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 87BF8C43217 for ; Tue, 25 Jan 2022 00:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2373898AbiAYAPb (ORCPT ); Mon, 24 Jan 2022 19:15:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1458146AbiAXX2Q (ORCPT ); Mon, 24 Jan 2022 18:28:16 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EE822C01D7FE; Mon, 24 Jan 2022 13:32:35 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B6232B80CCF; Mon, 24 Jan 2022 21:32:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC25BC340E5; Mon, 24 Jan 2022 21:32:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643059953; bh=hwKZ0mbwkBWAvdVxC0dHLJH2tEpOKFeWFTrJfS+VJ18=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bPWNwwZ0/uE5b+0xdVTyO2QdZv3DKsO1LEThuoSe9pU7tNXTL7H1ZmGYu9BHtLq8c 3WdjXsoDcAOg65je6DGRiEuhwC2d+zmwPfrS6QSBhsQhY2ARjDLcEZFrT3XbVsCLdL sAsHFi0hFDxaTV7XW43/PP//HdC6Oo+D71YLTV+s= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christian Borntraeger , Sean Christopherson , Paolo Bonzini , Sasha Levin Subject: [PATCH 5.16 0789/1039] KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU Date: Mon, 24 Jan 2022 19:42:58 +0100 Message-Id: <20220124184151.815314575@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124184125.121143506@linuxfoundation.org> References: <20220124184125.121143506@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sean Christopherson [ Upstream commit 6f390916c4fb359507d9ac4bf1b28a4f8abee5c0 ] 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 Message-Id: <20211009021236.4122790-4-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- 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 ef299aad40090..8fc9c79c899b5 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3449,7 +3449,7 @@ 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 72c4e6b393896..5bd62342c482b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3153,6 +3153,7 @@ 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; @@ -3160,7 +3161,7 @@ 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; @@ -3215,7 +3216,7 @@ out: 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) { -- 2.34.1