Re: [PATCH 4/4] KVM: selftests: Test access to XMM fast hypercalls

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Siddharth Chandrasekaran <sidcha@amazon.de> writes:

> On Fri, Jul 30, 2021 at 02:26:25PM +0200, Vitaly Kuznetsov wrote:
>> HYPERV_CPUID_FEATURES.EDX and an 'XMM fast' hypercall is issued.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  .../selftests/kvm/include/x86_64/hyperv.h     |  5 ++-
>>  .../selftests/kvm/x86_64/hyperv_features.c    | 41 +++++++++++++++++--
>>  2 files changed, 42 insertions(+), 4 deletions(-)
>> 
>> diff --git a/tools/testing/selftests/kvm/include/x86_64/hyperv.h b/tools/testing/selftests/kvm/include/x86_64/hyperv.h
>> index 412eaee7884a..b66910702c0a 100644
>> --- a/tools/testing/selftests/kvm/include/x86_64/hyperv.h
>> +++ b/tools/testing/selftests/kvm/include/x86_64/hyperv.h
>> @@ -117,7 +117,7 @@
>>  #define HV_X64_GUEST_DEBUGGING_AVAILABLE               BIT(1)
>>  #define HV_X64_PERF_MONITOR_AVAILABLE                  BIT(2)
>>  #define HV_X64_CPU_DYNAMIC_PARTITIONING_AVAILABLE      BIT(3)
>> -#define HV_X64_HYPERCALL_PARAMS_XMM_AVAILABLE          BIT(4)
>> +#define HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE           BIT(4)
>>  #define HV_X64_GUEST_IDLE_STATE_AVAILABLE              BIT(5)
>>  #define HV_FEATURE_FREQUENCY_MSRS_AVAILABLE            BIT(8)
>>  #define HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE           BIT(10)
>> @@ -182,4 +182,7 @@
>>  #define HV_STATUS_INVALID_CONNECTION_ID                18
>>  #define HV_STATUS_INSUFFICIENT_BUFFERS         19
>> 
>> +/* hypercall options */
>> +#define HV_HYPERCALL_FAST_BIT          BIT(16)
>> +
>>  #endif /* !SELFTEST_KVM_HYPERV_H */
>> diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_features.c b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
>> index af27c7e829c1..91d88aaa9899 100644
>> --- a/tools/testing/selftests/kvm/x86_64/hyperv_features.c
>> +++ b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
>> @@ -47,6 +47,7 @@ static void do_wrmsr(u32 idx, u64 val)
>>  }
>> 
>>  static int nr_gp;
>> +static int nr_ud;
>> 
>>  static inline u64 hypercall(u64 control, vm_vaddr_t input_address,
>>                             vm_vaddr_t output_address)
>> @@ -80,6 +81,12 @@ static void guest_gp_handler(struct ex_regs *regs)
>>                 regs->rip = (uint64_t)&wrmsr_end;
>>  }
>> 
>> +static void guest_ud_handler(struct ex_regs *regs)
>> +{
>> +       nr_ud++;
>> +       regs->rip += 3;
>> +}
>> +
>>  struct msr_data {
>>         uint32_t idx;
>>         bool available;
>> @@ -90,6 +97,7 @@ struct msr_data {
>>  struct hcall_data {
>>         uint64_t control;
>>         uint64_t expect;
>> +       bool ud_expected;
>>  };
>> 
>>  static void guest_msr(struct msr_data *msr)
>> @@ -117,13 +125,26 @@ static void guest_msr(struct msr_data *msr)
>>  static void guest_hcall(vm_vaddr_t pgs_gpa, struct hcall_data *hcall)
>>  {
>>         int i = 0;
>> +       u64 res, input, output;
>> 
>>         wrmsr(HV_X64_MSR_GUEST_OS_ID, LINUX_OS_ID);
>>         wrmsr(HV_X64_MSR_HYPERCALL, pgs_gpa);
>> 
>>         while (hcall->control) {
>> -               GUEST_ASSERT(hypercall(hcall->control, pgs_gpa,
>> -                                      pgs_gpa + 4096) == hcall->expect);
>> +               nr_ud = 0;
>> +               if (!(hcall->control & HV_HYPERCALL_FAST_BIT)) {
>> +                       input = pgs_gpa;
>> +                       output = pgs_gpa + 4096;
>> +               } else {
>> +                       input = output = 0;
>> +               }
>> +
>> +               res = hypercall(hcall->control, input, output);
>> +               if (hcall->ud_expected)
>> +                       GUEST_ASSERT(nr_ud == 1);
>
> Should we also do WRITE_ONCE(nr_ur, 0) here?

It could probably make sense to replace 'nr_ud = 0' above with this so
compiler doesn't screw us up one day..

> or perhaps pass the the
> expected value of nr_ud + 1 in hcall->ud_expected from caller and do,
>
>     if (hcall->ud_expected)
>         GUEST_ASSERT(nr_ud == hcall->ud_expected);
>
> This way there can be other test that can also expect a UD.

My idea was that we don't really need to count #UDs for now, just
checking the fact that it happened is OK so I reset nr_ud before doing
the hypercall and check it after. It is possible to add more tests with
'ud_expected' this way.

>
>> +               else
>> +                       GUEST_ASSERT(res == hcall->expect);
>> +
>>                 GUEST_SYNC(i++);
>>         }
>> 
>> @@ -552,8 +573,18 @@ static void guest_test_hcalls_access(struct kvm_vm *vm, struct hcall_data *hcall
>>                         recomm.ebx = 0xfff;
>>                         hcall->expect = HV_STATUS_SUCCESS;
>>                         break;
>> -
>>                 case 17:
>> +                       /* XMM fast hypercall */
>> +                       hcall->control = HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE | HV_HYPERCALL_FAST_BIT;
>> +                       hcall->ud_expected = true;
>> +                       break;
>> +               case 18:
>> +                       feat.edx |= HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE;
>> +                       hcall->ud_expected = false;
>> +                       hcall->expect = HV_STATUS_SUCCESS;
>> +                       break;
>> +
>> +               case 19:
>>                         /* END */
>>                         hcall->control = 0;
>>                         break;
>> @@ -625,6 +656,10 @@ int main(void)
>>         /* Test hypercalls */
>>         vm = vm_create_default(VCPU_ID, 0, guest_hcall);
>> 
>> +       vm_init_descriptor_tables(vm);
>> +       vcpu_init_descriptor_tables(vm, VCPU_ID);
>> +       vm_install_exception_handler(vm, UD_VECTOR, guest_ud_handler);
>> +
>>         /* Hypercall input/output */
>>         hcall_page = vm_vaddr_alloc_pages(vm, 2);
>>         memset(addr_gva2hva(vm, hcall_page), 0x0, 2 * getpagesize());
>> --
>> 2.31.1
>> 
>
>
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-- 
Vitaly