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 X-Spam-Level: X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08D2FC433EF for ; Tue, 7 Sep 2021 18:35:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E199061108 for ; Tue, 7 Sep 2021 18:35:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345967AbhIGSgN (ORCPT ); Tue, 7 Sep 2021 14:36:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:52117 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230354AbhIGSgM (ORCPT ); Tue, 7 Sep 2021 14:36:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631039705; 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=39gFd33ByEeHabxlUVexH9bqw8RdJNvKyWEswyYIiZE=; b=TGVhe5PPVYyWX2zdy9Ht/qy+kyjMHAtpDd0BVqLoEWbw0RejQ7j4UT+5ZAXFc102glC3WP MLotvY+RYQBTESc+EfkXl3KGWql6DZkhYqPGR42DeW1Q1BvrG3vemkamhcJ5PclY+tkF22 0YnusWlrseynrzew1TBUfr8y40D8CIc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-323-myDqf5mQPpy7Ly5xvOfCjg-1; Tue, 07 Sep 2021 14:35:02 -0400 X-MC-Unique: myDqf5mQPpy7Ly5xvOfCjg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1AD9F107ACCD; Tue, 7 Sep 2021 18:35:00 +0000 (UTC) Received: from localhost (unknown [10.22.8.230]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5BA836A255; Tue, 7 Sep 2021 18:34:58 +0000 (UTC) Date: Tue, 7 Sep 2021 14:34:57 -0400 From: Eduardo Habkost To: Juergen Gross Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" Subject: Re: [PATCH v2 3/6] x86/kvm: introduce per cpu vcpu masks Message-ID: <20210907183457.53ws6tqqqpzkeil4@habkost.net> References: <20210903130808.30142-1-jgross@suse.com> <20210903130808.30142-4-jgross@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210903130808.30142-4-jgross@suse.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 03, 2021 at 03:08:04PM +0200, Juergen Gross wrote: > In order to support high vcpu numbers per guest don't use on stack > vcpu bitmasks. As all those currently used bitmasks are not used in > functions subject to recursion it is fairly easy to replace them with > percpu bitmasks. > > Disable preemption while such a bitmask is being used in order to > avoid double usage in case we'd switch cpus. > > Signed-off-by: Juergen Gross > --- > V2: > - use local_lock() instead of preempt_disable() (Paolo Bonzini) > --- > arch/x86/include/asm/kvm_host.h | 10 ++++++++++ > arch/x86/kvm/hyperv.c | 25 ++++++++++++++++++------- > arch/x86/kvm/irq_comm.c | 9 +++++++-- > arch/x86/kvm/x86.c | 22 +++++++++++++++++++++- > 4 files changed, 56 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 3513edee8e22..a809a9e4fa5c 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -15,6 +15,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -1591,6 +1592,15 @@ extern bool kvm_has_bus_lock_exit; > /* maximum vcpu-id */ > unsigned int kvm_max_vcpu_id(void); > > +/* per cpu vcpu bitmasks, protected by kvm_pcpu_mask_lock */ > +DECLARE_PER_CPU(local_lock_t, kvm_pcpu_mask_lock); > +extern unsigned long __percpu *kvm_pcpu_vcpu_mask; > +#define KVM_VCPU_MASK_SZ \ > + (sizeof(*kvm_pcpu_vcpu_mask) * BITS_TO_LONGS(KVM_MAX_VCPUS)) > +extern u64 __percpu *kvm_hv_vp_bitmap; > +#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64) > +#define KVM_HV_VPMAP_SZ (sizeof(u64) * KVM_HV_MAX_SPARSE_VCPU_SET_BITS) I have just realized that the Hyper-V sparse bitmap format can support only up to 4096 CPUs, and the current implementation of sparse_set_to_vcpu_mask() won't even work correctly if KVM_MAX_VCPUS is larger than 4096. This means vp_bitmap can't and will never be larger than 512 bytes. Isn't a per-CPU variable for vp_bitmap overkill in this case? > [...] -- Eduardo