From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (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 930662B9B0 for ; Mon, 26 Aug 2024 18:31:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724697100; cv=none; b=fZbCJQA4kJsY7v8oHTYeJaDF+sOo2Bs2X694IM2GCJvEZPbYdp1JZ1TMHrwaXyPiP+cQ6KEaL5O07L4bTyWsCM2VWXVCb2/7grPs3zcvMxamFexp4CxP4fq2wRwA/Lzx1kMHLWGKda3sa/3ABzpRjH5Fk3OaxbX3d3QkcYHdlOE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724697100; c=relaxed/simple; bh=mLy1vgHmE/jdzt3VgHm2OHzYuPjcX8WTmOb+o6YMWp8=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Cg3Y30yQQ4XempEcU+Ssc34Ent9MOUNe0SlAvP1QBGIgAEiv8EaK5+YgUgnm15Gh+qbtRJOFyUyaRYPgzJBsiykuR2YtcDHA5nuv2Ti/qFt4M2WYMc7ZaPG3Rlt3DtKHJYdU596byQnf7AbmsUPJ0TELBJQQVaP1ryRjEzKG4Go= 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=DjHeUdV9; arc=none smtp.client-ip=209.85.128.201 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="DjHeUdV9" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-6af8f7a30dbso100803307b3.2 for ; Mon, 26 Aug 2024 11:31:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1724697097; x=1725301897; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=oYs4/XGahzBT4qBo/4ZIs3WQHA47MKX2vPkz30h9+7Q=; b=DjHeUdV9FoT3RQpj4W+uwfk/mC4nFHRZu3MSPfjKvYp+DWkV4YLCYL9GB1QsxOlcmG +HI0UsVVvBarrOKwtsgZcYbIE7DmCOZ8gRPlt0sKlHOQID+5kxljDV5famgWcVML8JLr f6KhvcM4NIHzryBrvclanMzx3NPmBuNo6zzyaIjaxMZdnf6lZ88rkjh+koKMyZjeQWWr b0M6O0DK4HXPkMuJPlFIvj3iG9H3Ed/tLup/CXjjDY34uK8siz5VCdLArbbZaFp+a2io JognSKEHd8T0eFn4DPakVZUp5lCfp/QUF5qxxRiqnEih2X0SCeCTjBzbA5Hwza7lr0Lz E7zA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1724697097; x=1725301897; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=oYs4/XGahzBT4qBo/4ZIs3WQHA47MKX2vPkz30h9+7Q=; b=N4TSHbUzNfcC7loneOtDmHxw+wubWd+NOP5TaZR3PNUDXbTplWPuESpiaQF0zvkg4T iJMDcAU/K192NewI03XXJkN5N9eeY/wZlmMgz3t2JnVo5YYFNVDbfgI/1WJ+botoMXwd AyjUzoqmjx0oy1m4OpQe0t10hZArG0xrDG/wAyjEWwP/uPsavxYhc5/NzkBM5bTH6/4w nRn12zKD1q3F5b+z+YVoJXtwz3q9E0ax8AcLxrOPfZWWeFMAVFVWmKvfhA56GsfmeNdk jjDQbu9c0YCtn7DmjpV5qtCdLx8Uzn0pn5u72Y2PMdsg7fCEbbbd0OL0F43viKShQY9c G1Nw== X-Forwarded-Encrypted: i=1; AJvYcCX5bZEG9YO0cUNNsbHD9E7cqz1MZWDph0PlmcxeYujS5YJswMWmFb8Ec6d4YhN1DUEOZOD0phPxiqMam2U=@vger.kernel.org X-Gm-Message-State: AOJu0YwGOlbhmc6wM2B8jldGaHPObk8u+M0U8DgZLWIZ80UByxBTMu0U nhES3M1f0wnfS2bqPQMdBSC1M70tKg09GicK/fZECU3rCwhYZ8zC7VbDJAJAYfl5TIf6heom7aH CVg== X-Google-Smtp-Source: AGHT+IEZVzpeG0G0tHxTLIM7OwZkYTrzg2NvTEAhQlUNRbdJi8Gn+6CbL5ryMGABFu9BH/rPP+zE67W44Ts= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:3617:0:b0:e13:c772:5c18 with SMTP id 3f1490d57ef6-e17a866a769mr18546276.12.1724697097393; Mon, 26 Aug 2024 11:31:37 -0700 (PDT) Date: Mon, 26 Aug 2024 11:31:36 -0700 In-Reply-To: <5fe11dfb-2a33-4b52-8181-c82bc326b968@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240808062937.1149-1-ravi.bangoria@amd.com> <20240808062937.1149-5-ravi.bangoria@amd.com> <372d5a95-bce5-4c5c-8c74-6b4cc5ab6943@amd.com> <5fe11dfb-2a33-4b52-8181-c82bc326b968@amd.com> Message-ID: Subject: Re: [PATCH v4 4/4] KVM: SVM: Add Bus Lock Detect support From: Sean Christopherson To: Ravi Bangoria Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, pbonzini@redhat.com, thomas.lendacky@amd.com, jmattson@google.com, hpa@zytor.com, rmk+kernel@armlinux.org.uk, peterz@infradead.org, james.morse@arm.com, lukas.bulwahn@gmail.com, arjan@linux.intel.com, j.granados@samsung.com, sibs@chinatelecom.cn, nik.borisov@suse.com, michael.roth@amd.com, nikunj.dadhania@amd.com, babu.moger@amd.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, santosh.shukla@amd.com, ananth.narayan@amd.com, sandipan.das@amd.com, manali.shukla@amd.com Content-Type: text/plain; charset="us-ascii" On Wed, Aug 21, 2024, Ravi Bangoria wrote: > On 21-Aug-24 11:06 AM, Ravi Bangoria wrote: > >>> @@ -3158,6 +3159,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) > >>> if (data & DEBUGCTL_RESERVED_BITS) > >> > >> Not your code, but why does DEBUGCTL_RESERVED_BITS = ~0x3f!?!? That means the > >> introduction of the below check, which is architecturally correct, has the > >> potential to break guests. *sigh* > >> > >> I doubt it will cause a problem, but it's something to look out for. > > This dates back to 2008: https://git.kernel.org/torvalds/c/24e09cbf480a7 > > > > The legacy definition[1] of DEBUGCTL MSR is: > > > > 5:2 PB: performance monitor pin control. Read-write. Reset: 0h. > > This field does not control any hardware. Uh, what? So the CPU provided 4 bits of scratch space? Or is that saying that 5:2 controlled some perfmon stuff on older CPUs, but that Zen deprecated those bits? > > 1 BTF. Read-write. Reset: 0. 1=Enable branch single step. > > 0 LBR. Read-write. Reset: 0. 1=Enable last branch record. > > > > [1]: https://bugzilla.kernel.org/attachment.cgi?id=287389 > > How about adding cpu_feature_enabled() check: That doesn't fix anything, KVM will still break, just on a smaller set of CPUs. The only way to avoid breaking guests is to ignore bits 5:2, though we could quirk that so that userspace can effectively enable what is now the architectural behavior. Though I'm very tempted to just add a prep patch to disallow setting bits 5:2 and see if anyone complains. If they do, then we can add a quirk. And if no one complains, yay.