From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 608B0C00A8F for ; Tue, 24 Oct 2023 08:59:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233991AbjJXI7o (ORCPT ); Tue, 24 Oct 2023 04:59:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53732 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233946AbjJXI7l (ORCPT ); Tue, 24 Oct 2023 04:59:41 -0400 Received: from out-190.mta1.migadu.com (out-190.mta1.migadu.com [IPv6:2001:41d0:203:375::be]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A203FAC for ; Tue, 24 Oct 2023 01:59:38 -0700 (PDT) Date: Tue, 24 Oct 2023 08:59:30 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1698137975; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=D6TYYpqy8N97kO8tVC2Cc3XTS86qRouwgud2Yw4OPK4=; b=oFd6EYkL7idjhlxEaG6UTiY53c5RjtDdeG3QcRHlcOHPEzg95lcPHSAzMzHXNHO0bq+jwH S0AjNrrfYFkVGFRIKIhvXqcpVLF/ujPhdmZwVQbJY99KGSuW/VvDTLLF9tS9aslIs6AP4R wBfV8EFFpLCr8xGx0f3ThQAbDEldEms= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Raghavendra Rao Ananta Cc: Marc Zyngier , Alexandru Elisei , James Morse , Suzuki K Poulose , Paolo Bonzini , Zenghui Yu , Shaoqin Huang , Jing Zhang , Reiji Watanabe , Colton Lewis , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v8 05/13] KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR} Message-ID: References: <20231020214053.2144305-1-rananta@google.com> <20231020214053.2144305-6-rananta@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231020214053.2144305-6-rananta@google.com> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 20, 2023 at 09:40:45PM +0000, Raghavendra Rao Ananta wrote: > For unimplemented counters, the bits in PM{C,I}NTEN{SET,CLR} and > PMOVS{SET,CLR} registers are expected to RAZ. To honor this, > explicitly implement the {get,set}_user functions for these > registers to mask out unimplemented counters for userspace reads > and writes. > > Signed-off-by: Raghavendra Rao Ananta > --- > arch/arm64/kvm/sys_regs.c | 91 ++++++++++++++++++++++++++++++++++++--- > 1 file changed, 85 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index faf97878dfbbb..2e5d497596ef8 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -987,6 +987,45 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p, > return true; > } > > +static void set_pmreg_for_valid_counters(struct kvm_vcpu *vcpu, > + u64 reg, u64 val, bool set) > +{ > + struct kvm *kvm = vcpu->kvm; > + > + mutex_lock(&kvm->arch.config_lock); > + > + /* Make the register immutable once the VM has started running */ This is a considerable change from the existing behavior and lacks justification. These registers, or rather the state that these aliases update, is mutable from the guest. I see no reason for excluding userspace from this behavior. > + if (kvm_vm_has_ran_once(kvm)) { > + mutex_unlock(&kvm->arch.config_lock); > + return; > + } > + > + val &= kvm_pmu_valid_counter_mask(vcpu); > + mutex_unlock(&kvm->arch.config_lock); I'm not entirely sold on taking the config_lock here. - If userspace is doing these ioctls in parallel then it cannot guarantee ordering in the first place, even w/ locking under the hood. Any garbage values will be discarded by KVM_REQ_RELOAD_PMU. - If the VM has already started PMCR.N is immutable, so there is no race. -- Thanks, Oliver