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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F9B9C433EF for ; Sat, 25 Sep 2021 00:55:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 284CF61260 for ; Sat, 25 Sep 2021 00:55:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345918AbhIYA5L (ORCPT ); Fri, 24 Sep 2021 20:57:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345964AbhIYA5H (ORCPT ); Fri, 24 Sep 2021 20:57:07 -0400 Received: from mail-qk1-x74a.google.com (mail-qk1-x74a.google.com [IPv6:2607:f8b0:4864:20::74a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1527C061613 for ; Fri, 24 Sep 2021 17:55:33 -0700 (PDT) Received: by mail-qk1-x74a.google.com with SMTP id p23-20020a05620a22f700b003d5ac11ac5cso44221303qki.15 for ; Fri, 24 Sep 2021 17:55:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=s8Ef8GFuvQfnF9BDar9o1LMsjHo/kVSjkp6RQOizXjk=; b=G61LH4mFxuFNSPc8dYANo1eT4LoYTtllF8CmUigAVUwE47niN3IxCLvz7gdu3kXJ4p ZQGRUPxd6lVd1pie3osAQPOxmbLJto1U72TFRKzU7SrEeLnRgNzwFM67EhN9OMHtfLK4 0P8CpLo4DBhmRIO3KNivDhM66x7e790LPKbt1kMUUoaEFJ8BrQ0kHU4SkwA9CnUG4ZvG NOgccEjti04droRcKSejfuWWOI2KRU0PMG/o1TrFggkFEC3/F7K7dtkErqqSnuV7wQju UsaZQRj+Ze+2OUu3FUTytK0ap4L7DtgKMjJqvpn6WamsAAvTkNWZ6Fzz7ReqK7CQj28q kOig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=s8Ef8GFuvQfnF9BDar9o1LMsjHo/kVSjkp6RQOizXjk=; b=Cyp4TSWy3l5mn1tAXdJkXsXQGFrSg6ccaZdup4t1Ib4veRkB1CYzNZ72GZQMk4aPEn uJp0tjtQoB6unKsgJpmSo8WsXFt6dyDNgX/Cn7FCWs32R+M5uVGyPWaWJa5KGA/Ffgsw o8KK92pDNEH2eeOxOS0Z2B2CIkfuyGn3m2UE284t7TMVuDUbii+m17lGzObluLanh4Qq FMIYzT26m8waAR1OOCapD8AMXjeh4xn3k7eqpw35JBnys2JcMp6HWnU4/t8rw82ApMyH U7wD4wMlEPmrZliMewCxVbOO2YA2A4TUGlpkgSObBGJsfe7D5YhUX0eBMRIGLBWrC1E5 /STw== X-Gm-Message-State: AOAM5315LSCTp0JXVEoV4kMLXJBNH7aLijP+RFmYNQDtQmBujNZn7cM/ FXmQ8QHlDPaKk2YE+rpoNCiSzfDeCxw= X-Google-Smtp-Source: ABdhPJz4KlXw4aFKDakmak5VHFe0t/03Im2jas/e5lfzq06w+q+oBXLEOxDY5zwYzZ40nGkko5J4YoUheek= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:90:200:4c72:89be:dba3:2bcb]) (user=seanjc job=sendgmr) by 2002:a05:6214:2d1:: with SMTP id g17mr13106407qvu.63.1632531332975; Fri, 24 Sep 2021 17:55:32 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 24 Sep 2021 17:55:15 -0700 In-Reply-To: <20210925005528.1145584-1-seanjc@google.com> Message-Id: <20210925005528.1145584-2-seanjc@google.com> Mime-Version: 1.0 References: <20210925005528.1145584-1-seanjc@google.com> X-Mailer: git-send-email 2.33.0.685.g46640cef36-goog Subject: [PATCH 01/14] KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU From: Sean Christopherson To: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , Paolo Bonzini Cc: James Morse , Alexandru Elisei , Suzuki K Poulose , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, David Matlack , Jing Zhang Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Wrap s390's halt_poll_max_steal with READ_ONCE and snapshot the result of kvm_arch_no_poll() in kvm_vcpu_block() to avoid a mostly-theoretical, largely benign bug on s390 where the result of kvm_arch_no_poll() could change due to userspace modifying halt_poll_max_steal while the vCPU is blocking. The bug is largely benign as it will either cause KVM to skip updating halt-polling times (no_poll toggles false=>true) or to update halt-polling times with a slightly flawed block_ns. Note, READ_ONCE is unnecessary in the current code, add it in case the arch hook is ever inlined, and to provide a hint that userspace can change the param at will. Fixes: 8b905d28ee17 ("KVM: s390: provide kvm_arch_no_poll function") Cc: Christian Borntraeger Signed-off-by: Sean Christopherson --- arch/s390/kvm/kvm-s390.c | 2 +- virt/kvm/kvm_main.c | 5 +++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 6a6dd5e1daf6..7cabe6778b1b 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3446,7 +3446,7 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) { /* do not poll with more than halt_poll_max_steal percent of steal time */ if (S390_lowcore.avg_steal_timer * 100 / (TICK_USEC << 12) >= - halt_poll_max_steal) { + READ_ONCE(halt_poll_max_steal)) { vcpu->stat.halt_no_poll_steal++; return true; } diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 191dac6b1bed..768a4cbb26a6 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3213,6 +3213,7 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited) */ void kvm_vcpu_block(struct kvm_vcpu *vcpu) { + bool halt_poll_allowed = !kvm_arch_no_poll(vcpu); ktime_t start, cur, poll_end; bool waited = false; u64 block_ns; @@ -3220,7 +3221,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) kvm_arch_vcpu_blocking(vcpu); start = cur = poll_end = ktime_get(); - if (vcpu->halt_poll_ns && !kvm_arch_no_poll(vcpu)) { + if (vcpu->halt_poll_ns && halt_poll_allowed) { ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); ++vcpu->stat.generic.halt_attempted_poll; @@ -3275,7 +3276,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) update_halt_poll_stats( vcpu, ktime_to_ns(ktime_sub(poll_end, start)), waited); - if (!kvm_arch_no_poll(vcpu)) { + if (halt_poll_allowed) { if (!vcpu_valid_wakeup(vcpu)) { shrink_halt_poll_ns(vcpu); } else if (vcpu->kvm->max_halt_poll_ns) { -- 2.33.0.685.g46640cef36-goog