From patchwork Sat Oct 9 02:11:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 12546861 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 0843BC433F5 for ; Sat, 9 Oct 2021 02:12:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9D3360F5E for ; Sat, 9 Oct 2021 02:12:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244187AbhJICOr (ORCPT ); Fri, 8 Oct 2021 22:14:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38186 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244180AbhJICOq (ORCPT ); Fri, 8 Oct 2021 22:14:46 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DDE9CC061765 for ; Fri, 8 Oct 2021 19:12:49 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id t7-20020a258387000000b005b6d7220c79so14963945ybk.16 for ; Fri, 08 Oct 2021 19:12:49 -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=VOf0o+drOoyjtnZHAjwPMyY2QgjmuejeI8ZGvk5qQh8=; b=c594JBXBzlzJm/B4MJiuak37F10cOGqzZRDRYYkHvGtg+tYhi9bkpT7HAvzA4a7CrO wY9eJk+8SXC6VXSYxm/HtIH7HCqw4WmraTlKbDvDXkb0ieGHnQEdhLp9SHTOoF1D+ihb l0NC5UfvB9mBvn0GShFPrhMJGBfjxpiBY5BrX5s0xEdDxmIpWuxZBBx29TlMmh0JGg0R lof8oMgaYbwVizPYN+9qQPXHfvL56RO9ccLyp7IYNiT8OQ7d02343dCZy83nOSQGhHOM xfDcm3J7v9Zaqb3Cv7KhQ0mVfu7vqET/6w/svCdKYDLPxqzAsRNGhLifWQMr9xoyFcPL LUIA== 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=VOf0o+drOoyjtnZHAjwPMyY2QgjmuejeI8ZGvk5qQh8=; b=NFhQCApQWM+wsAPM9rCUEqZ4Ygp2OUrUf8eguf1AJcUsvN0KcA7mm50ErB81Dp5qBT vuRdf5NUSBOSQyEFA2piHuyy1vxY57eeisxHIK4ALVM63Mpdi62fP63TxwnZTa4GcUmf MBQ/isl5rXF8cPshbzQBGLYazz+m3pk7EjnTwznI5VSnOq6q3fKKIQE2x2AIoek8OkDN /gJ6YD5tv1hcFVBuChRbME42D1noUIG1649s3oQ4jq2W1RwIxi1b4UBtkhRHp59DQwbZ Yu9QxI8I3wjkeiOmjqYYe3LQJRM/DyNMZhbsIe/i889eGSp6HNVRGEpMHhcfoGNw3nki J7VQ== X-Gm-Message-State: AOAM531yaOZ4dsUbfcrpktkKcMNa20JsZ01Y7ZCEh0viN3CbRFMwk6eV XhAIxSlFlRZu6DsJzyZ/PsBCesGrgn8= X-Google-Smtp-Source: ABdhPJzvUj+lYxE1uvv63+XvvDPeheCH+oyqg89jaLQyiP8PVpc/MK53zetbWHLCR1OXSf8DRfROgUDiyR0= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:90:200:e39b:6333:b001:cb]) (user=seanjc job=sendgmr) by 2002:a25:d915:: with SMTP id q21mr7203996ybg.17.1633745569082; Fri, 08 Oct 2021 19:12:49 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 8 Oct 2021 19:11:56 -0700 In-Reply-To: <20211009021236.4122790-1-seanjc@google.com> Message-Id: <20211009021236.4122790-4-seanjc@google.com> Mime-Version: 1.0 References: <20211009021236.4122790-1-seanjc@google.com> X-Mailer: git-send-email 2.33.0.882.g93a45727a2-goog Subject: [PATCH v2 03/43] 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 , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini Cc: James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , 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, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang Precedence: bulk List-ID: X-Mailing-List: linux-mips@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") Reviewed-by: 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 3f6d450355f0..7bc38549487e 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) {