[PATCH v6 17/19] i386: HV_HYPERCALL_AVAILABLE privilege bit is always needed

[Vitaly Kuznetsov]

According to TLFS, Hyper-V guest is supposed to check
HV_HYPERCALL_AVAILABLE privilege bit before accessing
HV_X64_MSR_GUEST_OS_ID/HV_X64_MSR_HYPERCALL MSRs but at least some
Windows versions ignore that. As KVM is very permissive and allows
accessing these MSRs unconditionally, no issue is observed. We may,
however, want to tighten the checks eventually. Conforming to the
spec is probably also a good idea.

Add HV_HYPERCALL_AVAILABLE to all 'leaf' features with no dependencies.

Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
 target/i386/kvm/kvm.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 2c1a77f9b00f..d81451276cd8 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -835,6 +835,8 @@ static struct {
     [HYPERV_FEAT_CRASH] = {
         .desc = "crash MSRs (hv-crash)",
         .flags = {
+            {.func = HV_CPUID_FEATURES, .reg = R_EAX,
+             .bits = HV_HYPERCALL_AVAILABLE},
             {.func = HV_CPUID_FEATURES, .reg = R_EDX,
              .bits = HV_GUEST_CRASH_MSR_AVAILABLE}
         }
@@ -843,28 +845,28 @@ static struct {
         .desc = "reset MSR (hv-reset)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_RESET_AVAILABLE}
+             .bits = HV_HYPERCALL_AVAILABLE | HV_RESET_AVAILABLE}
         }
     },
     [HYPERV_FEAT_VPINDEX] = {
         .desc = "VP_INDEX MSR (hv-vpindex)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_VP_INDEX_AVAILABLE}
+             .bits = HV_HYPERCALL_AVAILABLE | HV_VP_INDEX_AVAILABLE}
         }
     },
     [HYPERV_FEAT_RUNTIME] = {
         .desc = "VP_RUNTIME MSR (hv-runtime)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_VP_RUNTIME_AVAILABLE}
+             .bits = HV_HYPERCALL_AVAILABLE | HV_VP_RUNTIME_AVAILABLE}
         }
     },
     [HYPERV_FEAT_SYNIC] = {
         .desc = "synthetic interrupt controller (hv-synic)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_SYNIC_AVAILABLE}
+             .bits = HV_HYPERCALL_AVAILABLE | HV_SYNIC_AVAILABLE}
         }
     },
     [HYPERV_FEAT_STIMER] = {
@@ -879,7 +881,7 @@ static struct {
         .desc = "frequency MSRs (hv-frequencies)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_ACCESS_FREQUENCY_MSRS},
+             .bits = HV_HYPERCALL_AVAILABLE | HV_ACCESS_FREQUENCY_MSRS},
             {.func = HV_CPUID_FEATURES, .reg = R_EDX,
              .bits = HV_FREQUENCY_MSRS_AVAILABLE}
         }
@@ -888,7 +890,8 @@ static struct {
         .desc = "reenlightenment MSRs (hv-reenlightenment)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_ACCESS_REENLIGHTENMENTS_CONTROL}
+             .bits = HV_HYPERCALL_AVAILABLE |
+             HV_ACCESS_REENLIGHTENMENTS_CONTROL}
         }
     },
     [HYPERV_FEAT_TLBFLUSH] = {
-- 
2.30.2