From patchwork Thu Apr 1 15:03:04 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicholas Piggin X-Patchwork-Id: 1461226 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=kvm-ppc-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20161025 header.b=o5x803va; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4FB9Zl0jZCz9sXH for ; Fri, 2 Apr 2021 04:45:51 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234506AbhDARoH (ORCPT ); Thu, 1 Apr 2021 13:44:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234620AbhDARi1 (ORCPT ); Thu, 1 Apr 2021 13:38:27 -0400 Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CA82C0F26F3 for ; Thu, 1 Apr 2021 08:05:01 -0700 (PDT) Received: by mail-pf1-x42b.google.com with SMTP id l123so158775pfl.8 for ; Thu, 01 Apr 2021 08:05:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=q5kLhVg/MvykyPPNmMCuNWVc2bIiaBHBOMGefD2pi70=; b=o5x803vaLuhSLiL2m55/F18h/axKjowbv/0eLFEK1BEfhPNw/VYH96aFwytbqBXw7/ 8vzQA0Kl6Y590eyI/6zLOIh4XiS9OOD5GZCsDNHOukGmY+I/3oitK+TNJ2wJc5TRHeKM EIq7tBMspWCpDxapOj8396C0/rcunlNAchb/Y0NL5FA1VeBAAREWxL6NC5nRBNZaK3Bo eGFm3SP1PS/MSqWjSC3rgwsLQ6E4l7VYcQ6FjFRTd2h5gf3CmLMdwcQmKnupJISdL5ze LvrnzfHNm8JzTy7yTtKYK1YM60fZQ3RDj17MJTtbajWQXg4pq8T9Idp6PLGF3sRZr6aA acrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=q5kLhVg/MvykyPPNmMCuNWVc2bIiaBHBOMGefD2pi70=; b=KwmoiYm7b/ffjFzpaawJ+4I7Q+BzTCX34txKE6aODZSupYcmvyVi94RDlkl/13/HFl MFoipz1YlphjttKQZd9hnctzLGGwzCghxFz/dFt3xJrSzJNwlKl5ffelh95PmgMihGAM /mEyDhcXyCjxZz/ymWxbY/9+jjS8plZxxiGX3YINqvGCelRYjoaRhnhtDZsjGfKdzQY0 BXX996yXMMlLw9wDLoKSlHTKU18Q96GEJCNmcn6vHLl19VqejGpbBt/xQl9IdmK+Tewb 4tLIpK6s0bbM5JAjSMc5u2FPQBB4XJDLhxh0WuZ3LyFxrtUGRLp9RAUaLpqnqM+FyxnK sIaQ== X-Gm-Message-State: AOAM533XHoCujGGv/l/5N+mk7eZgvrWsuw1nINYAf+AKb3lhdoRZW5BF i2NT1ejYdpDKmLGA5+rtJ12D86bHpP4= X-Google-Smtp-Source: ABdhPJx8LV+GqfZ+ydBxBTgRLBsgiGqZmiv4U0JPdlfOj8dd8zWmoiGU/1i3txf4PH8zazf/csVeGw== X-Received: by 2002:a63:a54:: with SMTP id z20mr7879950pgk.228.1617289500976; Thu, 01 Apr 2021 08:05:00 -0700 (PDT) Received: from bobo.ibm.com ([1.128.218.207]) by smtp.gmail.com with ESMTPSA id l3sm5599632pju.44.2021.04.01.08.04.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Apr 2021 08:05:00 -0700 (PDT) From: Nicholas Piggin To: kvm-ppc@vger.kernel.org Cc: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org Subject: [PATCH v5 27/48] KVM: PPC: Book3S HV P9: Reduce irq_work vs guest decrementer races Date: Fri, 2 Apr 2021 01:03:04 +1000 Message-Id: <20210401150325.442125-28-npiggin@gmail.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20210401150325.442125-1-npiggin@gmail.com> References: <20210401150325.442125-1-npiggin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm-ppc@vger.kernel.org irq_work's use of the DEC SPR is racy with guest<->host switch and guest entry which flips the DEC interrupt to guest, which could lose a host work interrupt. This patch closes one race, and attempts to comment another class of races. Signed-off-by: Nicholas Piggin --- arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 46f457c3b828..6cfac8f553f6 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3755,6 +3755,18 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, if (!(vcpu->arch.ctrl & 1)) mtspr(SPRN_CTRLT, mfspr(SPRN_CTRLF) & ~1); + /* + * When setting DEC, we must always deal with irq_work_raise via NMI vs + * setting DEC. The problem occurs right as we switch into guest mode + * if a NMI hits and sets pending work and sets DEC, then that will + * apply to the guest and not bring us back to the host. + * + * irq_work_raise could check a flag (or possibly LPCR[HDICE] for + * example) and set HDEC to 1? That wouldn't solve the nested hv + * case which needs to abort the hcall or zero the time limit. + * + * XXX: Another day's problem. + */ mtspr(SPRN_DEC, vcpu->arch.dec_expires - tb); if (kvmhv_on_pseries()) { @@ -3891,6 +3903,9 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, next_timer = timer_get_next_tb(); mtspr(SPRN_DEC, next_timer - tb); + /* We may have raced with new irq work */ + if (test_irq_work_pending()) + set_dec(1); mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso); kvmhv_load_host_pmu();