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[PULL 04/11] i386: expand Hyper-V features during CPU feature expansion time

Eduardo Habkost posted 11 patches 4 years, 7 months ago
[PULL 04/11] i386: expand Hyper-V features during CPU feature expansion time
Posted by Eduardo Habkost 4 years, 7 months ago 
From: Vitaly Kuznetsov <vkuznets@redhat.com>

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).

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210608120817.1325125-6-vkuznets@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target/i386/kvm/kvm_i386.h |  1 +
 target/i386/cpu.c          |  4 ++++
 target/i386/kvm/kvm-stub.c |  5 +++++
 target/i386/kvm/kvm.c      | 24 ++++++++++++++++++++----
 4 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index dc725083891..54667b35f09 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);
+bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
 
 uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 5f595a0d7e2..46befde3876 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5974,6 +5974,10 @@ 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 92f49121b8f..f6e7e4466e1 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;
 }
+
+bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
+{
+    abort();
+}
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index ef127762bca..556815db13d 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1220,13 +1220,22 @@ 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 bool hyperv_expand_features(CPUState *cs, Error **errp)
+bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
 {
-    X86CPU *cpu = X86_CPU(cs);
+    CPUState *cs = CPU(cpu);
 
     if (!hyperv_enabled(cpu))
         return true;
 
+    /*
+     * 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 true;
+
     if (cpu->hyperv_passthrough) {
         cpu->hyperv_vendor_id[0] =
             hv_cpuid_get_host(cs, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, R_EBX);
@@ -1593,8 +1602,15 @@ int kvm_arch_init_vcpu(CPUState *cs)
 
     env->apic_bus_freq = KVM_APIC_BUS_FREQUENCY;
 
-    /* Paravirtualization CPUIDs */
-    if (!hyperv_expand_features(cs, &local_err)) {
+    /*
+     * kvm_hyperv_expand_features() is called here for the second time in case
+     * KVM_CAP_SYS_HYPERV_CPUID is not supported. While we can't possibly handle
+     * 'query-cpu-model-expansion' in this case as we don't have a KVM vCPU to
+     * check which Hyper-V enlightenments are supported and which are not, we
+     * can still proceed and check/expand Hyper-V enlightenments here so legacy
+     * behavior is preserved.
+     */
+    if (!kvm_hyperv_expand_features(cpu, &local_err)) {
         error_report_err(local_err);
         return -ENOSYS;
     }
-- 
2.31.1
Re: [PULL 04/11] i386: expand Hyper-V features during CPU feature expansion time
Posted by Peter Maydell 4 years, 6 months ago 
On Tue, 13 Jul 2021 at 17:19, Eduardo Habkost <ehabkost@redhat.com> wrote:
>
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> 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).
>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Message-Id: <20210608120817.1325125-6-vkuznets@redhat.com>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Hi; Coverity reports an issue in this code (CID 1458243):

> -static bool hyperv_expand_features(CPUState *cs, Error **errp)
> +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>  {
> -    X86CPU *cpu = X86_CPU(cs);
> +    CPUState *cs = CPU(cpu);
>
>      if (!hyperv_enabled(cpu))
>          return true;
>
> +    /*
> +     * 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 true;

Here we check whether cs->kvm_state is NULL, but even if it is
NULL we can still continue execution further through the function.

Later in the function we call hv_cpuid_get_host(), which in turn
can call get_supported_hv_cpuid_legacy(), which can dereference
cs->kvm_state without checking it.

So either the check on cs->kvm_state above is unnecessary, or we
need to handle it being NULL in some way other than falling through.

Side note: this change isn't in line with our coding style, which
requires braces around the body of the if().

thanks
-- PMM
Re: [PULL 04/11] i386: expand Hyper-V features during CPU feature expansion time
Posted by Vitaly Kuznetsov 4 years, 6 months ago 
Peter Maydell <peter.maydell@linaro.org> writes:

> On Tue, 13 Jul 2021 at 17:19, Eduardo Habkost <ehabkost@redhat.com> wrote:
>>
>> From: Vitaly Kuznetsov <vkuznets@redhat.com>
>>
>> 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).
>>
>> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> Message-Id: <20210608120817.1325125-6-vkuznets@redhat.com>
>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>
> Hi; Coverity reports an issue in this code (CID 1458243):
>
>> -static bool hyperv_expand_features(CPUState *cs, Error **errp)
>> +bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>>  {
>> -    X86CPU *cpu = X86_CPU(cs);
>> +    CPUState *cs = CPU(cpu);
>>
>>      if (!hyperv_enabled(cpu))
>>          return true;
>>
>> +    /*
>> +     * 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 true;
>
> Here we check whether cs->kvm_state is NULL, but even if it is
> NULL we can still continue execution further through the function.
>
> Later in the function we call hv_cpuid_get_host(), which in turn
> can call get_supported_hv_cpuid_legacy(), which can dereference
> cs->kvm_state without checking it.

get_supported_hv_cpuid_legacy() is only called when KVM_CAP_HYPERV_CPUID
is not supported and this is not possible with
KVM_CAP_SYS_HYPERV_CPUID. Coverity, of course, can't know that.

>
> So either the check on cs->kvm_state above is unnecessary, or we
> need to handle it being NULL in some way other than falling through.

It seems an assert(cs) before calling get_supported_hv_cpuid_legacy()
(with a proper comment) should do the job.

>
> Side note: this change isn't in line with our coding style, which
> requires braces around the body of the if().

My bad, will fix.

-- 
Vitaly

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