[PATCH] KVM: selftests: Detect max PA width from cpuid

[Peter Xu]

The dirty_log_test is failing on some old machines like Xeon E3-1220
with tripple faults when writting to the tracked memory region:

  Test iterations: 32, interval: 10 (ms)
  Testing guest mode: PA-bits:52, VA-bits:48, 4K pages
  guest physical test memory offset: 0x7fbffef000
  ==== Test Assertion Failure ====
  dirty_log_test.c:138: false
  pid=6137 tid=6139 - Success
     1  0x0000000000401ca1: vcpu_worker at dirty_log_test.c:138
     2  0x00007f3dd9e392dd: ?? ??:0
     3  0x00007f3dd9b6a132: ?? ??:0
  Invalid guest sync status: exit_reason=SHUTDOWN

It's because previously we moved the testing memory region from a
static place (1G) to the top of the system's physical address space,
meanwhile we stick to 39 bits PA for all the x86_64 machines.  That's
not true for machines like Xeon E3-1220 where it only supports 36.

Let's unbreak this test by dynamically detect PA width from CPUID
0x80000008.  Meanwhile, even allow kvm_get_supported_cpuid_index() to
fail.  I don't know whether that could be useful because I think
0x80000008 should be there for all x86_64 hosts, but I also think it's
not really helpful to assert in the kvm_get_supported_cpuid_index().

Fixes: b442324b581556e
CC: Paolo Bonzini <pbonzini@xxxxxxxxxx>
CC: Andrew Jones <drjones@xxxxxxxxxx>
CC: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
CC: Thomas Huth <thuth@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/dirty_log_test.c  | 22 +++++++++++++------
 .../selftests/kvm/lib/x86_64/processor.c      |  3 ---
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index ceb52b952637..111592f3a1d7 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -274,18 +274,26 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 	DEBUG("Testing guest mode: %s\n", vm_guest_mode_string(mode));
 
 #ifdef __x86_64__
-	/*
-	 * FIXME
-	 * The x86_64 kvm selftests framework currently only supports a
-	 * single PML4 which restricts the number of physical address
-	 * bits we can change to 39.
-	 */
-	guest_pa_bits = 39;
+	{
+		struct kvm_cpuid_entry2 *entry;
+
+		entry = kvm_get_supported_cpuid_entry(0x80000008);
+		/*
+		 * Supported PA width can be smaller than 52 even if
+		 * we're with VM_MODE_P52V48_4K mode.  Fetch it from
+		 * the host to update the default value (SDM 4.1.4).
+		 */
+		if (entry)
+			guest_pa_bits = entry->eax & 0xff;
+		else
+			guest_pa_bits = 32;
+	}
 #endif
 #ifdef __aarch64__
 	if (guest_pa_bits != 40)
 		type = KVM_VM_TYPE_ARM_IPA_SIZE(guest_pa_bits);
 #endif
+	printf("Supported guest physical address width: %d\n", guest_pa_bits);
 	max_gfn = (1ul << (guest_pa_bits - guest_page_shift)) - 1;
 	guest_page_size = (1ul << guest_page_shift);
 	/*
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 6cb34a0fa200..9de2fd310ac8 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -760,9 +760,6 @@ kvm_get_supported_cpuid_index(uint32_t function, uint32_t index)
 			break;
 		}
 	}
-
-	TEST_ASSERT(entry, "Guest CPUID entry not found: (EAX=%x, ECX=%x).",
-		    function, index);
 	return entry;
 }
 
-- 
2.21.0