From patchwork Mon Mar 3 23:57:00 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13999620 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 375B0F9E6 for ; Mon, 3 Mar 2025 23:57:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741046224; cv=none; b=XPR9dSknqXaI6U85/Bh/x8WW9RjEWlpT0VYbsAqDohsutPLqwrEsc/AdDJiHspaGB3VnGwK6rTycrADPHP/8bUYJkodgOo5wtv7pni6AJIaWGNmKw5VgCLa8Iom9UZ2wh0JCOAuHv2HHAlUwivDJWt57Vvf7EVIYXgFbIisTAJY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741046224; c=relaxed/simple; bh=cybyLF+6a0xFOLpaO7HAkjnx8B+DEcCnYsdTti7tMtQ=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=XGIBSnP7IgclqKUcEFOV8xdvKq0i19AkxLTBE+1uDijlo1RY3QORKJhIiALwYeUwWdAUsAJ/7+wiIR8llDJbX4lUozxu4F6OAnonUojS75jXrbDI7AjGDayGFsBgbdv95yCo5C5tbZwUOuaU4/NHmu5bmvZtlGaD5bnOLhPCaRs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=MuOwASM5; arc=none smtp.client-ip=209.85.214.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="MuOwASM5" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-22379c2e96aso14909945ad.1 for ; Mon, 03 Mar 2025 15:57:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1741046222; x=1741651022; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=gd+RfLlKh5tESoQa3l8PmuvkGSAlK2XxIUJYV0fVaBg=; b=MuOwASM51tGoiiDzoiaNsI7YoNml4FrOt8Dm5mtoQEwKzzSOcxHdlC7Tz+E6A9VZxf Cgx8IPIjgtsu7cXaZMVdLbZ6qy+Ama5R+5qtF9Gi+SLOmkX+MXIlWJiUYyIfYgojw5zI XC4L2jzE378HkgtKdkxwfmyVTF5vCiCWcWWNYob8SVRbyRu2J6Jta8+pJ92R5r0T+g3F KzhToZrz4PPBo872VhidhQ0djB4ZPs9DreRlx4AdiMfkKfJAboQxIjg0hzGd64mcHiAf g1RRqqtmhZM2PDgq7PtrL73FnNEW8VkhS4AO71DYSqFuRClBvCOxbYchSJ9FISle1+5R UqHA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741046222; x=1741651022; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=gd+RfLlKh5tESoQa3l8PmuvkGSAlK2XxIUJYV0fVaBg=; b=JlOKVULGWq0ghrrvtZlaqRoHOWjPj92zRiz8R6k3XvFZ7eW0BerWQz1X4iwktghc+3 HzGvouwFKptfwvcDElp6QZycL079xK/k4MBE3zuxsGI+d7IQ3ndLPwvZ+UrxRzUNNf1+ zBSZAtvY+wKzWx7EPP4dXDNQOZ0vsl6htK4pSCGQd6i4Wfuc9wj3/l0/9e6fFvkWHD0j HrVpXsybaqCrvEvf3tKdFGBg7Ra5hRo5C1ZrcUmj/IAyqYQufGz6UStSt2SWOC0hlE6D xAcEaTPHl7Gna/pW7AEZe6ORACGor8oerMFN3X1LL13keujAf1aowc7lwI7d7HKwYBoO 15KQ== X-Gm-Message-State: AOJu0YxMQ0CQqKC/tNTyBgv5U8hhh0jQFUvV2fFJAltY1uifg1Y6/yh5 CMXFn5W79vwNusDkTDbFqC6gI6Jn2Psf4ESUuOhvHqBahJUpmjEiwtwoeRmGdmT3Fv2YTfPx4j5 QGw== X-Google-Smtp-Source: AGHT+IGX5wRTQnobJEKkoY5D6cUlZvAzQBSWp/HIXHWLswgh1Uyt2skI71q+ZOuax94kvBsik5c1VZXC7c0= X-Received: from pfhg4.prod.google.com ([2002:a62:e304:0:b0:730:85dc:cebb]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:1a8f:b0:736:4830:68a6 with SMTP id d2e1a72fcca58-7364830691bmr10633992b3a.4.1741046222428; Mon, 03 Mar 2025 15:57:02 -0800 (PST) Date: Mon, 3 Mar 2025 15:57:00 -0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Message-ID: Subject: QEMU's Hyper-V HV_X64_MSR_EOM is broken with split IRQCHIP From: Sean Christopherson To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Peter Xu FYI, QEMU's Hyper-V emulation of HV_X64_MSR_EOM has been broken since QEMU commit c82d9d43ed ("KVM: Kick resamplefd for split kernel irqchip"), as nothing in KVM will forward the EOM notification to userspace. I have no idea if anything in QEMU besides hyperv_testdev.c cares. The bug is reproducible by running the hyperv_connections KVM-Unit-Test with a split IRQCHIP. Hacking QEMU and KVM (see KVM commit 654f1f13ea56 ("kvm: Check irqchip mode before assign irqfd") as below gets the test to pass. Assuming that's not a palatable solution, the other options I can think of would be for QEMU to intercept HV_X64_MSR_EOM when using a split IRQCHIP, or to modify KVM to do KVM_EXIT_HYPERV_SYNIC on writes to HV_X64_MSR_EOM with a split IRQCHIP. diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index c65b790433..820bc1692e 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -2261,10 +2261,9 @@ static int kvm_irqchip_assign_irqfd(KVMState *s, EventNotifier *event, * the INTx slow path). */ kvm_resample_fd_insert(virq, resample); - } else { - irqfd.flags |= KVM_IRQFD_FLAG_RESAMPLE; - irqfd.resamplefd = rfd; } + irqfd.flags |= KVM_IRQFD_FLAG_RESAMPLE; + irqfd.resamplefd = rfd; } else if (!assign) { if (kvm_irqchip_is_split()) { kvm_resample_fd_remove(virq); diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c index 63f66c51975a..0bf85f89eb27 100644 --- a/arch/x86/kvm/irq.c +++ b/arch/x86/kvm/irq.c @@ -166,9 +166,7 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu) bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args) { - bool resample = args->flags & KVM_IRQFD_FLAG_RESAMPLE; - - return resample ? irqchip_kernel(kvm) : irqchip_in_kernel(kvm); + return irqchip_in_kernel(kvm); } bool kvm_arch_irqchip_in_kernel(struct kvm *kvm)