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[Xen-devel] [PATCH v6 3/3] tools/libxc: use superpages during restore of HVM guest



During creating of a HVM domU meminit_hvm() tries to map superpages.
After save/restore or migration this mapping is lost, everything is
allocated in single pages. This causes a performance degradition after
migration.

Add neccessary code to preallocate a superpage for the chunk of pfns
that is received. In case a pfn was not populated on the sending side it
must be freed on the receiving side to avoid over-allocation.

The existing code for x86_pv is moved unmodified into its own file.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libxc/xc_sr_common.h          |  25 +++-
 tools/libxc/xc_sr_restore.c         |  75 +---------
 tools/libxc/xc_sr_restore_x86_hvm.c | 288 ++++++++++++++++++++++++++++++++++++
 tools/libxc/xc_sr_restore_x86_pv.c  |  72 ++++++++-
 4 files changed, 382 insertions(+), 78 deletions(-)

diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
index da2691ba79..0fa0fbea4d 100644
--- a/tools/libxc/xc_sr_common.h
+++ b/tools/libxc/xc_sr_common.h
@@ -139,6 +139,16 @@ struct xc_sr_restore_ops
      */
     int (*setup)(struct xc_sr_context *ctx);
 
+    /**
+     * Populate PFNs
+     *
+     * Given a set of pfns, obtain memory from Xen to fill the physmap for the
+     * unpopulated subset.
+     */
+    int (*populate_pfns)(struct xc_sr_context *ctx, unsigned count,
+                         const xen_pfn_t *original_pfns, const uint32_t 
*types);
+
+
     /**
      * Process an individual record from the stream.  The caller shall take
      * care of processing common records (e.g. END, PAGE_DATA).
@@ -224,6 +234,8 @@ struct xc_sr_context
 
             int send_back_fd;
             unsigned long p2m_size;
+            unsigned long max_pages;
+            unsigned long tot_pages;
             xc_hypercall_buffer_t dirty_bitmap_hbuf;
 
             /* From Image Header. */
@@ -336,6 +348,11 @@ struct xc_sr_context
                     /* HVM context blob. */
                     void *context;
                     size_t contextsz;
+
+                    /* Bitmap of currently allocated PFNs during restore. */
+                    struct xc_sr_bitmap attempted_1g;
+                    struct xc_sr_bitmap attempted_2m;
+                    struct xc_sr_bitmap allocated_pfns;
                 } restore;
             };
         } x86_hvm;
@@ -455,14 +472,6 @@ static inline int write_record(struct xc_sr_context *ctx,
  */
 int read_record(struct xc_sr_context *ctx, int fd, struct xc_sr_record *rec);
 
-/*
- * This would ideally be private in restore.c, but is needed by
- * x86_pv_localise_page() if we receive pagetables frames ahead of the
- * contents of the frames they point at.
- */
-int populate_pfns(struct xc_sr_context *ctx, unsigned count,
-                  const xen_pfn_t *original_pfns, const uint32_t *types);
-
 #endif
 /*
  * Local variables:
diff --git a/tools/libxc/xc_sr_restore.c b/tools/libxc/xc_sr_restore.c
index d53948e1a6..8cd9289d1a 100644
--- a/tools/libxc/xc_sr_restore.c
+++ b/tools/libxc/xc_sr_restore.c
@@ -68,74 +68,6 @@ static int read_headers(struct xc_sr_context *ctx)
     return 0;
 }
 
-/*
- * Given a set of pfns, obtain memory from Xen to fill the physmap for the
- * unpopulated subset.  If types is NULL, no page type checking is performed
- * and all unpopulated pfns are populated.
- */
-int populate_pfns(struct xc_sr_context *ctx, unsigned count,
-                  const xen_pfn_t *original_pfns, const uint32_t *types)
-{
-    xc_interface *xch = ctx->xch;
-    xen_pfn_t *mfns = malloc(count * sizeof(*mfns)),
-        *pfns = malloc(count * sizeof(*pfns));
-    unsigned i, nr_pfns = 0;
-    int rc = -1;
-
-    if ( !mfns || !pfns )
-    {
-        ERROR("Failed to allocate %zu bytes for populating the physmap",
-              2 * count * sizeof(*mfns));
-        goto err;
-    }
-
-    for ( i = 0; i < count; ++i )
-    {
-        if ( (!types || (types &&
-                         (types[i] != XEN_DOMCTL_PFINFO_XTAB &&
-                          types[i] != XEN_DOMCTL_PFINFO_BROKEN))) &&
-             !pfn_is_populated(ctx, original_pfns[i]) )
-        {
-            rc = pfn_set_populated(ctx, original_pfns[i]);
-            if ( rc )
-                goto err;
-            pfns[nr_pfns] = mfns[nr_pfns] = original_pfns[i];
-            ++nr_pfns;
-        }
-    }
-
-    if ( nr_pfns )
-    {
-        rc = xc_domain_populate_physmap_exact(
-            xch, ctx->domid, nr_pfns, 0, 0, mfns);
-        if ( rc )
-        {
-            PERROR("Failed to populate physmap");
-            goto err;
-        }
-
-        for ( i = 0; i < nr_pfns; ++i )
-        {
-            if ( mfns[i] == INVALID_MFN )
-            {
-                ERROR("Populate physmap failed for pfn %u", i);
-                rc = -1;
-                goto err;
-            }
-
-            ctx->restore.ops.set_gfn(ctx, pfns[i], mfns[i]);
-        }
-    }
-
-    rc = 0;
-
- err:
-    free(pfns);
-    free(mfns);
-
-    return rc;
-}
-
 /*
  * Given a list of pfns, their types, and a block of page data from the
  * stream, populate and record their types, map the relevant subset and copy
@@ -161,7 +93,7 @@ static int process_page_data(struct xc_sr_context *ctx, 
unsigned count,
         goto err;
     }
 
-    rc = populate_pfns(ctx, count, pfns, types);
+    rc = ctx->restore.ops.populate_pfns(ctx, count, pfns, types);
     if ( rc )
     {
         ERROR("Failed to populate pfns for batch of %u pages", count);
@@ -826,7 +758,12 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
uint32_t dom,
         return -1;
     }
 
+    /* See xc_domain_getinfo */
+    ctx.restore.max_pages = ctx.dominfo.max_memkb >> (PAGE_SHIFT-10);
+    ctx.restore.tot_pages = ctx.dominfo.nr_pages;
     ctx.restore.p2m_size = nr_pfns;
+    DPRINTF("dom %u p2m_size %lx max_pages %lx",
+            ctx.domid, ctx.restore.p2m_size, ctx.restore.max_pages);
 
     if ( ctx.dominfo.hvm )
     {
diff --git a/tools/libxc/xc_sr_restore_x86_hvm.c 
b/tools/libxc/xc_sr_restore_x86_hvm.c
index 1dca85354a..2b0eca0c7c 100644
--- a/tools/libxc/xc_sr_restore_x86_hvm.c
+++ b/tools/libxc/xc_sr_restore_x86_hvm.c
@@ -135,6 +135,8 @@ static int x86_hvm_localise_page(struct xc_sr_context *ctx,
 static int x86_hvm_setup(struct xc_sr_context *ctx)
 {
     xc_interface *xch = ctx->xch;
+    struct xc_sr_bitmap *bm;
+    unsigned long bits;
 
     if ( ctx->restore.guest_type != DHDR_TYPE_X86_HVM )
     {
@@ -149,7 +151,30 @@ static int x86_hvm_setup(struct xc_sr_context *ctx)
         return -1;
     }
 
+    bm = &ctx->x86_hvm.restore.attempted_1g;
+    bits = (ctx->restore.p2m_size >> SUPERPAGE_1GB_SHIFT) + 1;
+    if ( xc_sr_bitmap_resize(bm, bits) == false )
+        goto out;
+
+    bm = &ctx->x86_hvm.restore.attempted_2m;
+    bits = (ctx->restore.p2m_size >> SUPERPAGE_2MB_SHIFT) + 1;
+    if ( xc_sr_bitmap_resize(bm, bits) == false )
+        goto out;
+
+    bm = &ctx->x86_hvm.restore.allocated_pfns;
+    bits = ctx->restore.p2m_size + 1;
+    if ( xc_sr_bitmap_resize(bm, bits) == false )
+        goto out;
+
+    /* No superpage in 1st 2MB due to VGA hole */
+    xc_sr_set_bit(0, &ctx->x86_hvm.restore.attempted_1g);
+    xc_sr_set_bit(0, &ctx->x86_hvm.restore.attempted_2m);
+
     return 0;
+
+out:
+    ERROR("Unable to allocate memory for pfn bitmaps");
+    return -1;
 }
 
 /*
@@ -224,10 +249,272 @@ static int x86_hvm_stream_complete(struct xc_sr_context 
*ctx)
 static int x86_hvm_cleanup(struct xc_sr_context *ctx)
 {
     free(ctx->x86_hvm.restore.context);
+    xc_sr_bitmap_free(&ctx->x86_hvm.restore.attempted_1g);
+    xc_sr_bitmap_free(&ctx->x86_hvm.restore.attempted_2m);
+    xc_sr_bitmap_free(&ctx->x86_hvm.restore.allocated_pfns);
 
     return 0;
 }
 
+/*
+ * Set a pfn as allocated, expanding the tracking structures if needed.
+ */
+static int pfn_set_allocated(struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    xc_interface *xch = ctx->xch;
+
+    if ( !xc_sr_set_bit(pfn, &ctx->x86_hvm.restore.allocated_pfns) )
+    {
+        ERROR("Failed to realloc allocated_pfns bitmap");
+        errno = ENOMEM;
+        return -1;
+    }
+    return 0;
+}
+
+struct x86_hvm_sp {
+    xen_pfn_t pfn;
+    xen_pfn_t base_pfn;
+    unsigned long index;
+    unsigned long count;
+};
+
+/*
+ * Try to allocate a 1GB page for this pfn, but avoid Over-allocation.
+ * If this succeeds, mark the range of 2MB pages as busy.
+ */
+static bool x86_hvm_alloc_1g(struct xc_sr_context *ctx, struct x86_hvm_sp *sp)
+{
+    xc_interface *xch = ctx->xch;
+    struct xc_sr_bitmap *bm;
+    unsigned int order, shift;
+    int i, done;
+    xen_pfn_t extent;
+
+    bm = &ctx->x86_hvm.restore.attempted_1g;
+
+    /* Only one attempt to avoid overlapping allocation */
+    if ( xc_sr_test_and_set_bit(sp->index, bm) )
+        return false;
+
+    order = SUPERPAGE_1GB_SHIFT;
+    sp->count = 1ULL << order;
+
+    /* Allocate only if there is room for another superpage */
+    if ( ctx->restore.tot_pages + sp->count > ctx->restore.max_pages )
+        return false;
+
+    extent = sp->base_pfn = (sp->pfn >> order) << order;
+    done = xc_domain_populate_physmap(xch, ctx->domid, 1, order, 0, &extent);
+    if ( done < 0 ) {
+        PERROR("populate_physmap failed.");
+        return false;
+    }
+    if ( done == 0 )
+        return false;
+
+    DPRINTF("1G base_pfn %" PRI_xen_pfn "\n", sp->base_pfn);
+
+    /* Mark all 2MB pages as done to avoid overlapping allocation */
+    bm = &ctx->x86_hvm.restore.attempted_2m;
+    shift = SUPERPAGE_1GB_SHIFT - SUPERPAGE_2MB_SHIFT;
+    for ( i = 0; i < (sp->count >> shift); i++ )
+        xc_sr_set_bit((sp->base_pfn >> SUPERPAGE_2MB_SHIFT) + i, bm);
+
+    return true;
+}
+
+/* Allocate a 2MB page if x86_hvm_alloc_1g failed, avoid Over-allocation. */
+static bool x86_hvm_alloc_2m(struct xc_sr_context *ctx, struct x86_hvm_sp *sp)
+{
+    xc_interface *xch = ctx->xch;
+    struct xc_sr_bitmap *bm;
+    unsigned int order;
+    int done;
+    xen_pfn_t extent;
+
+    bm = &ctx->x86_hvm.restore.attempted_2m;
+
+    /* Only one attempt to avoid overlapping allocation */
+    if ( xc_sr_test_and_set_bit(sp->index, bm) )
+        return false;
+
+    order = SUPERPAGE_2MB_SHIFT;
+    sp->count = 1ULL << order;
+
+    /* Allocate only if there is room for another superpage */
+    if ( ctx->restore.tot_pages + sp->count > ctx->restore.max_pages )
+        return false;
+
+    extent = sp->base_pfn = (sp->pfn >> order) << order;
+    done = xc_domain_populate_physmap(xch, ctx->domid, 1, order, 0, &extent);
+    if ( done < 0 ) {
+        PERROR("populate_physmap failed.");
+        return false;
+    }
+    if ( done == 0 )
+        return false;
+
+    DPRINTF("2M base_pfn %" PRI_xen_pfn "\n", sp->base_pfn);
+    return true;
+}
+
+/* Allocate a single page if x86_hvm_alloc_2m failed. */
+static bool x86_hvm_alloc_4k(struct xc_sr_context *ctx, struct x86_hvm_sp *sp)
+{
+    xc_interface *xch = ctx->xch;
+    unsigned int order;
+    int done;
+    xen_pfn_t extent;
+
+    order = 0;
+    sp->count = 1ULL << order;
+
+    /* Allocate only if there is room for another page */
+    if ( ctx->restore.tot_pages + sp->count > ctx->restore.max_pages )
+        return false;
+
+    extent = sp->base_pfn = (sp->pfn >> order) << order;
+    done = xc_domain_populate_physmap(xch, ctx->domid, 1, order, 0, &extent);
+    if ( done < 0 ) {
+        PERROR("populate_physmap failed.");
+        return false;
+    }
+    if ( done == 0 )
+        return false;
+
+    DPRINTF("4K base_pfn %" PRI_xen_pfn "\n", sp->base_pfn);
+    return true;
+}
+/*
+ * Attempt to allocate a superpage where the pfn resides.
+ */
+static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    xc_interface *xch = ctx->xch;
+    bool success;
+    int rc = -1;
+    unsigned long idx_1g, idx_2m;
+    struct x86_hvm_sp sp = {
+        .pfn = pfn
+    };
+
+    if ( xc_sr_test_bit(pfn, &ctx->x86_hvm.restore.allocated_pfns) )
+        return 0;
+
+    idx_1g = pfn >> SUPERPAGE_1GB_SHIFT;
+    idx_2m = pfn >> SUPERPAGE_2MB_SHIFT;
+    if ( !xc_sr_bitmap_resize(&ctx->x86_hvm.restore.attempted_1g, idx_1g) )
+    {
+        PERROR("Failed to realloc attempted_1g");
+        return -1;
+    }
+    if ( !xc_sr_bitmap_resize(&ctx->x86_hvm.restore.attempted_2m, idx_2m) )
+    {
+        PERROR("Failed to realloc attempted_2m");
+        return -1;
+    }
+
+    sp.index = idx_1g;
+    success = x86_hvm_alloc_1g(ctx, &sp);
+
+    if ( success == false ) {
+        sp.index = idx_2m;
+        success = x86_hvm_alloc_2m(ctx, &sp);
+    }
+
+    if ( success == false ) {
+        sp.index = 0;
+        success = x86_hvm_alloc_4k(ctx, &sp);
+    }
+
+    if ( success == true ) {
+        do {
+            sp.count--;
+            ctx->restore.tot_pages++;
+            rc = pfn_set_allocated(ctx, sp.base_pfn + sp.count);
+            if ( rc )
+                break;
+        } while ( sp.count );
+    }
+    return rc;
+}
+
+static int x86_hvm_populate_pfns(struct xc_sr_context *ctx, unsigned count,
+                                 const xen_pfn_t *original_pfns,
+                                 const uint32_t *types)
+{
+    xc_interface *xch = ctx->xch;
+    xen_pfn_t pfn, min_pfn = original_pfns[0], max_pfn = original_pfns[0];
+    unsigned i, freed = 0, order;
+    int rc = -1;
+
+    for ( i = 0; i < count; ++i )
+    {
+        if ( original_pfns[i] < min_pfn )
+            min_pfn = original_pfns[i];
+        if ( original_pfns[i] > max_pfn )
+            max_pfn = original_pfns[i];
+    }
+    DPRINTF("batch of %u pfns between %" PRI_xen_pfn " %" PRI_xen_pfn "\n",
+            count, min_pfn, max_pfn);
+
+    for ( i = 0; i < count; ++i )
+    {
+        if ( (types[i] != XEN_DOMCTL_PFINFO_XTAB &&
+              types[i] != XEN_DOMCTL_PFINFO_BROKEN) &&
+             !pfn_is_populated(ctx, original_pfns[i]) )
+        {
+            rc = x86_hvm_allocate_pfn(ctx, original_pfns[i]);
+            if ( rc )
+                goto err;
+            rc = pfn_set_populated(ctx, original_pfns[i]);
+            if ( rc )
+                goto err;
+        }
+    }
+
+    /*
+     * Scan the entire superpage because several batches will fit into
+     * a superpage, and it is unknown which pfn triggered the allocation.
+     */
+    order = SUPERPAGE_1GB_SHIFT;
+    pfn = min_pfn = (min_pfn >> order) << order;
+
+    while ( pfn <= max_pfn )
+    {
+        struct xc_sr_bitmap *bm;
+        bm = &ctx->x86_hvm.restore.allocated_pfns;
+        if ( !xc_sr_bitmap_resize(bm, pfn) )
+        {
+            PERROR("Failed to realloc allocated_pfns %" PRI_xen_pfn, pfn);
+            goto err;
+        }
+        if ( !pfn_is_populated(ctx, pfn) &&
+            xc_sr_test_and_clear_bit(pfn, bm) ) {
+            xen_pfn_t p = pfn;
+            rc = xc_domain_decrease_reservation_exact(xch, ctx->domid, 1, 0, 
&p);
+            if ( rc )
+            {
+                PERROR("Failed to release pfn %" PRI_xen_pfn, pfn);
+                goto err;
+            }
+            ctx->restore.tot_pages--;
+            freed++;
+        }
+        pfn++;
+    }
+    if ( freed )
+        DPRINTF("freed %u between %" PRI_xen_pfn " %" PRI_xen_pfn "\n",
+                freed, min_pfn, max_pfn);
+
+    rc = 0;
+
+ err:
+    return rc;
+}
+
+
 struct xc_sr_restore_ops restore_ops_x86_hvm =
 {
     .pfn_is_valid    = x86_hvm_pfn_is_valid,
@@ -236,6 +523,7 @@ struct xc_sr_restore_ops restore_ops_x86_hvm =
     .set_page_type   = x86_hvm_set_page_type,
     .localise_page   = x86_hvm_localise_page,
     .setup           = x86_hvm_setup,
+    .populate_pfns   = x86_hvm_populate_pfns,
     .process_record  = x86_hvm_process_record,
     .stream_complete = x86_hvm_stream_complete,
     .cleanup         = x86_hvm_cleanup,
diff --git a/tools/libxc/xc_sr_restore_x86_pv.c 
b/tools/libxc/xc_sr_restore_x86_pv.c
index 50e25c162c..87957559bc 100644
--- a/tools/libxc/xc_sr_restore_x86_pv.c
+++ b/tools/libxc/xc_sr_restore_x86_pv.c
@@ -936,6 +936,75 @@ static void x86_pv_set_gfn(struct xc_sr_context *ctx, 
xen_pfn_t pfn,
         ((uint32_t *)ctx->x86_pv.p2m)[pfn] = mfn;
 }
 
+/*
+ * Given a set of pfns, obtain memory from Xen to fill the physmap for the
+ * unpopulated subset.  If types is NULL, no page type checking is performed
+ * and all unpopulated pfns are populated.
+ */
+static int x86_pv_populate_pfns(struct xc_sr_context *ctx, unsigned count,
+                                const xen_pfn_t *original_pfns,
+                                const uint32_t *types)
+{
+    xc_interface *xch = ctx->xch;
+    xen_pfn_t *mfns = malloc(count * sizeof(*mfns)),
+        *pfns = malloc(count * sizeof(*pfns));
+    unsigned i, nr_pfns = 0;
+    int rc = -1;
+
+    if ( !mfns || !pfns )
+    {
+        ERROR("Failed to allocate %zu bytes for populating the physmap",
+              2 * count * sizeof(*mfns));
+        goto err;
+    }
+
+    for ( i = 0; i < count; ++i )
+    {
+        if ( (!types || (types &&
+                         (types[i] != XEN_DOMCTL_PFINFO_XTAB &&
+                          types[i] != XEN_DOMCTL_PFINFO_BROKEN))) &&
+             !pfn_is_populated(ctx, original_pfns[i]) )
+        {
+            rc = pfn_set_populated(ctx, original_pfns[i]);
+            if ( rc )
+                goto err;
+            pfns[nr_pfns] = mfns[nr_pfns] = original_pfns[i];
+            ++nr_pfns;
+        }
+    }
+
+    if ( nr_pfns )
+    {
+        rc = xc_domain_populate_physmap_exact(
+            xch, ctx->domid, nr_pfns, 0, 0, mfns);
+        if ( rc )
+        {
+            PERROR("Failed to populate physmap");
+            goto err;
+        }
+
+        for ( i = 0; i < nr_pfns; ++i )
+        {
+            if ( mfns[i] == INVALID_MFN )
+            {
+                ERROR("Populate physmap failed for pfn %u", i);
+                rc = -1;
+                goto err;
+            }
+
+            ctx->restore.ops.set_gfn(ctx, pfns[i], mfns[i]);
+        }
+    }
+
+    rc = 0;
+
+ err:
+    free(pfns);
+    free(mfns);
+
+    return rc;
+}
+
 /*
  * restore_ops function.  Convert pfns back to mfns in pagetables.  Possibly
  * needs to populate new frames if a PTE is found referring to a frame which
@@ -980,7 +1049,7 @@ static int x86_pv_localise_page(struct xc_sr_context *ctx,
         }
     }
 
-    if ( to_populate && populate_pfns(ctx, to_populate, pfns, NULL) )
+    if ( to_populate && x86_pv_populate_pfns(ctx, to_populate, pfns, NULL) )
         return -1;
 
     for ( i = 0; i < (PAGE_SIZE / sizeof(uint64_t)); ++i )
@@ -1160,6 +1229,7 @@ struct xc_sr_restore_ops restore_ops_x86_pv =
     .set_gfn         = x86_pv_set_gfn,
     .localise_page   = x86_pv_localise_page,
     .setup           = x86_pv_setup,
+    .populate_pfns   = x86_pv_populate_pfns,
     .process_record  = x86_pv_process_record,
     .stream_complete = x86_pv_stream_complete,
     .cleanup         = x86_pv_cleanup,

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