KVM: x86/xen: intercept xen hypercalls if enabled

Add a new exit reason for emulator to handle Xen hypercalls.

Since this means KVM owns the ABI, dispense with the facility for the
VMM to provide its own copy of the hypercall pages; just fill them in
directly using VMCALL/VMMCALL as we do for the Hyper-V hypercall page.

This behaviour is enabled by a new INTERCEPT_HCALL flag in the
KVM_XEN_HVM_CONFIG ioctl structure, and advertised by the same flag
being returned from the KVM_CAP_XEN_HVM check.

Rename xen_hvm_config() to kvm_xen_write_hypercall_page() and move it
to the nascent xen.c while we're at it, and add a test case.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

3 files changed, 125 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 9616f77cc5af..be9613dd6d9b 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -62,6 +62,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/xss_msr_test
 TEST_GEN_PROGS_x86_64 += x86_64/debug_regs
 TEST_GEN_PROGS_x86_64 += x86_64/tsc_msrs_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_pmu_msrs_test
+TEST_GEN_PROGS_x86_64 += x86_64/xen_vmcall_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index fa5a90e6c6f0..d787cb802b4a 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1801,6 +1801,7 @@ static struct exit_reason {
 	{KVM_EXIT_DIRTY_RING_FULL, "DIRTY_RING_FULL"},
 	{KVM_EXIT_X86_RDMSR, "RDMSR"},
 	{KVM_EXIT_X86_WRMSR, "WRMSR"},
+	{KVM_EXIT_XEN, "XEN"},
 #ifdef KVM_EXIT_MEMORY_NOT_PRESENT
 	{KVM_EXIT_MEMORY_NOT_PRESENT, "MEMORY_NOT_PRESENT"},
 #endif
diff --git a/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c b/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
new file mode 100644
index 000000000000..234c9da286aa
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * xen_vmcall_test
+ *
+ * Copyright © 2020 Amazon.com, Inc. or its affiliates.
+ *
+ * Userspace hypercall testing
+ */
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+#define VCPU_ID		5
+
+#define HCALL_REGION_GPA	0xc0000000ULL
+#define HCALL_REGION_SLOT	10
+
+static struct kvm_vm *vm;
+
+#define INPUTVALUE 17
+#define ARGVALUE(x) (0xdeadbeef5a5a0000UL + x)
+#define RETVALUE 0xcafef00dfbfbffffUL
+
+#define XEN_HYPERCALL_MSR 0x40000000
+
+static void guest_code(void)
+{
+	unsigned long rax = INPUTVALUE;
+	unsigned long rdi = ARGVALUE(1);
+	unsigned long rsi = ARGVALUE(2);
+	unsigned long rdx = ARGVALUE(3);
+	register unsigned long r10 __asm__("r10") = ARGVALUE(4);
+	register unsigned long r8 __asm__("r8") = ARGVALUE(5);
+	register unsigned long r9 __asm__("r9") = ARGVALUE(6);
+
+	/* First a direct invocation of 'vmcall' */
+	__asm__ __volatile__("vmcall" :
+			     "=a"(rax) :
+			     "a"(rax), "D"(rdi), "S"(rsi), "d"(rdx),
+			     "r"(r10), "r"(r8), "r"(r9));
+	GUEST_ASSERT(rax == RETVALUE);
+
+	/* Now fill in the hypercall page */
+	__asm__ __volatile__("wrmsr" : : "c" (XEN_HYPERCALL_MSR),
+			     "a" (HCALL_REGION_GPA & 0xffffffff),
+			     "d" (HCALL_REGION_GPA >> 32));
+
+	/* And invoke the same hypercall that way */
+	__asm__ __volatile__("call *%1" : "=a"(rax) :
+			     "r"(HCALL_REGION_GPA + INPUTVALUE * 32),
+			     "a"(rax), "D"(rdi), "S"(rsi), "d"(rdx),
+			     "r"(r10), "r"(r8), "r"(r9));
+	GUEST_ASSERT(rax == RETVALUE);
+
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	if (!(kvm_check_cap(KVM_CAP_XEN_HVM) &
+	      KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL) ) {
+		print_skip("KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL not available");
+		exit(KSFT_SKIP);
+	}
+
+	vm = vm_create_default(VCPU_ID, 0, (void *) guest_code);
+	vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
+
+	struct kvm_xen_hvm_config hvmc = {
+		.flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL,
+		.msr = XEN_HYPERCALL_MSR,
+	};
+	vm_ioctl(vm, KVM_XEN_HVM_CONFIG, &hvmc);
+
+	/* Map a region for the hypercall page */
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+                                    HCALL_REGION_GPA, HCALL_REGION_SLOT,
+				    getpagesize(), 0);
+	virt_map(vm, HCALL_REGION_GPA, HCALL_REGION_GPA, 1, 0);
+
+	for (;;) {
+		volatile struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+		struct ucall uc;
+
+		vcpu_run(vm, VCPU_ID);
+
+		if (run->exit_reason == KVM_EXIT_XEN) {
+			ASSERT_EQ(run->xen.type, KVM_EXIT_XEN_HCALL);
+			ASSERT_EQ(run->xen.u.hcall.cpl, 0);
+			ASSERT_EQ(run->xen.u.hcall.longmode, 1);
+			ASSERT_EQ(run->xen.u.hcall.input, INPUTVALUE);
+			ASSERT_EQ(run->xen.u.hcall.params[0], ARGVALUE(1));
+			ASSERT_EQ(run->xen.u.hcall.params[1], ARGVALUE(2));
+			ASSERT_EQ(run->xen.u.hcall.params[2], ARGVALUE(3));
+			ASSERT_EQ(run->xen.u.hcall.params[3], ARGVALUE(4));
+			ASSERT_EQ(run->xen.u.hcall.params[4], ARGVALUE(5));
+			ASSERT_EQ(run->xen.u.hcall.params[5], ARGVALUE(6));
+			run->xen.u.hcall.result = RETVALUE;
+			continue;
+		}
+
+		TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+			    "Got exit_reason other than KVM_EXIT_IO: %u (%s)\n",
+			    run->exit_reason,
+			    exit_reason_str(run->exit_reason));
+
+		switch (get_ucall(vm, VCPU_ID, &uc)) {
+		case UCALL_ABORT:
+			TEST_FAIL("%s", (const char *)uc.args[0]);
+			/* NOT REACHED */
+		case UCALL_SYNC:
+			break;
+		case UCALL_DONE:
+			goto done;
+		default:
+			TEST_FAIL("Unknown ucall 0x%lx.", uc.cmd);
+		}
+	}
+done:
+	kvm_vm_free(vm);
+	return 0;
+}