[kvm-unit-tests] x86/tscdeadline_delay: test busy-wait loop in host

Commit Message

Thadeu Lima de Souza Cascardo Nov. 1, 2019, 2:14 p.m. UTC

When the tsc deadline is used, the host might use a busy wait loop, which
might sleep for up to the TSC offset/adjust, which is set when the guest
sets the TSC MSR.

Linux commit b606f189c7 ("KVM: LAPIC: cap __delay at lapic_timer_advance_ns")
fixes the issue and this test check for its regression.

On a kernel without that fix, the test fails with:
FAIL: delta: 4296500469

On a kernel with the fix, the max_delta is usually reported as very low
compared to that one:
max delta: 12423150

Signed-off-by: Thadeu Lima de Souza Cascardo <[e-mail]>
---
 x86/Makefile.x86_64     |   1 +
 x86/tscdeadline_delay.c | 105 ++++++++++++++++++++++++++++++++++++++++
 x86/unittests.cfg       |   4 ++
 3 files changed, 110 insertions(+)
 create mode 100644 x86/tscdeadline_delay.c

Patch

diff --git a/x86/Makefile.x86_64 b/x86/Makefile.x86_64
index 010102b600f9..ac0e4858a29c 100644
--- a/x86/Makefile.x86_64
+++ b/x86/Makefile.x86_64
@@ -17,6 +17,7 @@  tests += $(TEST_DIR)/syscall.flat
 tests += $(TEST_DIR)/svm.flat
 tests += $(TEST_DIR)/vmx.flat
 tests += $(TEST_DIR)/tscdeadline_latency.flat
+tests += $(TEST_DIR)/tscdeadline_delay.flat
 tests += $(TEST_DIR)/intel-iommu.flat
 tests += $(TEST_DIR)/vmware_backdoors.flat
 tests += $(TEST_DIR)/rdpru.flat
diff --git a/x86/tscdeadline_delay.c b/x86/tscdeadline_delay.c
new file mode 100644
index 000000000000..01498da2d0ce
--- /dev/null
+++ b/x86/tscdeadline_delay.c
@@ -0,0 +1,105 @@ 
+/* Test regression for bug fixed by linux commit b606f189c7 */
+
+#include "libcflat.h"
+#include "apic.h"
+#include "vm.h"
+#include "smp.h"
+#include "desc.h"
+#include "isr.h"
+#include "msr.h"
+
+static u64 expire;
+
+static void test_lapic_existence(void)
+{
+    u32 lvr;
+
+    lvr = apic_read(APIC_LVR);
+    printf("apic version: %x\n", lvr);
+    report("apic existence", (u16)lvr == 0x14);
+}
+
+#define TSC_DEADLINE_TIMER_VECTOR 0xef
+
+static u64 expire;
+static u64 delta;
+
+static void tsc_deadline_timer_isr(isr_regs_t *regs)
+{
+    apic_write(APIC_EOI, 0);
+}
+
+static void start_tsc_deadline_timer(void)
+{
+    u64 tsc;
+
+    handle_irq(TSC_DEADLINE_TIMER_VECTOR, tsc_deadline_timer_isr);
+    irq_enable();
+
+    wrmsr(MSR_IA32_TSC, delta + 1);
+    tsc = rdmsr(MSR_IA32_TSC);
+    expire = tsc + delta;
+    wrmsr(MSR_IA32_TSCDEADLINE, expire);
+    asm volatile ("nop");
+    wrmsr(MSR_IA32_TSC, 1);
+    asm volatile ("nop");
+}
+
+static int enable_tsc_deadline_timer(void)
+{
+    uint32_t lvtt;
+
+    if (cpuid(1).c & (1 << 24)) {
+        lvtt = APIC_LVT_TIMER_TSCDEADLINE | TSC_DEADLINE_TIMER_VECTOR;
+        apic_write(APIC_LVTT, lvtt);
+        start_tsc_deadline_timer();
+        return 1;
+    } else {
+        return 0;
+    }
+}
+
+static void test_tsc_deadline_timer(void)
+{
+    if (enable_tsc_deadline_timer()) {
+        printf("tsc deadline timer enabled\n");
+    } else {
+        printf("tsc deadline timer not detected, aborting\n");
+        abort();
+    }
+}
+
+int main(int argc, char **argv)
+{
+    u64 now;
+    u64 then;
+    u64 max_delta = 0;
+
+    setup_vm();
+    smp_init();
+
+    test_lapic_existence();
+
+    mask_pic_interrupts();
+
+    delta = 1UL << 32;
+
+    test_tsc_deadline_timer();
+    irq_enable();
+
+    now = rdtsc();
+    do {
+        then = now;
+        now = rdtsc();
+        if (now - then > (delta / 2)) {
+            report("delta: %lu\n", false, now - then);
+        }
+        if (now - then > max_delta) {
+            max_delta = now - then;
+        }
+    } while (now < expire + delta);
+
+    printf("max delta: %lu\n", max_delta);
+
+    return report_summary();
+}
diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index 5ecb9bba535b..b26202d32240 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -186,6 +186,10 @@  extra_params = -cpu kvm64,+rdtscp
 file = tsc_adjust.flat
 extra_params = -cpu host
 
+[tscdeadline_delay]
+file = tscdeadline_delay.flat
+extra_params = -cpu host,+tsc-deadline
+
 [xsave]
 file = xsave.flat
 arch = x86_64