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Re: [PATCH v6 15/19] i386: expand Hyper-V features during CPU feature ex
From: |
Vitaly Kuznetsov |
Subject: |
Re: [PATCH v6 15/19] i386: expand Hyper-V features during CPU feature expansion time |
Date: |
Mon, 24 May 2021 14:13:09 +0200 |
Eduardo Habkost <ehabkost@redhat.com> writes:
> On Thu, Apr 22, 2021 at 06:11:26PM +0200, Vitaly Kuznetsov wrote:
>> To make Hyper-V features appear in e.g. QMP query-cpu-model-expansion we
>> need to expand and set the corresponding CPUID leaves early. Modify
>> x86_cpu_get_supported_feature_word() to call newly intoduced Hyper-V
>> specific kvm_hv_get_supported_cpuid() instead of
>> kvm_arch_get_supported_cpuid(). We can't use kvm_arch_get_supported_cpuid()
>> as Hyper-V specific CPUID leaves intersect with KVM's.
>>
>> Note, early expansion will only happen when KVM supports system wide
>> KVM_GET_SUPPORTED_HV_CPUID ioctl (KVM_CAP_SYS_HYPERV_CPUID).
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>> target/i386/cpu.c | 4 ++++
>> target/i386/kvm/kvm-stub.c | 5 +++++
>> target/i386/kvm/kvm.c | 15 ++++++++++++---
>> target/i386/kvm/kvm_i386.h | 1 +
>> 4 files changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index d72b8760e7a3..18b57f3d8b9c 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -6514,6 +6514,10 @@ static void x86_cpu_expand_features(X86CPU *cpu,
>> Error **errp)
>> if (env->cpuid_xlevel2 == UINT32_MAX) {
>> env->cpuid_xlevel2 = env->cpuid_min_xlevel2;
>> }
>> +
>> + if (kvm_enabled()) {
>> + kvm_hyperv_expand_features(cpu, errp);
>> + }
>> }
>>
>> /*
>> diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
>> index 92f49121b8fa..7f175faa3abd 100644
>> --- a/target/i386/kvm/kvm-stub.c
>> +++ b/target/i386/kvm/kvm-stub.c
>> @@ -39,3 +39,8 @@ bool kvm_hv_vpindex_settable(void)
>> {
>> return false;
>> }
>> +
>> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>> +{
>> + return;
>
> Maybe we should make it abort()? This function should never be
> called if KVM is disabled.
>
Sure, can do that.
>> +}
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index a42263b24fca..d5551c4ab5cf 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -1216,13 +1216,22 @@ static uint32_t hv_build_cpuid_leaf(CPUState *cs,
>> uint32_t func, int reg)
>> * of 'hv_passthrough' mode and fills the environment with all supported
>> * Hyper-V features.
>> */
>> -static void hyperv_expand_features(CPUState *cs, Error **errp)
>> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>> {
>> - X86CPU *cpu = X86_CPU(cs);
>> + CPUState *cs = CPU(cpu);
>>
>> if (!hyperv_enabled(cpu))
>> return;
>>
>> + /*
>> + * When kvm_hyperv_expand_features is called at CPU feature expansion
>> + * time per-CPU kvm_state is not available yet so we can only proceed
>> + * when KVM_CAP_SYS_HYPERV_CPUID is supported.
>> + */
>> + if (!cs->kvm_state &&
>> + !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID))
>> + return;
>> +
>> if (cpu->hyperv_passthrough) {
>> cpu->hyperv_vendor_id[0] =
>> hv_cpuid_get_host(cs, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, R_EBX);
>> @@ -1556,7 +1565,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>> env->apic_bus_freq = KVM_APIC_BUS_FREQUENCY;
>>
>> /* Paravirtualization CPUIDs */
>> - hyperv_expand_features(cs, &local_err);
>> + kvm_hyperv_expand_features(cpu, &local_err);
>
> Do we still need to call the function again here?
>
> If the first expansion isn't expanding everything, I'm afraid
> this second call will hide bugs in query-cpu-model-expansion.
>
The first expansion will do nothing if KVM_CAP_SYS_HYPERV_CPUID is not
supported, calling it here allows us to proceed. The series makes
'query-cpu-model-expansion' output correct only with
KVM_CAP_SYS_HYPERV_CPUID, without it we don't seem to be able to do much
(unless we decide to create a 'scratch' CPU or something like that).
>
>> if (local_err) {
>> error_report_err(local_err);
>> return -ENOSYS;
>> diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
>> index dc725083891c..f1176491051d 100644
>> --- a/target/i386/kvm/kvm_i386.h
>> +++ b/target/i386/kvm/kvm_i386.h
>> @@ -47,6 +47,7 @@ bool kvm_has_x2apic_api(void);
>> bool kvm_has_waitpkg(void);
>>
>> bool kvm_hv_vpindex_settable(void);
>> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
>>
>> uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
>>
>> --
>> 2.30.2
>>
--
Vitaly