* Mon Apr 28 2025 Jon Maloy <jmaloy@redhat.com> - 9.1.0-19

- kvm-target-i386-Fix-conditional-CONFIG_SYNDBG-enablement.patch [RHEL-7130] - kvm-target-i386-Exclude-hv-syndbg-from-hv-passthrough.patch [RHEL-7130] - Resolves: RHEL-7130 ([Hyper-V][RHEL9.2] Nested Hyper-V on KVM: L1 Windows VM with BIOS mode fails to boot up when using '-cpu host,hv_passthrough’ flag)
2025-04-28 15:27:51 -04:00 · 2025-04-28 15:27:51 -04:00 · 52929cc849
commit 52929cc849
parent eace179c9a
3 changed files with 221 additions and 1 deletions
--- a/kvm-target-i386-Exclude-hv-syndbg-from-hv-passthrough.patch
+++ b/kvm-target-i386-Exclude-hv-syndbg-from-hv-passthrough.patch
@ -0,0 +1,102 @@
+From 0288537593cd4452a2523b686b297dad3735f7f8 Mon Sep 17 00:00:00 2001
+From: Vitaly Kuznetsov <vkuznets@redhat.com>
+Date: Thu, 17 Apr 2025 15:30:50 +0200
+Subject: [PATCH 2/2] target/i386: Exclude 'hv-syndbg' from 'hv-passthrough'
+
+RH-Author: Vitaly Kuznetsov <vkuznets@redhat.com>
+RH-MergeRequest: 352: hyper-v: exclude 'hv-syndbg' from 'hv-passthrough' set
+RH-Jira: RHEL-7130
+RH-Acked-by: Maxim Levitsky <None>
+RH-Acked-by: Ani Sinha <anisinha@redhat.com>
+RH-Acked-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
+RH-Commit: [2/2] bf276ad5b340139f71b92e656a0c7756a55dec0b (vkuznets/qemu-kvm)
+
+Windows with Hyper-V role enabled doesn't boot with 'hv-passthrough' when
+no debugger is configured, this significantly limits the usefulness of the
+feature as there's no support for subtracting Hyper-V features from CPU
+flags at this moment (e.g. "-cpu host,hv-passthrough,-hv-syndbg" does not
+work). While this is also theoretically fixable, 'hv-syndbg' is likely
+very special and unneeded in the default set. Genuine Hyper-V doesn't seem
+to enable it either.
+
+Introduce 'skip_passthrough' flag to 'kvm_hyperv_properties' and use it as
+one-off to skip 'hv-syndbg' when enabling features in 'hv-passthrough'
+mode. Note, "-cpu host,hv-passthrough,hv-syndbg" can still be used if
+needed.
+
+As both 'hv-passthrough' and 'hv-syndbg' are debug features, the change
+should not have any effect on production environments.
+
+Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
+Link: https://lore.kernel.org/r/20240917160051.2637594-3-vkuznets@redhat.com
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+(cherry picked from commit 7d7b9c7655a26e09c800ef40373078a80e90d9f3)
+Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
+---
+ docs/system/i386/hyperv.rst | 13 +++++++++----
+ target/i386/kvm/kvm.c       |  7 +++++--
+ 2 files changed, 14 insertions(+), 6 deletions(-)
+
+diff --git a/docs/system/i386/hyperv.rst b/docs/system/i386/hyperv.rst
+index 2505dc4c86..009947e391 100644
+--- a/docs/system/i386/hyperv.rst
+++ b/docs/system/i386/hyperv.rst
+@@ -262,14 +262,19 @@ Supplementary features
+ ``hv-passthrough``
+   In some cases (e.g. during development) it may make sense to use QEMU in
+   'pass-through' mode and give Windows guests all enlightenments currently
+-  supported by KVM. This pass-through mode is enabled by "hv-passthrough" CPU
+-  flag.
+  supported by KVM.
+ 
+   Note: ``hv-passthrough`` flag only enables enlightenments which are known to QEMU
+   (have corresponding 'hv-' flag) and copies ``hv-spinlocks`` and ``hv-vendor-id``
+   values from KVM to QEMU. ``hv-passthrough`` overrides all other 'hv-' settings on
+-  the command line. Also, enabling this flag effectively prevents migration as the
+-  list of enabled enlightenments may differ between target and destination hosts.
+  the command line.
+
+  Note: ``hv-passthrough`` does not enable ``hv-syndbg`` which can prevent certain
+  Windows guests from booting when used without proper configuration. If needed,
+  ``hv-syndbg`` can be enabled additionally.
+
+  Note: ``hv-passthrough`` effectively prevents migration as the list of enabled
+  enlightenments may differ between target and destination hosts.
+ 
+ ``hv-enforce-cpuid``
+   By default, KVM allows the guest to use all currently supported Hyper-V
+diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
+index 5bf77d761f..94b678e9e3 100644
+--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
+@@ -913,6 +913,7 @@ static struct {
+         uint32_t bits;
+     } flags[2];
+     uint64_t dependencies;
+    bool skip_passthrough;
+ } kvm_hyperv_properties[] = {
+     [HYPERV_FEAT_RELAXED] = {
+         .desc = "relaxed timing (hv-relaxed)",
+@@ -1041,7 +1042,8 @@ static struct {
+             {.func = HV_CPUID_FEATURES, .reg = R_EDX,
+              .bits = HV_FEATURE_DEBUG_MSRS_AVAILABLE}
+         },
+-        .dependencies = BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED)
+        .dependencies = BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED),
+        .skip_passthrough = true,
+     },
+     [HYPERV_FEAT_MSR_BITMAP] = {
+         .desc = "enlightened MSR-Bitmap (hv-emsr-bitmap)",
+@@ -1450,7 +1452,8 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
+          * hv_build_cpuid_leaf() uses this info to build guest CPUIDs.
+          */
+         for (feat = 0; feat < ARRAY_SIZE(kvm_hyperv_properties); feat++) {
+-            if (hyperv_feature_supported(cs, feat)) {
+            if (hyperv_feature_supported(cs, feat) &&
+                !kvm_hyperv_properties[feat].skip_passthrough) {
+                 cpu->hyperv_features |= BIT(feat);
+             }
+         }
+-- 
+2.48.1
+
--- a/kvm-target-i386-Fix-conditional-CONFIG_SYNDBG-enablement.patch
+++ b/kvm-target-i386-Fix-conditional-CONFIG_SYNDBG-enablement.patch
@ -0,0 +1,108 @@
+From 26d5561f7a07c9bc6f8ea9a602c53bfa5daddd13 Mon Sep 17 00:00:00 2001
+From: Vitaly Kuznetsov <vkuznets@redhat.com>
+Date: Thu, 17 Apr 2025 15:30:42 +0200
+Subject: [PATCH 1/2] target/i386: Fix conditional CONFIG_SYNDBG enablement
+
+RH-Author: Vitaly Kuznetsov <vkuznets@redhat.com>
+RH-MergeRequest: 352: hyper-v: exclude 'hv-syndbg' from 'hv-passthrough' set
+RH-Jira: RHEL-7130
+RH-Acked-by: Maxim Levitsky <None>
+RH-Acked-by: Ani Sinha <anisinha@redhat.com>
+RH-Acked-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
+RH-Commit: [1/2] 0446b6202fb3dbae865da0dc7e08092399661f7a (vkuznets/qemu-kvm)
+
+Putting HYPERV_FEAT_SYNDBG entry under "#ifdef CONFIG_SYNDBG" in
+'kvm_hyperv_properties' array is wrong: as HYPERV_FEAT_SYNDBG is not
+the highest feature number, the result is an empty (zeroed) entry in
+the array (and not a skipped entry!). hyperv_feature_supported() is
+designed to check that all CPUID bits are set but for a zeroed
+feature in 'kvm_hyperv_properties' it returns 'true' so QEMU considers
+HYPERV_FEAT_SYNDBG as always supported, regardless of whether KVM host
+actually supports it.
+
+To fix the issue, leave HYPERV_FEAT_SYNDBG's definition in
+'kvm_hyperv_properties' array, there's nothing wrong in having it defined
+even when 'CONFIG_SYNDBG' is not set. Instead, put "hv-syndbg" CPU property
+under '#ifdef CONFIG_SYNDBG' to alter the existing behavior when the flag
+is silently skipped in !CONFIG_SYNDBG builds.
+
+Leave an 'assert' sentinel in hyperv_feature_supported() making sure there
+are no 'holes' or improperly defined features in 'kvm_hyperv_properties'.
+
+Fixes: d8701185f40c ("hw: hyperv: Initial commit for Synthetic Debugging device")
+Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
+Link: https://lore.kernel.org/r/20240917160051.2637594-2-vkuznets@redhat.com
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+(cherry picked from commit bbf3810f2c4f97bd7a1982d3e0ff0f00295b8169)
+Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
+---
+ target/i386/cpu.c     |  2 ++
+ target/i386/kvm/kvm.c | 11 +++++++----
+ 2 files changed, 9 insertions(+), 4 deletions(-)
+
+diff --git a/target/i386/cpu.c b/target/i386/cpu.c
+index a70a3aa670..0a955b1c45 100644
+--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
+@@ -8450,8 +8450,10 @@ static Property x86_cpu_properties[] = {
+                       HYPERV_FEAT_TLBFLUSH_DIRECT, 0),
+     DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
+                             hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
+#ifdef CONFIG_SYNDBG
+     DEFINE_PROP_BIT64("hv-syndbg", X86CPU, hyperv_features,
+                       HYPERV_FEAT_SYNDBG, 0),
+#endif
+     DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
+     DEFINE_PROP_BOOL("hv-enforce-cpuid", X86CPU, hyperv_enforce_cpuid, false),
+ 
+diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
+index d0329a4ed7..5bf77d761f 100644
+--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
+@@ -1035,7 +1035,6 @@ static struct {
+              .bits = HV_DEPRECATING_AEOI_RECOMMENDED}
+         }
+     },
+-#ifdef CONFIG_SYNDBG
+     [HYPERV_FEAT_SYNDBG] = {
+         .desc = "Enable synthetic kernel debugger channel (hv-syndbg)",
+         .flags = {
+@@ -1044,7 +1043,6 @@ static struct {
+         },
+         .dependencies = BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED)
+     },
+-#endif
+     [HYPERV_FEAT_MSR_BITMAP] = {
+         .desc = "enlightened MSR-Bitmap (hv-emsr-bitmap)",
+         .flags = {
+@@ -1296,6 +1294,13 @@ static bool hyperv_feature_supported(CPUState *cs, int feature)
+     uint32_t func, bits;
+     int i, reg;
+ 
+    /*
+     * kvm_hyperv_properties needs to define at least one CPUID flag which
+     * must be used to detect the feature, it's hard to say whether it is
+     * supported or not otherwise.
+     */
+    assert(kvm_hyperv_properties[feature].flags[0].func);
+
+     for (i = 0; i < ARRAY_SIZE(kvm_hyperv_properties[feature].flags); i++) {
+ 
+         func = kvm_hyperv_properties[feature].flags[i].func;
+@@ -3925,13 +3930,11 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
+                 kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_STATUS,
+                                   env->msr_hv_tsc_emulation_status);
+             }
+-#ifdef CONFIG_SYNDBG
+             if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNDBG) &&
+                 has_msr_hv_syndbg_options) {
+                 kvm_msr_entry_add(cpu, HV_X64_MSR_SYNDBG_OPTIONS,
+                                   hyperv_syndbg_query_options());
+             }
+-#endif
+         }
+         if (hyperv_feat_enabled(cpu, HYPERV_FEAT_VAPIC)) {
+             kvm_msr_entry_add(cpu, HV_X64_MSR_APIC_ASSIST_PAGE,
+-- 
+2.48.1
+
--- a/qemu-kvm.spec
+++ b/qemu-kvm.spec
@ -149,7 +149,7 @@ Obsoletes: %{name}-block-ssh <= %{epoch}:%{version}                    \
 Summary: QEMU is a machine emulator and virtualizer
 Name: qemu-kvm
 Version: 9.1.0
-Release: 18%{?rcrel}%{?dist}%{?cc_suffix}
+Release: 19%{?rcrel}%{?dist}%{?cc_suffix}
 # Epoch because we pushed a qemu-1.0 package. AIUI this can't ever be dropped
 # Epoch 15 used for RHEL 8
 # Epoch 17 used for RHEL 9 (due to release versioning offset in RHEL 8.5)
@ -545,6 +545,10 @@ Patch186: kvm-hw-virtio-Also-include-md-stubs-in-case-CONFIG_VIRTI.patch
 Patch187: kvm-virtio-mem-don-t-warn-about-THP-sizes-on-a-kernel-wi.patch
 # For RHEL-72977 - [IBM 9.7 FEAT] KVM: Enable virtio-mem support - qemu part
 Patch188: kvm-redhat-Enable-virtio-mem-on-s390x.patch
+# For RHEL-7130 - [Hyper-V][RHEL9.2] Nested Hyper-V on KVM: L1 Windows VM with BIOS mode fails to boot up when using '-cpu host,hv_passthrough’ flag
+Patch189: kvm-target-i386-Fix-conditional-CONFIG_SYNDBG-enablement.patch
+# For RHEL-7130 - [Hyper-V][RHEL9.2] Nested Hyper-V on KVM: L1 Windows VM with BIOS mode fails to boot up when using '-cpu host,hv_passthrough’ flag
+Patch190: kvm-target-i386-Exclude-hv-syndbg-from-hv-passthrough.patch

 %if %{have_clang}
 BuildRequires: clang
@ -1613,6 +1617,12 @@ useradd -r -u 107 -g qemu -G kvm -d / -s /sbin/nologin \
 %endif

 %changelog
+* Mon Apr 28 2025 Jon Maloy <jmaloy@redhat.com> - 9.1.0-19
+- kvm-target-i386-Fix-conditional-CONFIG_SYNDBG-enablement.patch [RHEL-7130]
+- kvm-target-i386-Exclude-hv-syndbg-from-hv-passthrough.patch [RHEL-7130]
+- Resolves: RHEL-7130
+  ([Hyper-V][RHEL9.2] Nested Hyper-V on KVM: L1 Windows VM with BIOS mode fails to boot up when using '-cpu host,hv_passthrough’ flag)
+
 * Mon Apr 14 2025 Jon Maloy <jmaloy@redhat.com> - 9.1.0-18
 - kvm-virtio-kconfig-memory-devices-are-PCI-only.patch [RHEL-72977]
 - kvm-hw-s390-ccw-device-Convert-to-three-phase-reset.patch [RHEL-72977]