diff mbox series

[v7,7/9] i386: HV_HYPERCALL_AVAILABLE privilege bit is always needed

Message ID 20210603114835.847451-8-vkuznets@redhat.com (mailing list archive)
State New, archived
Headers show
Series i386: KVM: expand Hyper-V features early | expand

Commit Message

Vitaly Kuznetsov June 3, 2021, 11:48 a.m. UTC 
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.

Enable HV_HYPERCALL_AVAILABLE bit unconditionally.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 target/i386/kvm/kvm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Comments

Eduardo Habkost June 3, 2021, 10:43 p.m. UTC | #1 
On Thu, Jun 03, 2021 at 01:48:33PM +0200, Vitaly Kuznetsov wrote:
> 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.
> 
> Enable HV_HYPERCALL_AVAILABLE bit unconditionally.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
diff mbox series

Patch

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 93f9b5a457d5..a3897d4d8788 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -810,8 +810,6 @@  static struct {
     [HYPERV_FEAT_RELAXED] = {
         .desc = "relaxed timing (hv-relaxed)",
         .flags = {
-            {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_HYPERCALL_AVAILABLE},
             {.func = HV_CPUID_ENLIGHTMENT_INFO, .reg = R_EAX,
              .bits = HV_RELAXED_TIMING_RECOMMENDED}
         }
@@ -820,7 +818,7 @@  static struct {
         .desc = "virtual APIC (hv-vapic)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_HYPERCALL_AVAILABLE | HV_APIC_ACCESS_AVAILABLE},
+             .bits = HV_APIC_ACCESS_AVAILABLE},
             {.func = HV_CPUID_ENLIGHTMENT_INFO, .reg = R_EAX,
              .bits = HV_APIC_ACCESS_RECOMMENDED}
         }
@@ -829,8 +827,7 @@  static struct {
         .desc = "clocksources (hv-time)",
         .flags = {
             {.func = HV_CPUID_FEATURES, .reg = R_EAX,
-             .bits = HV_HYPERCALL_AVAILABLE | HV_TIME_REF_COUNT_AVAILABLE |
-             HV_REFERENCE_TSC_AVAILABLE}
+             .bits = HV_TIME_REF_COUNT_AVAILABLE | HV_REFERENCE_TSC_AVAILABLE}
         }
     },
     [HYPERV_FEAT_CRASH] = {
@@ -1343,6 +1340,9 @@  static int hyperv_fill_cpuids(CPUState *cs,
     c->ebx = hv_build_cpuid_leaf(cs, HV_CPUID_FEATURES, R_EBX);
     c->edx = hv_build_cpuid_leaf(cs, HV_CPUID_FEATURES, R_EDX);
 
+    /* Unconditionally required with any Hyper-V enlightenment */
+    c->eax |= HV_HYPERCALL_AVAILABLE;
+
     /* Not exposed by KVM but needed to make CPU hotplug in Windows work */
     c->edx |= HV_CPU_DYNAMIC_PARTITIONING_AVAILABLE;