On Tue, Mar 28, 2023 at 7:02 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Add test coverage to verify MSR_IA32_PRED_CMD is write-only, that it can
> be written with '0' (nop command) and '1' (IBPB command) when IBPB is
> supported by the CPU (SPEC_CTRL on Intel, IBPB on AMD), and that writing
> any other bit (1-63) triggers a #GP due to the bits/commands being
> reserved.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
I have a machine here (run-of-the-mill Skylake Xeon Gold) where
MSR_IA32_PRED_CMD does not fail for bits 1-63, so I am dropping that
bit.
Paolo
> ---
> x86/msr.c | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/x86/msr.c b/x86/msr.c
> index 97cf5987..13cb6391 100644
> --- a/x86/msr.c
> +++ b/x86/msr.c
> @@ -85,6 +85,15 @@ static void test_msr_rw(u32 msr, const char *name, unsigned long long val)
> __test_msr_rw(msr, name, val, 0);
> }
>
> +static void test_wrmsr(u32 msr, const char *name, unsigned long long val)
> +{
> + unsigned char vector = wrmsr_safe(msr, val);
> +
> + report(!vector,
> + "Expected success on WRSMR(%s, 0x%llx), got vector %d",
> + name, val, vector);
> +}
> +
> static void test_wrmsr_fault(u32 msr, const char *name, unsigned long long val)
> {
> unsigned char vector = wrmsr_safe(msr, val);
> @@ -271,6 +280,23 @@ static void test_x2apic_msrs(void)
> __test_x2apic_msrs(true);
> }
>
> +static void test_cmd_msrs(void)
> +{
> + int i;
> +
> + test_rdmsr_fault(MSR_IA32_PRED_CMD, "PRED_CMD");
> + if (this_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> + this_cpu_has(X86_FEATURE_AMD_IBPB)) {
> + test_wrmsr(MSR_IA32_PRED_CMD, "PRED_CMD", 0);
> + test_wrmsr(MSR_IA32_PRED_CMD, "PRED_CMD", PRED_CMD_IBPB);
> + } else {
> + test_wrmsr_fault(MSR_IA32_PRED_CMD, "PRED_CMD", 0);
> + test_wrmsr_fault(MSR_IA32_PRED_CMD, "PRED_CMD", PRED_CMD_IBPB);
> + }
> + for (i = 1; i < 64; i++)
> + test_wrmsr_fault(MSR_IA32_PRED_CMD, "PRED_CMD", BIT_ULL(i));
> +}
> +
> int main(int ac, char **av)
> {
> /*
> @@ -283,6 +309,7 @@ int main(int ac, char **av)
> test_misc_msrs();
> test_mce_msrs();
> test_x2apic_msrs();
> + test_cmd_msrs();
> }
>
> return report_summary();
> --
> 2.40.0.348.gf938b09366-goog
>
