From patchwork Mon Nov 2 09:46:28 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Juergen Gross X-Patchwork-Id: 317322 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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham 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 770F0C4742C for ; Mon, 2 Nov 2020 09:46:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C091223B0 for ; Mon, 2 Nov 2020 09:46:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="oprJF7WU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728266AbgKBJqk (ORCPT ); Mon, 2 Nov 2020 04:46:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:59242 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728183AbgKBJqk (ORCPT ); Mon, 2 Nov 2020 04:46:40 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1604310398; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=17FMAHhs4YL1/t0+anTrzXuWljmDTLAYkMFKjnFnPu8=; b=oprJF7WUJrIvUMKP0D4ps5E/S1v1WiilVNN6CG+fSekXIPeuKaaMHtQBxb87LMkp0A++mX JzB63cj6CS2eSbTDqIu9I4HEkG9/dRrQRVk/186k+IBEs5H6v3uPEsafNbC/fpX/hNCWMu E8XeYM3h0LmQh/WkjZjI5p4r9/Jt9eI= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B3CB2AEAB for ; Mon, 2 Nov 2020 09:46:38 +0000 (UTC) From: Juergen Gross To: stable@vger.kernel.org Subject: [PATCH 03/13] xen/events: fix race in evtchn_fifo_unmask() Date: Mon, 2 Nov 2020 10:46:28 +0100 Message-Id: <20201102094638.3355-4-jgross@suse.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201102094638.3355-1-jgross@suse.com> References: <20201102094638.3355-1-jgross@suse.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Unmasking a fifo event channel can result in unmasking it twice, once directly in the kernel and once via a hypercall in case the event was pending. Fix that by doing the local unmask only if the event is not pending. This is part of XSA-332. This is upstream commit f01337197419b7e8a492e83089552b77d3b5fb90 Cc: stable@vger.kernel.org Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- drivers/xen/events/events_fifo.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c index 76b318e88382..3071256a9413 100644 --- a/drivers/xen/events/events_fifo.c +++ b/drivers/xen/events/events_fifo.c @@ -227,19 +227,25 @@ static bool evtchn_fifo_is_masked(unsigned port) return sync_test_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word)); } /* - * Clear MASKED, spinning if BUSY is set. + * Clear MASKED if not PENDING, spinning if BUSY is set. + * Return true if mask was cleared. */ -static void clear_masked(volatile event_word_t *word) +static bool clear_masked_cond(volatile event_word_t *word) { event_word_t new, old, w; w = *word; do { + if (w & (1 << EVTCHN_FIFO_PENDING)) + return false; + old = w & ~(1 << EVTCHN_FIFO_BUSY); new = old & ~(1 << EVTCHN_FIFO_MASKED); w = sync_cmpxchg(word, old, new); } while (w != old); + + return true; } static void evtchn_fifo_unmask(unsigned port) @@ -248,8 +254,7 @@ static void evtchn_fifo_unmask(unsigned port) BUG_ON(!irqs_disabled()); - clear_masked(word); - if (evtchn_fifo_is_pending(port)) { + if (!clear_masked_cond(word)) { struct evtchn_unmask unmask = { .port = port }; (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask); }