[Qemu-devel] [PULL 12/15] xen_disk: remove use of grant map/unmap

[Stefano Stabellini <sstabellini@kernel.org>]

From: Paul Durrant <paul.durrant@citrix.com>

Now that the (native or emulated) xen_be_copy_grant_refs() helper is
always available, the xen_disk code can be significantly simplified by
removing direct use of grant map and unmap operations.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
---
 hw/block/xen_disk.c | 352 ++++------------------------------------------------
 1 file changed, 25 insertions(+), 327 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index d3be45a..28be8b6 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -36,27 +36,9 @@
 
 /* ------------------------------------------------------------- */
 
-static int batch_maps   = 0;
-
-/* ------------------------------------------------------------- */
-
 #define BLOCK_SIZE  512
 #define IOCB_COUNT  (BLKIF_MAX_SEGMENTS_PER_REQUEST + 2)
 
-struct PersistentGrant {
-    void *page;
-    struct XenBlkDev *blkdev;
-};
-
-typedef struct PersistentGrant PersistentGrant;
-
-struct PersistentRegion {
-    void *addr;
-    int num;
-};
-
-typedef struct PersistentRegion PersistentRegion;
-
 struct ioreq {
     blkif_request_t     req;
     int16_t             status;
@@ -65,14 +47,11 @@ struct ioreq {
     off_t               start;
     QEMUIOVector        v;
     int                 presync;
-    uint8_t             mapped;
 
     /* grant mapping */
     uint32_t            refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-    int                 prot;
     void                *page[BLKIF_MAX_SEGMENTS_PER_REQUEST];
     void                *pages;
-    int                 num_unmap;
 
     /* aio status */
     int                 aio_inflight;
@@ -103,7 +82,6 @@ struct XenBlkDev {
     int                 protocol;
     blkif_back_rings_t  rings;
     int                 more_work;
-    int                 cnt_map;
 
     /* request lists */
     QLIST_HEAD(inflight_head, ioreq) inflight;
@@ -114,13 +92,7 @@ struct XenBlkDev {
     int                 requests_finished;
     unsigned int        max_requests;
 
-    /* Persistent grants extension */
     gboolean            feature_discard;
-    gboolean            feature_persistent;
-    GTree               *persistent_gnts;
-    GSList              *persistent_regions;
-    unsigned int        persistent_gnt_count;
-    unsigned int        max_grants;
 
     /* qemu block driver */
     DriveInfo           *dinfo;
@@ -139,10 +111,8 @@ static void ioreq_reset(struct ioreq *ioreq)
     ioreq->status = 0;
     ioreq->start = 0;
     ioreq->presync = 0;
-    ioreq->mapped = 0;
 
     memset(ioreq->refs, 0, sizeof(ioreq->refs));
-    ioreq->prot = 0;
     memset(ioreq->page, 0, sizeof(ioreq->page));
     ioreq->pages = NULL;
 
@@ -156,37 +126,6 @@ static void ioreq_reset(struct ioreq *ioreq)
     qemu_iovec_reset(&ioreq->v);
 }
 
-static gint int_cmp(gconstpointer a, gconstpointer b, gpointer user_data)
-{
-    uint ua = GPOINTER_TO_UINT(a);
-    uint ub = GPOINTER_TO_UINT(b);
-    return (ua > ub) - (ua < ub);
-}
-
-static void destroy_grant(gpointer pgnt)
-{
-    PersistentGrant *grant = pgnt;
-    struct XenBlkDev *blkdev = grant->blkdev;
-    struct XenDevice *xendev = &blkdev->xendev;
-
-    xen_be_unmap_grant_ref(xendev, grant->page);
-    grant->blkdev->persistent_gnt_count--;
-    xen_pv_printf(xendev, 3, "unmapped grant %p\n", grant->page);
-    g_free(grant);
-}
-
-static void remove_persistent_region(gpointer data, gpointer dev)
-{
-    PersistentRegion *region = data;
-    struct XenBlkDev *blkdev = dev;
-    struct XenDevice *xendev = &blkdev->xendev;
-
-    xen_be_unmap_grant_refs(xendev, region->addr, region->num);
-    xen_pv_printf(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;
@@ -254,7 +193,6 @@ static int ioreq_parse(struct ioreq *ioreq)
                   ioreq->req.handle, ioreq->req.id, ioreq->req.sector_number);
     switch (ioreq->req.operation) {
     case BLKIF_OP_READ:
-        ioreq->prot = PROT_WRITE; /* to memory */
         break;
     case BLKIF_OP_FLUSH_DISKCACHE:
         ioreq->presync = 1;
@@ -263,7 +201,6 @@ static int ioreq_parse(struct ioreq *ioreq)
         }
         /* fall through */
     case BLKIF_OP_WRITE:
-        ioreq->prot = PROT_READ; /* from memory */
         break;
     case BLKIF_OP_DISCARD:
         return 0;
@@ -310,171 +247,6 @@ err:
     return -1;
 }
 
-static void ioreq_unmap(struct ioreq *ioreq)
-{
-    struct XenBlkDev *blkdev = ioreq->blkdev;
-    struct XenDevice *xendev = &blkdev->xendev;
-    int i;
-
-    if (ioreq->num_unmap == 0 || ioreq->mapped == 0) {
-        return;
-    }
-    if (batch_maps) {
-        if (!ioreq->pages) {
-            return;
-        }
-        xen_be_unmap_grant_refs(xendev, ioreq->pages, ioreq->num_unmap);
-        ioreq->blkdev->cnt_map -= ioreq->num_unmap;
-        ioreq->pages = NULL;
-    } else {
-        for (i = 0; i < ioreq->num_unmap; i++) {
-            if (!ioreq->page[i]) {
-                continue;
-            }
-            xen_be_unmap_grant_ref(xendev, ioreq->page[i]);
-            ioreq->blkdev->cnt_map--;
-            ioreq->page[i] = NULL;
-        }
-    }
-    ioreq->mapped = 0;
-}
-
-static int ioreq_map(struct ioreq *ioreq)
-{
-    struct XenBlkDev *blkdev = ioreq->blkdev;
-    struct XenDevice *xendev = &blkdev->xendev;
-    uint32_t refs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-    void *page[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-    int i, j, new_maps = 0;
-    PersistentGrant *grant;
-    PersistentRegion *region;
-    /* refs variable will contain the information necessary
-     * to map the grants that are needed to fulfill this request.
-     *
-     * After mapping the needed grants, the page array will contain the
-     * memory address of each granted page in the order specified in ioreq
-     * (disregarding if it's a persistent grant or not).
-     */
-
-    if (ioreq->v.niov == 0 || ioreq->mapped == 1) {
-        return 0;
-    }
-    if (ioreq->blkdev->feature_persistent) {
-        for (i = 0; i < ioreq->v.niov; i++) {
-            grant = g_tree_lookup(ioreq->blkdev->persistent_gnts,
-                                    GUINT_TO_POINTER(ioreq->refs[i]));
-
-            if (grant != NULL) {
-                page[i] = grant->page;
-                xen_pv_printf(&ioreq->blkdev->xendev, 3,
-                              "using persistent-grant %" PRIu32 "\n",
-                              ioreq->refs[i]);
-            } else {
-                    /* Add the grant to the list of grants that
-                     * should be mapped
-                     */
-                    refs[new_maps] = ioreq->refs[i];
-                    page[i] = NULL;
-                    new_maps++;
-            }
-        }
-        /* Set the protection to RW, since grants may be reused later
-         * with a different protection than the one needed for this request
-         */
-        ioreq->prot = PROT_WRITE | PROT_READ;
-    } else {
-        /* All grants in the request should be mapped */
-        memcpy(refs, ioreq->refs, sizeof(refs));
-        memset(page, 0, sizeof(page));
-        new_maps = ioreq->v.niov;
-    }
-
-    if (batch_maps && new_maps) {
-        ioreq->pages = xen_be_map_grant_refs(xendev, refs, new_maps,
-                                             ioreq->prot);
-        if (ioreq->pages == NULL) {
-            xen_pv_printf(&ioreq->blkdev->xendev, 0,
-                          "can't map %d grant refs (%s, %d maps)\n",
-                          new_maps, strerror(errno), ioreq->blkdev->cnt_map);
-            return -1;
-        }
-        for (i = 0, j = 0; i < ioreq->v.niov; i++) {
-            if (page[i] == NULL) {
-                page[i] = ioreq->pages + (j++) * XC_PAGE_SIZE;
-            }
-        }
-        ioreq->blkdev->cnt_map += new_maps;
-    } else if (new_maps)  {
-        for (i = 0; i < new_maps; i++) {
-            ioreq->page[i] = xen_be_map_grant_ref(xendev, refs[i],
-                                                  ioreq->prot);
-            if (ioreq->page[i] == NULL) {
-                xen_pv_printf(&ioreq->blkdev->xendev, 0,
-                              "can't map grant ref %d (%s, %d maps)\n",
-                              refs[i], strerror(errno), ioreq->blkdev->cnt_map);
-                ioreq->mapped = 1;
-                ioreq_unmap(ioreq);
-                return -1;
-            }
-            ioreq->blkdev->cnt_map++;
-        }
-        for (i = 0, j = 0; i < ioreq->v.niov; i++) {
-            if (page[i] == NULL) {
-                page[i] = ioreq->page[j++];
-            }
-        }
-    }
-    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
-             * as possible to the list of persistently mapped grants.
-             *
-             * Since we start at the end of ioreq->page(s), we only need
-             * to decrease new_maps to prevent this granted pages from
-             * being unmapped in ioreq_unmap.
-             */
-            grant = g_malloc0(sizeof(*grant));
-            new_maps--;
-            if (batch_maps) {
-                grant->page = ioreq->pages + (new_maps) * XC_PAGE_SIZE;
-            } else {
-                grant->page = ioreq->page[new_maps];
-            }
-            grant->blkdev = ioreq->blkdev;
-            xen_pv_printf(&ioreq->blkdev->xendev, 3,
-                          "adding grant %" PRIu32 " page: %p\n",
-                          refs[new_maps], grant->page);
-            g_tree_insert(ioreq->blkdev->persistent_gnts,
-                          GUINT_TO_POINTER(refs[new_maps]),
-                          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];
-    }
-    ioreq->mapped = 1;
-    ioreq->num_unmap = new_maps;
-    return 0;
-}
-
 static void ioreq_free_copy_buffers(struct ioreq *ioreq)
 {
     int i;
@@ -570,32 +342,28 @@ static void qemu_aio_complete(void *opaque, int ret)
         goto done;
     }
 
-    if (xen_feature_grant_copy) {
-        switch (ioreq->req.operation) {
-        case BLKIF_OP_READ:
-            /* in case of failure ioreq->aio_errors is increased */
-            if (ret == 0) {
-                ioreq_grant_copy(ioreq);
-            }
-            ioreq_free_copy_buffers(ioreq);
-            break;
-        case BLKIF_OP_WRITE:
-        case BLKIF_OP_FLUSH_DISKCACHE:
-            if (!ioreq->req.nr_segments) {
-                break;
-            }
-            ioreq_free_copy_buffers(ioreq);
-            break;
-        default:
+    switch (ioreq->req.operation) {
+    case BLKIF_OP_READ:
+        /* in case of failure ioreq->aio_errors is increased */
+        if (ret == 0) {
+            ioreq_grant_copy(ioreq);
+        }
+        ioreq_free_copy_buffers(ioreq);
+        break;
+    case BLKIF_OP_WRITE:
+    case BLKIF_OP_FLUSH_DISKCACHE:
+        if (!ioreq->req.nr_segments) {
             break;
         }
+        ioreq_free_copy_buffers(ioreq);
+        break;
+    default:
+        break;
     }
 
     ioreq->status = ioreq->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
-    if (!xen_feature_grant_copy) {
-        ioreq_unmap(ioreq);
-    }
     ioreq_finish(ioreq);
+
     switch (ioreq->req.operation) {
     case BLKIF_OP_WRITE:
     case BLKIF_OP_FLUSH_DISKCACHE:
@@ -655,18 +423,13 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
 {
     struct XenBlkDev *blkdev = ioreq->blkdev;
 
-    if (xen_feature_grant_copy) {
-        ioreq_init_copy_buffers(ioreq);
-        if (ioreq->req.nr_segments && (ioreq->req.operation == BLKIF_OP_WRITE ||
-            ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
-            ioreq_grant_copy(ioreq)) {
-                ioreq_free_copy_buffers(ioreq);
-                goto err;
-        }
-    } else {
-        if (ioreq->req.nr_segments && ioreq_map(ioreq)) {
-            goto err;
-        }
+    ioreq_init_copy_buffers(ioreq);
+    if (ioreq->req.nr_segments &&
+        (ioreq->req.operation == BLKIF_OP_WRITE ||
+         ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
+        ioreq_grant_copy(ioreq)) {
+        ioreq_free_copy_buffers(ioreq);
+        goto err;
     }
 
     ioreq->aio_inflight++;
@@ -707,9 +470,6 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
     }
     default:
         /* unknown operation (shouldn't happen -- parse catches this) */
-        if (!xen_feature_grant_copy) {
-            ioreq_unmap(ioreq);
-        }
         goto err;
     }
 
@@ -895,10 +655,6 @@ static void blk_alloc(struct XenDevice *xendev)
 
     blkdev->ctx = iothread_get_aio_context(blkdev->iothread);
     blkdev->bh = aio_bh_new(blkdev->ctx, blk_bh, blkdev);
-
-    if (xen_mode != XEN_EMULATE) {
-        batch_maps = 1;
-    }
 }
 
 static void blk_parse_discard(struct XenBlkDev *blkdev)
@@ -981,15 +737,10 @@ static int blk_init(struct XenDevice *xendev)
 
     blkdev->file_blk  = BLOCK_SIZE;
 
-    xen_pv_printf(&blkdev->xendev, 3, "grant copy operation %s\n",
-                  xen_feature_grant_copy ? "enabled" : "disabled");
-
     /* fill info
      * blk_connect supplies sector-size and sectors
      */
     xenstore_write_be_int(&blkdev->xendev, "feature-flush-cache", 1);
-    xenstore_write_be_int(&blkdev->xendev, "feature-persistent",
-                          !xen_feature_grant_copy);
     xenstore_write_be_int(&blkdev->xendev, "info", info);
 
     xenstore_write_be_int(&blkdev->xendev, "max-ring-page-order",
@@ -1016,19 +767,10 @@ out_error:
     return -1;
 }
 
-/*
- * We need to account for the grant allocations requiring contiguous
- * chunks; the worst case number would be
- *     max_req * max_seg + (max_req - 1) * (max_seg - 1) + 1,
- * but in order to keep things simple just use
- *     2 * max_req * max_seg.
- */
-#define MAX_GRANTS(max_req, max_seg) (2 * (max_req) * (max_seg))
-
 static int blk_connect(struct XenDevice *xendev)
 {
     struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
-    int pers, index, qflags;
+    int index, qflags;
     bool readonly = true;
     bool writethrough = true;
     int order, ring_ref;
@@ -1150,11 +892,6 @@ static int blk_connect(struct XenDevice *xendev)
                              &blkdev->xendev.remote_port) == -1) {
         return -1;
     }
-    if (xenstore_read_fe_int(&blkdev->xendev, "feature-persistent", &pers)) {
-        blkdev->feature_persistent = FALSE;
-    } else {
-        blkdev->feature_persistent = !!pers;
-    }
 
     if (!blkdev->xendev.protocol) {
         blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
@@ -1189,11 +926,8 @@ static int blk_connect(struct XenDevice *xendev)
         return -1;
     }
 
-    /* Calculate the maximum number of grants needed by ioreqs */
-    max_grants = MAX_GRANTS(blkdev->max_requests,
-                            BLKIF_MAX_SEGMENTS_PER_REQUEST);
     /* Add on the number needed for the ring pages */
-    max_grants += blkdev->nr_ring_ref;
+    max_grants = blkdev->nr_ring_ref;
 
     xen_be_set_max_grant_refs(xendev, max_grants);
 
@@ -1204,8 +938,6 @@ static int blk_connect(struct XenDevice *xendev)
         return -1;
     }
 
-    blkdev->cnt_map++;
-
     switch (blkdev->protocol) {
     case BLKIF_PROTOCOL_NATIVE:
     {
@@ -1229,19 +961,6 @@ static int blk_connect(struct XenDevice *xendev)
     }
     }
 
-    if (blkdev->feature_persistent) {
-        /* Init persistent grants */
-        blkdev->max_grants = blkdev->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;
-    }
-
     blk_set_aio_context(blkdev->blk, blkdev->ctx);
 
     xen_be_bind_evtchn(&blkdev->xendev);
@@ -1274,29 +993,8 @@ static void blk_disconnect(struct XenDevice *xendev)
     if (blkdev->sring) {
         xen_be_unmap_grant_refs(xendev, blkdev->sring,
                                 blkdev->nr_ring_ref);
-        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)
-- 
1.9.1