}
+
+void vcpu::setup_sregs()
+{
+    kvm_sregs sregs = { };
+    kvm_segment dseg = { };
+    dseg.base = 0; dseg.limit = -1U; dseg.type = 3; dseg.present = 1;
+    dseg.dpl = 3; dseg.db = 1; dseg.s = 1; dseg.l = 0; dseg.g = 1;
+    kvm_segment cseg = dseg;
+    cseg.type = 11;
+
+    sregs.cs = cseg; asm ("mov %%cs, %0" : "=rm"(sregs.cs.selector));
+    sregs.ds = dseg; asm ("mov %%ds, %0" : "=rm"(sregs.ds.selector));
+    sregs.es = dseg; asm ("mov %%es, %0" : "=rm"(sregs.es.selector));
+    sregs.fs = dseg; asm ("mov %%fs, %0" : "=rm"(sregs.fs.selector));
+    sregs.gs = dseg; asm ("mov %%gs, %0" : "=rm"(sregs.gs.selector));
+    sregs.ss = dseg; asm ("mov %%ss, %0" : "=rm"(sregs.ss.selector));
+
+    uint32_t gsbase;
+    asm ("mov %%gs:0, %0" : "=r"(gsbase));
+    sregs.gs.base = gsbase;
+
+    sregs.tr.base = reinterpret_cast<ulong>(&*_stack.begin());
+    sregs.tr.type = 11;
+    sregs.tr.s = 0;
+    sregs.tr.present = 1;
+
+    sregs.cr0 = 0x11; /* PE, ET, !PG */
+    sregs.cr4 = 0;
+    sregs.efer = 0;
+    sregs.apic_base = 0xfee00000;
+    _vcpu.set_sregs(sregs);
+}
+
+void vcpu::thunk(vcpu* zis)
+{
+    zis->_guest_func();
+    asm volatile("outb %%al, %%dx" : : "a"(0), "d"(0));
+}
+
+void vcpu::setup_regs()
+{
+    kvm_regs regs = {};
+    regs.rflags = 0x3202;
+    regs.rsp = reinterpret_cast<ulong>(&*_stack.end());
+    regs.rsp &= ~15UL;
+    ulong* sp = reinterpret_cast<ulong *>(regs.rsp);
+    *--sp = reinterpret_cast<ulong>((char*)this);
+    *--sp = 0;
+    regs.rsp = reinterpret_cast<ulong>(sp);
+    regs.rip = reinterpret_cast<ulong>(&vcpu::thunk);
+    printf("rip %llx\n", regs.rip);
+    _vcpu.set_regs(regs);
+}
+
+vcpu::vcpu(kvm::vcpu& vcpu, boost::function<void ()> guest_func,
+           unsigned long stack_size)
+    : _vcpu(vcpu), _guest_func(guest_func), _stack(stack_size)
+{
+    setup_sregs();
+    setup_regs();
+}
+
+}
diff --git a/api/identity.h b/api/identity.h
new file mode 100644
index 0000000..025177a
--- /dev/null
+++ b/api/identity.h
@@ -0,0 +1,28 @@
+#ifndef API_IDENTITY_H
+#define API_IDENTITY_H
+
+#include "kvmxx.h"
+#include <boost/function.hpp>
+#include <vector>
+
+namespace identity {
+
+void setup_vm(kvm::vm& vm);
+
+class vcpu {
+public:
+    vcpu(kvm::vcpu& vcpu, boost::function<void ()> guest_func,
+	 unsigned long stack_size = 256 * 1024);
+private:
+    static void thunk(vcpu* vcpu);
+    void setup_regs();
+    void setup_sregs();
+private:
+    kvm::vcpu& _vcpu;
+    boost::function<void ()> _guest_func;
+    std::vector<char> _stack;
+};
+
+}
+
+#endif
diff --git a/config-x86-common.mak b/config-x86-common.mak
index b541c1c..0f3387b 100644
--- a/config-x86-common.mak
+++ b/config-x86-common.mak
@@ -79,3 +79,5 @@ arch_clean:
 	$(TEST_DIR)/.*.d $(TEST_DIR)/lib/.*.d $(TEST_DIR)/lib/*.o
 
 -include $(TEST_DIR)/.*.d lib/.*.d lib/x86/.*.d
+
+api/%.o: CFLAGS += -m32
\ No newline at end of file
-- 
1.7.1