On Wed, Jun 29, 2022 at 7:37 PM Yang, Lixiao <lixiao.yang@xxxxxxxxx> wrote:
>
> This patch can fix the bug. I tried kvm-unit-tests vmx with your patch ten times on Ice lake and Cooper lake and the failure didn't happen. Thanks Jim!
> -----Original Message-----
> From: Jim Mattson <jmattson@xxxxxxxxxx>
> Sent: Wednesday, June 29, 2022 10:57 AM
> To: kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; Yang, Lixiao <lixiao.yang@xxxxxxxxx>; nadav.amit@xxxxxxxxx
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Subject: [kvm-unit-tests PATCH] x86: VMX: Fix the VMX-preemption timer expiration test
>
> When the VMX-preemption timer fires between the test for
> "vmx_get_test_stage() == 0" and the subsequent rdtsc instruction, the final VM-entry to finish the guest will inadvertently update vmx_preemption_timer_expiry_finish.
>
> Move the code to finish the guest until after the calculations involving vmx_preemption_timer_expiry_finish are done, so that it doesn't matter if vmx_preemption_timer_expiry_finish is clobbered.
>
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Reported-by: Nadav Amit <nadav.amit@xxxxxxxxx>
Tested-by: Lixiao Yang <lixiao.yang@xxxxxxxxx>
> Fixes: b49a1a6d4e23 ("x86: VMX: Add a VMX-preemption timer expiration test")
> ---
> x86/vmx_tests.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c index 4d581e7085ea..8a1393668d93 100644
> --- a/x86/vmx_tests.c
> +++ b/x86/vmx_tests.c
> @@ -9194,16 +9194,16 @@ static void vmx_preemption_timer_expiry_test(void)
> reason = (u32)vmcs_read(EXI_REASON);
> TEST_ASSERT(reason == VMX_PREEMPT);
>
> - vmcs_clear_bits(PIN_CONTROLS, PIN_PREEMPT);
> - vmx_set_test_stage(1);
> - enter_guest();
> -
> tsc_deadline = ((vmx_preemption_timer_expiry_start >> misc.pt_bit) <<
> misc.pt_bit) + (preemption_timer_value << misc.pt_bit);
>
> report(vmx_preemption_timer_expiry_finish < tsc_deadline,
> "Last stored guest TSC (%lu) < TSC deadline (%lu)",
> vmx_preemption_timer_expiry_finish, tsc_deadline);
> +
> + vmcs_clear_bits(PIN_CONTROLS, PIN_PREEMPT);
> + vmx_set_test_stage(1);
> + enter_guest();
> }
>
> static void vmx_db_test_guest(void)
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>
