KVM: selftests: Add option to run dirty_log_perf_test vCPUs in L2

Add an option to dirty_log_perf_test that configures the vCPUs to run in
L2 instead of L1. This makes it possible to benchmark the dirty logging
performance of nested virtualization, which is particularly interesting
because KVM must shadow L1's EPT/NPT tables.

For now this support only works on x86_64 CPUs with VMX. Otherwise
passing -n results in the test being skipped.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220520233249.3776001-11-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 127 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/lib/x86_64/perf_test_util.c b/tools/testing/selftests/kvm/lib/x86_64/perf_test_util.c
new file mode 100644
index 000000000000..e258524435a0
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86_64/perf_test_util.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * x86_64-specific extensions to perf_test_util.c.
+ *
+ * Copyright (C) 2022, Google, Inc.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "perf_test_util.h"
+#include "../kvm_util_internal.h"
+#include "processor.h"
+#include "vmx.h"
+
+void perf_test_l2_guest_code(uint64_t vcpu_id)
+{
+	perf_test_guest_code(vcpu_id);
+	vmcall();
+}
+
+extern char perf_test_l2_guest_entry[];
+__asm__(
+"perf_test_l2_guest_entry:"
+"	mov (%rsp), %rdi;"
+"	call perf_test_l2_guest_code;"
+"	ud2;"
+);
+
+static void perf_test_l1_guest_code(struct vmx_pages *vmx, uint64_t vcpu_id)
+{
+#define L2_GUEST_STACK_SIZE 64
+	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+	unsigned long *rsp;
+
+	GUEST_ASSERT(vmx->vmcs_gpa);
+	GUEST_ASSERT(prepare_for_vmx_operation(vmx));
+	GUEST_ASSERT(load_vmcs(vmx));
+	GUEST_ASSERT(ept_1g_pages_supported());
+
+	rsp = &l2_guest_stack[L2_GUEST_STACK_SIZE - 1];
+	*rsp = vcpu_id;
+	prepare_vmcs(vmx, perf_test_l2_guest_entry, rsp);
+
+	GUEST_ASSERT(!vmlaunch());
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
+	GUEST_DONE();
+}
+
+uint64_t perf_test_nested_pages(int nr_vcpus)
+{
+	/*
+	 * 513 page tables is enough to identity-map 256 TiB of L2 with 1G
+	 * pages and 4-level paging, plus a few pages per-vCPU for data
+	 * structures such as the VMCS.
+	 */
+	return 513 + 10 * nr_vcpus;
+}
+
+void perf_test_setup_ept(struct vmx_pages *vmx, struct kvm_vm *vm)
+{
+	uint64_t start, end;
+
+	prepare_eptp(vmx, vm, 0);
+
+	/*
+	 * Identity map the first 4G and the test region with 1G pages so that
+	 * KVM can shadow the EPT12 with the maximum huge page size supported
+	 * by the backing source.
+	 */
+	nested_identity_map_1g(vmx, vm, 0, 0x100000000ULL);
+
+	start = align_down(perf_test_args.gpa, PG_SIZE_1G);
+	end = align_up(perf_test_args.gpa + perf_test_args.size, PG_SIZE_1G);
+	nested_identity_map_1g(vmx, vm, start, end - start);
+}
+
+void perf_test_setup_nested(struct kvm_vm *vm, int nr_vcpus)
+{
+	struct vmx_pages *vmx, *vmx0 = NULL;
+	struct kvm_regs regs;
+	vm_vaddr_t vmx_gva;
+	int vcpu_id;
+
+	nested_vmx_check_supported();
+
+	for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
+		vmx = vcpu_alloc_vmx(vm, &vmx_gva);
+
+		if (vcpu_id == 0) {
+			perf_test_setup_ept(vmx, vm);
+			vmx0 = vmx;
+		} else {
+			/* Share the same EPT table across all vCPUs. */
+			vmx->eptp = vmx0->eptp;
+			vmx->eptp_hva = vmx0->eptp_hva;
+			vmx->eptp_gpa = vmx0->eptp_gpa;
+		}
+
+		/*
+		 * Override the vCPU to run perf_test_l1_guest_code() which will
+		 * bounce it into L2 before calling perf_test_guest_code().
+		 */
+		vcpu_regs_get(vm, vcpu_id, &regs);
+		regs.rip = (unsigned long) perf_test_l1_guest_code;
+		vcpu_regs_set(vm, vcpu_id, &regs);
+		vcpu_args_set(vm, vcpu_id, 2, vmx_gva, vcpu_id);
+	}
+}
diff --git a/tools/testing/selftests/kvm/lib/x86_64/vmx.c b/tools/testing/selftests/kvm/lib/x86_64/vmx.c
index 5bf169179455..b77a01d0a271 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/vmx.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/vmx.c
@@ -203,6 +203,11 @@ static bool ept_vpid_cap_supported(uint64_t mask)
 	return rdmsr(MSR_IA32_VMX_EPT_VPID_CAP) & mask;
 }
 
+bool ept_1g_pages_supported(void)
+{
+	return ept_vpid_cap_supported(VMX_EPT_VPID_CAP_1G_PAGES);
+}
+
 /*
  * Initialize the control fields to the most basic settings possible.
  */
@@ -439,6 +444,9 @@ void __nested_pg_map(struct vmx_pages *vmx, struct kvm_vm *vm,
 	TEST_ASSERT(vm->mode == VM_MODE_PXXV48_4K, "Attempt to use "
 		    "unknown or unsupported guest mode, mode: 0x%x", vm->mode);
 
+	TEST_ASSERT((nested_paddr >> 48) == 0,
+		    "Nested physical address 0x%lx requires 5-level paging",
+		    nested_paddr);
 	TEST_ASSERT((nested_paddr % page_size) == 0,
 		    "Nested physical address not on page boundary,\n"
 		    "  nested_paddr: 0x%lx page_size: 0x%lx",
@@ -547,6 +555,13 @@ void nested_map_memslot(struct vmx_pages *vmx, struct kvm_vm *vm,
 	}
 }
 
+/* Identity map a region with 1GiB Pages. */
+void nested_identity_map_1g(struct vmx_pages *vmx, struct kvm_vm *vm,
+			    uint64_t addr, uint64_t size)
+{
+	__nested_map(vmx, vm, addr, addr, size, PG_LEVEL_1G);
+}
+
 void prepare_eptp(struct vmx_pages *vmx, struct kvm_vm *vm,
 		  uint32_t eptp_memslot)
 {