From patchwork Thu Nov 13 17:42:09 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Roger_Pau_Monn=C3=A9?= X-Patchwork-Id: 410529 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 4F2A11400AB for ; Fri, 14 Nov 2014 05:01:59 +1100 (AEDT) Received: from localhost ([::1]:33251 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XoyiT-0006ks-AX for incoming@patchwork.ozlabs.org; Thu, 13 Nov 2014 13:01:57 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50605) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xoyi9-0006TC-15 for qemu-devel@nongnu.org; Thu, 13 Nov 2014 13:01:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xoyi4-0000QP-Oq for qemu-devel@nongnu.org; Thu, 13 Nov 2014 13:01:36 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:17702) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xoyi4-0000QG-G7 for qemu-devel@nongnu.org; Thu, 13 Nov 2014 13:01:32 -0500 X-IronPort-AV: E=Sophos;i="5.07,379,1413244800"; d="scan'208";a="192510401" From: Roger Pau Monne To: , Date: Thu, 13 Nov 2014 18:42:09 +0100 Message-ID: <1415900529-10629-1-git-send-email-roger.pau@citrix.com> X-Mailer: git-send-email 1.9.3 (Apple Git-50) MIME-Version: 1.0 X-DLP: MIA2 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 66.165.176.63 Cc: Kevin Wolf , Konrad Rzeszutek Wilk , George Dunlap , Stefano Stabellini , Stefan Hajnoczi , Roger Pau Monne Subject: [Qemu-devel] [PATCH v3 for-xen-4.5] xen_disk: fix unmapping of persistent grants X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org This patch fixes two issues with persistent grants and the disk PV backend (Qdisk): - Keep track of memory regions where persistent grants have been mapped since we need to unmap them as a whole. It is not possible to unmap a single grant if it has been batch-mapped. A new check has also been added to make sure persistent grants are only used if the whole mapped region can be persistently mapped in the batch_maps case. - Unmap persistent grants before switching to the closed state, so the frontend can also free them. Signed-off-by: Roger Pau Monné Reported-by: George Dunlap Cc: Stefano Stabellini Cc: Kevin Wolf Cc: Stefan Hajnoczi Cc: George Dunlap Cc: Konrad Rzeszutek Wilk Tested-by: George Dunlap Acked-by: Stefano Stabellini --- Xen release exception: this is obviously an important bug-fix that should be included in 4.5. Without this fix, trying to do a block-detach of a Qdisk from a running guest can lead to guest crash depending on the blkfront implementation. --- Changea since v2: - Expand the commit message to mention the newly added check. - Don't use persistent_regions in the !batch_maps case, we can use the previous implementation which works fine in that case. Changes since v1: - Instead of disabling batch mappings when using persistent grants, keep track of the persistently mapped regions and unmap them on disconnection. This prevents unmapping single persistent grants, but the current implementation doesn't require it. This new version is slightly faster than the previous one, the following test results are in IOPS from 20 runs of a block-attach, fio run, block-detach test loop: x batch + no_batch +----------------------------------------------------------------------+ | + + x x + + + x xx x | |+ + x x+ *+++ * +x* +++x* x xx x *| | |_____________A_____M______|| | |________________A_____M___________| | +----------------------------------------------------------------------+ N Min Max Median Avg Stddev x 20 52941 63822 62396 61180.15 2673.6497 + 20 49967 63849 60322 59116.9 3456.3455 Difference at 95.0% confidence -2063.25 +/- 1977.66 -3.37242% +/- 3.23252% (Student's t, pooled s = 3089.88) --- hw/block/xen_disk.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 66 insertions(+), 6 deletions(-) diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c index 231e9a7..21842a0 100644 --- a/hw/block/xen_disk.c +++ b/hw/block/xen_disk.c @@ -59,6 +59,13 @@ struct PersistentGrant { typedef struct PersistentGrant PersistentGrant; +struct PersistentRegion { + void *addr; + int num; +}; + +typedef struct PersistentRegion PersistentRegion; + struct ioreq { blkif_request_t req; int16_t status; @@ -118,6 +125,7 @@ struct XenBlkDev { gboolean feature_discard; gboolean feature_persistent; GTree *persistent_gnts; + GSList *persistent_regions; unsigned int persistent_gnt_count; unsigned int max_grants; @@ -177,6 +185,23 @@ static void destroy_grant(gpointer pgnt) g_free(grant); } +static void remove_persistent_region(gpointer data, gpointer dev) +{ + PersistentRegion *region = data; + struct XenBlkDev *blkdev = dev; + XenGnttab gnt = blkdev->xendev.gnttabdev; + + if (xc_gnttab_munmap(gnt, region->addr, region->num) != 0) { + xen_be_printf(&blkdev->xendev, 0, + "xc_gnttab_munmap region %p failed: %s\n", + region->addr, strerror(errno)); + } + xen_be_printf(&blkdev->xendev, 3, + "unmapped grant region %p with %d pages\n", + region->addr, region->num); + g_free(region); +} + static struct ioreq *ioreq_start(struct XenBlkDev *blkdev) { struct ioreq *ioreq = NULL; @@ -343,6 +368,7 @@ static int ioreq_map(struct ioreq *ioreq) void *page[BLKIF_MAX_SEGMENTS_PER_REQUEST]; int i, j, new_maps = 0; PersistentGrant *grant; + PersistentRegion *region; /* domids and refs variables will contain the information necessary * to map the grants that are needed to fulfill this request. * @@ -421,7 +447,22 @@ static int ioreq_map(struct ioreq *ioreq) } } } - if (ioreq->blkdev->feature_persistent) { + if (ioreq->blkdev->feature_persistent && new_maps != 0 && + (!batch_maps || (ioreq->blkdev->persistent_gnt_count + new_maps <= + ioreq->blkdev->max_grants))) { + /* + * If we are using persistent grants and batch mappings only + * add the new maps to the list of persistent grants if the whole + * area can be persistently mapped. + */ + if (batch_maps) { + region = g_malloc0(sizeof(*region)); + region->addr = ioreq->pages; + region->num = new_maps; + ioreq->blkdev->persistent_regions = g_slist_append( + ioreq->blkdev->persistent_regions, + region); + } while ((ioreq->blkdev->persistent_gnt_count < ioreq->blkdev->max_grants) && new_maps) { /* Go through the list of newly mapped grants and add as many @@ -447,6 +488,7 @@ static int ioreq_map(struct ioreq *ioreq) grant); ioreq->blkdev->persistent_gnt_count++; } + assert(!batch_maps || new_maps == 0); } for (i = 0; i < ioreq->v.niov; i++) { ioreq->v.iov[i].iov_base += (uintptr_t)page[i]; @@ -971,7 +1013,10 @@ static int blk_connect(struct XenDevice *xendev) blkdev->max_grants = max_requests * BLKIF_MAX_SEGMENTS_PER_REQUEST; blkdev->persistent_gnts = g_tree_new_full((GCompareDataFunc)int_cmp, NULL, NULL, + batch_maps ? + (GDestroyNotify)g_free : (GDestroyNotify)destroy_grant); + blkdev->persistent_regions = NULL; blkdev->persistent_gnt_count = 0; } @@ -1000,6 +1045,26 @@ static void blk_disconnect(struct XenDevice *xendev) blkdev->cnt_map--; blkdev->sring = NULL; } + + /* + * Unmap persistent grants before switching to the closed state + * so the frontend can free them. + * + * In the !batch_maps case g_tree_destroy will take care of unmapping + * the grant, but in the batch_maps case we need to iterate over every + * region in persistent_regions and unmap it. + */ + if (blkdev->feature_persistent) { + g_tree_destroy(blkdev->persistent_gnts); + assert(batch_maps || blkdev->persistent_gnt_count == 0); + if (batch_maps) { + blkdev->persistent_gnt_count = 0; + g_slist_foreach(blkdev->persistent_regions, + (GFunc)remove_persistent_region, blkdev); + g_slist_free(blkdev->persistent_regions); + } + blkdev->feature_persistent = false; + } } static int blk_free(struct XenDevice *xendev) @@ -1011,11 +1076,6 @@ static int blk_free(struct XenDevice *xendev) blk_disconnect(xendev); } - /* Free persistent grants */ - if (blkdev->feature_persistent) { - g_tree_destroy(blkdev->persistent_gnts); - } - while (!QLIST_EMPTY(&blkdev->freelist)) { ioreq = QLIST_FIRST(&blkdev->freelist); QLIST_REMOVE(ioreq, list);