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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1726588859; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6oaHFMscju37xAWma+lL2FhqJUsDnyK+WIoJhjUBv8c=; b=W2x44Ch5B1bBw6lfi+tZHyXwfllB6kByZHKNVum+tgTlVc+kgRnwpK9VugNiGc9NhsWL4n dqDbGxT2Iv/oqyN1Q/GsrZ+ouoXdV3tJU+bC5TJqgfyzG7NISyNeWmceygvpgQJYmMYn+O 6PDmlMm97YGBych+ETXHzRXvyG/MmZs= X-MC-Unique: X3kyOCHIOv-Ef2n6Eiivpw-1 From: Vitaly Kuznetsov To: qemu-devel@nongnu.org, Paolo Bonzini Subject: [PATCH RESEND v4 2/4] target/i386: Exclude 'hv-syndbg' from 'hv-passthrough' Date: Tue, 17 Sep 2024 18:00:49 +0200 Message-ID: <20240917160051.2637594-3-vkuznets@redhat.com> In-Reply-To: <20240917160051.2637594-1-vkuznets@redhat.com> References: <20240917160051.2637594-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1726589008648116600 Content-Type: text/plain; charset="utf-8" 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 --- 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 2505dc4c86e0..009947e39141 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. =20 Note: ``hv-passthrough`` flag only enables enlightenments which are know= n to QEMU (have corresponding 'hv-' flag) and copies ``hv-spinlocks`` and ``hv-ven= dor-id`` values from KVM to QEMU. ``hv-passthrough`` overrides all other 'hv-' se= ttings on - the command line. Also, enabling this flag effectively prevents migratio= n 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 n= eeded, + ``hv-syndbg`` can be enabled additionally. + + Note: ``hv-passthrough`` effectively prevents migration as the list of e= nabled + enlightenments may differ between target and destination hosts. =20 ``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 4009fcfd6b29..cf0449968f66 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[] =3D { [HYPERV_FEAT_RELAXED] =3D { .desc =3D "relaxed timing (hv-relaxed)", @@ -1041,7 +1042,8 @@ static struct { {.func =3D HV_CPUID_FEATURES, .reg =3D R_EDX, .bits =3D HV_FEATURE_DEBUG_MSRS_AVAILABLE} }, - .dependencies =3D BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED) + .dependencies =3D BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED= ), + .skip_passthrough =3D true, }, [HYPERV_FEAT_MSR_BITMAP] =3D { .desc =3D "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 =3D 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 |=3D BIT(feat); } } --=20 2.46.0