On Wed, Sep 18, 2019 at 03:23:54PM -0700, Marc Orr wrote:
...
> +static void atomic_switch_msr_limit_test_guest(void)
> +{
> + vmcall();
I finally dug into the weird double-enter_guest(). Rather than re-enter
the guest to cleanup, just remove this vmcall() so that the first VM-Enter
invokes hypercall() with HYPERCALL_VMEXIT to set guest_finished.
enter_guest() will verify VM-Enter succeeded, and the guest_finished check
verifies the guest did a VMCALL. I don't see any added value in an extra
VMCALL.
> +}
> +
> +static void populate_msr_list(struct vmx_msr_entry *msr_list,
> + size_t byte_capacity, int count)
> +{
> + int i;
> +
> + for (i = 0; i < count; i++) {
> + msr_list[i].index = MSR_IA32_TSC;
> + msr_list[i].reserved = 0;
> + msr_list[i].value = 0x1234567890abcdef;
> + }
> +
> + memset(msr_list + count, 0xff,
> + byte_capacity - count * sizeof(*msr_list));
> +}
> +
> +static int max_msr_list_size(void)
> +{
> + u32 vmx_misc = rdmsr(MSR_IA32_VMX_MISC);
> + u32 factor = ((vmx_misc & GENMASK(27, 25)) >> 25) + 1;
> +
> + return factor * 512;
> +}
> +
> +static void atomic_switch_msrs_test(int count)
> +{
> + struct vmx_msr_entry *vm_enter_load;
> + struct vmx_msr_entry *vm_exit_load;
> + struct vmx_msr_entry *vm_exit_store;
> + int max_allowed = max_msr_list_size();
> + int byte_capacity = 1ul << (msr_list_page_order + PAGE_SHIFT);
> + /* KVM signals VM-Abort if an exit MSR list exceeds the max size. */
> + int exit_count = MIN(count, max_allowed);
> +
> + /*
> + * Check for the IA32_TSC MSR,
> + * available with the "TSC flag" and used to populate the MSR lists.
> + */
> + if (!(cpuid(1).d & (1 << 4))) {
> + report_skip(__func__);
> + return;
> + }
> +
> + /* Set L2 guest. */
> + test_set_guest(atomic_switch_msr_limit_test_guest);
> +
> + /* Setup atomic MSR switch lists. */
> + vm_enter_load = alloc_pages(msr_list_page_order);
> + vm_exit_load = alloc_pages(msr_list_page_order);
> + vm_exit_store = alloc_pages(msr_list_page_order);
> +
> + vmcs_write(ENTER_MSR_LD_ADDR, (u64)vm_enter_load);
> + vmcs_write(EXIT_MSR_LD_ADDR, (u64)vm_exit_load);
> + vmcs_write(EXIT_MSR_ST_ADDR, (u64)vm_exit_store);
> +
> + /*
> + * VM-Enter should succeed up to the max number of MSRs per list, and
> + * should not consume junk beyond the last entry.
> + */
> + populate_msr_list(vm_enter_load, byte_capacity, count);
> + populate_msr_list(vm_exit_load, byte_capacity, exit_count);
> + populate_msr_list(vm_exit_store, byte_capacity, exit_count);
> +
> + vmcs_write(ENT_MSR_LD_CNT, count);
> + vmcs_write(EXI_MSR_LD_CNT, exit_count);
> + vmcs_write(EXI_MSR_ST_CNT, exit_count);
> +
> + if (count <= max_allowed) {
> + enter_guest();
> + skip_exit_vmcall();
If vmcall() is removed, this skip and the one in the else{} can be dropped.
> + } else {
> + u32 exit_reason;
> + u32 exit_reason_want;
> + u32 exit_qual;
> +
> + enter_guest_with_invalid_guest_state();
> +
> + exit_reason = vmcs_read(EXI_REASON);
> + exit_reason_want = VMX_FAIL_MSR | VMX_ENTRY_FAILURE;
> + report("exit_reason, %u, is %u.",
> + exit_reason == exit_reason_want, exit_reason,
> + exit_reason_want);
> +
> + exit_qual = vmcs_read(EXI_QUALIFICATION);
> + report("exit_qual, %u, is %u.", exit_qual == max_allowed + 1,
> + exit_qual, max_allowed + 1);
> +
> + /*
> + * Re-enter the guest with valid counts
> + * and proceed past the single vmcall instruction.
> + */
Nit: "Re-enter the guest" should either be "Retry VM-Enter" or simply
"Enter". The reason this code exists is that we never actually
entered the guest :-)
E.g. if you drop the vmcall():
/* Enter the guest (with valid counts) to set guest_finished. */
> + vmcs_write(ENT_MSR_LD_CNT, 0);
> + vmcs_write(EXI_MSR_LD_CNT, 0);
> + vmcs_write(EXI_MSR_ST_CNT, 0);
> + enter_guest();
> + skip_exit_vmcall();
> + }
> +
> + /* Cleanup. */
> + enter_guest();
> + skip_exit_vmcall();
> + free_pages_by_order(vm_enter_load, msr_list_page_order);
> + free_pages_by_order(vm_exit_load, msr_list_page_order);
> + free_pages_by_order(vm_exit_store, msr_list_page_order);
> +}
> +
> +static void atomic_switch_max_msrs_test(void)
> +{
> + atomic_switch_msrs_test(max_msr_list_size());
> +}
> +
> +static void atomic_switch_overflow_msrs_test(void)
> +{
> + atomic_switch_msrs_test(max_msr_list_size() + 1);
> +}
>
> #define TEST(name) { #name, .v2 = name }
>
> @@ -8660,5 +8791,8 @@ struct vmx_test vmx_tests[] = {
> TEST(ept_access_test_paddr_read_execute_ad_enabled),
> TEST(ept_access_test_paddr_not_present_page_fault),
> TEST(ept_access_test_force_2m_page),
> + /* Atomic MSR switch tests. */
> + TEST(atomic_switch_max_msrs_test),
> + TEST(atomic_switch_overflow_msrs_test),
> { NULL, NULL, NULL, NULL, NULL, {0} },
> };
> --
> 2.23.0.237.gc6a4ce50a0-goog
>
