Re: superpages lost after migration of HVM domU

[Olaf Hering <olaf@aepfle.de>]

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On Thu, Apr 20, Jan Beulich wrote:

> >>> On 20.04.17 at 18:04, <olaf@aepfle.de> wrote:
> > On Thu, Apr 20, Andrew Cooper wrote:
> > 
> >> As it currently stands, the sending side iterates from 0 to p2m_size,
> >> and sends every frame on the first pass.  This means we get PAGE_DATA
> >> records linearly, in batches of 1024, or two aligned 2M superpages.
> > Is there a way to preserve 1G pages? This 380G domU I'm looking at is
> > built with 4k:461390 2M:2341 1G:365 pages.
> I think we've hashed out a possible way to deal with this, by
> speculatively allocating 1G pages as long as the allocation cap for
> the domain allows, subsequently punching holes into those pages
> if we can't allocate any new pages anymore (due to otherwise
> overrunning the cap).

The result is not pretty. This HVM-only approach appears to work for a
domU with "memory=3024" and localhost migration.
It is required to punch holes as soon as possible to avoid errors in
xenforeignmemory_map due to "Over-allocation". Would be nice if the
receiver gets a memory map upfront to avoid all stunts...

Olaf

diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
index a83f22af4e..36e7891dde 100644
--- a/tools/libxc/xc_sr_common.h
+++ b/tools/libxc/xc_sr_common.h
@@ -107,6 +107,9 @@ struct xc_sr_save_ops
  */
 struct xc_sr_restore_ops
 {
+    /* Allocate a MFN for the given PFN */
+    int (*allocate_pfn)(struct xc_sr_context *ctx, xen_pfn_t pfn);
+
     /* Convert a PFN to GFN.  May return ~0UL for an invalid mapping. */
     xen_pfn_t (*pfn_to_gfn)(const struct xc_sr_context *ctx, xen_pfn_t pfn);
 
@@ -331,6 +334,14 @@ struct xc_sr_context
                     /* HVM context blob. */
                     void *context;
                     size_t contextsz;
+
+                    /* Bitmap of currently allocated PFNs during restore. */
+                    xen_pfn_t *sp_extents;
+                    unsigned long *attempted_1g;
+                    unsigned long *attempted_2m;
+                    unsigned long *allocated_pfns;
+                    xen_pfn_t max_allocated_pfn;
+                    unsigned long alloc_cnt;
                 } restore;
             };
         } x86_hvm;
diff --git a/tools/libxc/xc_sr_restore.c b/tools/libxc/xc_sr_restore.c
index 3549f0a1ae..2e8d15307f 100644
--- a/tools/libxc/xc_sr_restore.c
+++ b/tools/libxc/xc_sr_restore.c
@@ -135,6 +135,7 @@ 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 min_pfn = original_pfns[0], max_pfn = original_pfns[0];
     xen_pfn_t *mfns = malloc(count * sizeof(*mfns)),
         *pfns = malloc(count * sizeof(*pfns));
     unsigned i, nr_pfns = 0;
@@ -149,11 +150,18 @@ int populate_pfns(struct xc_sr_context *ctx, unsigned count,
 
     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];
         if ( (!types || (types &&
                          (types[i] != XEN_DOMCTL_PFINFO_XTAB &&
                           types[i] != XEN_DOMCTL_PFINFO_BROKEN))) &&
              !pfn_is_populated(ctx, original_pfns[i]) )
         {
+            rc = ctx->restore.ops.allocate_pfn(ctx, original_pfns[i]);
+            if ( rc )
+                goto err;
             rc = pfn_set_populated(ctx, original_pfns[i]);
             if ( rc )
                 goto err;
@@ -161,6 +169,16 @@ int populate_pfns(struct xc_sr_context *ctx, unsigned count,
             ++nr_pfns;
         }
     }
+    IPRINTF("checking range %lx %lx\n", min_pfn, max_pfn);
+    while (min_pfn < max_pfn) {
+        if (!pfn_is_populated(ctx, min_pfn) && test_and_clear_bit(min_pfn, ctx->x86_hvm.restore.allocated_pfns)) {
+            xen_pfn_t pfn = min_pfn;
+            rc = xc_domain_decrease_reservation_exact(xch, ctx->domid, 1, 0, &pfn);
+            IPRINTF("free %lx %lx %d\n", min_pfn, pfn, rc);
+        }
+        min_pfn++;
+    }
+    nr_pfns = 0;
 
     if ( nr_pfns )
     {
@@ -723,6 +741,10 @@ static void cleanup(struct xc_sr_context *ctx)
                                    NRPAGES(bitmap_size(ctx->restore.p2m_size)));
     free(ctx->restore.buffered_records);
     free(ctx->restore.populated_pfns);
+    free(ctx->x86_hvm.restore.sp_extents);
+    free(ctx->x86_hvm.restore.attempted_1g);
+    free(ctx->x86_hvm.restore.attempted_2m);
+    free(ctx->x86_hvm.restore.allocated_pfns);
     if ( ctx->restore.ops.cleanup(ctx) )
         PERROR("Failed to clean up");
 }
@@ -810,6 +832,17 @@ static int restore(struct xc_sr_context *ctx)
     saved_errno = errno;
     saved_rc = rc;
     PERROR("Restore failed");
+    {
+        unsigned long i;
+        bool a, p;
+        IPRINTF("alloc_cnt %lu\n", ctx->x86_hvm.restore.alloc_cnt);
+        for (i = 0; i < ctx->restore.p2m_size; i++) {
+            p = test_bit(i, ctx->restore.populated_pfns);
+            a = test_bit(i, ctx->x86_hvm.restore.allocated_pfns);
+            if (p != a)
+                IPRINTF("%lx a %x p %x\n", i, a, p);
+        }
+    }
 
  done:
     cleanup(ctx);
@@ -888,6 +921,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
     }
 
     ctx.restore.p2m_size = nr_pfns;
+    IPRINTF("p2m_size %lx\n", ctx.restore.p2m_size);
 
     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..fc441d2a6d 100644
--- a/tools/libxc/xc_sr_restore_x86_hvm.c
+++ b/tools/libxc/xc_sr_restore_x86_hvm.c
@@ -3,6 +3,10 @@
 
 #include "xc_sr_common_x86.h"
 
+#define SUPERPAGE_2MB_SHIFT   9
+#define SUPERPAGE_2MB_NR_PFNS (1UL << SUPERPAGE_2MB_SHIFT)
+#define SUPERPAGE_1GB_SHIFT   18
+#define SUPERPAGE_1GB_NR_PFNS (1UL << SUPERPAGE_1GB_SHIFT)
 /*
  * Process an HVM_CONTEXT record from the stream.
  */
@@ -149,6 +153,20 @@ static int x86_hvm_setup(struct xc_sr_context *ctx)
         return -1;
     }
 
+    ctx->x86_hvm.restore.sp_extents = calloc(1UL << SUPERPAGE_1GB_SHIFT, sizeof(*ctx->x86_hvm.restore.sp_extents));
+    ctx->x86_hvm.restore.attempted_1g = bitmap_alloc((ctx->restore.p2m_size >> SUPERPAGE_1GB_SHIFT) + 1);
+    ctx->x86_hvm.restore.attempted_2m = bitmap_alloc((ctx->restore.p2m_size >> SUPERPAGE_2MB_SHIFT) + 1);
+    ctx->x86_hvm.restore.max_allocated_pfn = ctx->restore.p2m_size;
+    ctx->x86_hvm.restore.allocated_pfns = bitmap_alloc(ctx->x86_hvm.restore.max_allocated_pfn + 1);
+    if (!ctx->x86_hvm.restore.sp_extents || !ctx->x86_hvm.restore.allocated_pfns || !ctx->x86_hvm.restore.attempted_2m || !ctx->x86_hvm.restore.attempted_1g)
+    {
+        ERROR("Unable to allocate memory for allocated_pfns bitmaps");
+        return -1;
+    }
+    /* No superpage in 1st 2MB due to VGA hole */
+    set_bit(0, ctx->x86_hvm.restore.attempted_1g);
+    set_bit(0, ctx->x86_hvm.restore.attempted_2m);
+
     return 0;
 }
 
@@ -228,8 +246,139 @@ static int x86_hvm_cleanup(struct xc_sr_context *ctx)
     return 0;
 }
 
+static bool pfn_is_allocated(const struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    if ( pfn > ctx->x86_hvm.restore.max_allocated_pfn )
+        return false;
+    return test_bit(pfn, ctx->x86_hvm.restore.allocated_pfns);
+}
+
+/*
+ * Set a pfn as allocated, expanding the tracking structures if needed. To
+ * avoid realloc()ing too excessively, the size increased to the nearest power
+ * of two large enough to contain the required pfn.
+ */
+static int pfn_set_allocated(struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    xc_interface *xch = ctx->xch;
+
+    if ( pfn > ctx->x86_hvm.restore.max_allocated_pfn )
+    {
+        xen_pfn_t new_max;
+        size_t old_sz, new_sz;
+        unsigned long *p;
+
+        /* Round up to the nearest power of two larger than pfn, less 1. */
+        new_max = pfn;
+        new_max |= new_max >> 1;
+        new_max |= new_max >> 2;
+        new_max |= new_max >> 4;
+        new_max |= new_max >> 8;
+        new_max |= new_max >> 16;
+#ifdef __x86_64__
+        new_max |= new_max >> 32;
+#endif
+
+        old_sz = bitmap_size(ctx->x86_hvm.restore.max_allocated_pfn + 1);
+        new_sz = bitmap_size(new_max + 1);
+        p = realloc(ctx->x86_hvm.restore.allocated_pfns, new_sz);
+        if ( !p )
+        {
+            ERROR("Failed to realloc allocated bitmap");
+            errno = ENOMEM;
+            return -1;
+        }
+
+        memset((uint8_t *)p + old_sz, 0x00, new_sz - old_sz);
+
+        ctx->x86_hvm.restore.allocated_pfns    = p;
+        ctx->x86_hvm.restore.max_allocated_pfn = new_max;
+    }
+
+    assert(!test_bit(pfn, ctx->x86_hvm.restore.allocated_pfns));
+    set_bit(pfn, ctx->x86_hvm.restore.allocated_pfns);
+
+    return 0;
+}
+
+static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    xc_interface *xch = ctx->xch;
+    bool success = false;
+    int rc = -1;
+    long done;
+    unsigned long i, nr_extents;
+    unsigned long stat_1g = 0, stat_2m = 0, stat_4k = 0;
+    unsigned long idx_1g, idx_2m;
+    unsigned long count;
+    xen_pfn_t base_pfn = 0, *sp_extents = ctx->x86_hvm.restore.sp_extents;
+
+    IPRINTF("pfn %lx\n", (long)pfn);
+    if (pfn_is_allocated(ctx, pfn))
+        return 0;
+
+    idx_1g = pfn >> SUPERPAGE_1GB_SHIFT;
+    idx_2m = pfn >> SUPERPAGE_2MB_SHIFT;
+    IPRINTF("idx_1g %lu idx_2m %lu\n", idx_1g, idx_2m);
+    if (!test_and_set_bit(idx_1g, ctx->x86_hvm.restore.attempted_1g)) {
+        count = 1UL << SUPERPAGE_1GB_SHIFT;
+        base_pfn = (pfn >> SUPERPAGE_1GB_SHIFT) << SUPERPAGE_1GB_SHIFT;
+        nr_extents = count >> SUPERPAGE_1GB_SHIFT;
+        IPRINTF("base_pfn %lx count %lu nr_extents %lu\n", (long)base_pfn, count, nr_extents);
+        for ( i = 0; i < nr_extents; i++ )
+            sp_extents[i] = base_pfn + (i<<SUPERPAGE_1GB_SHIFT);
+        done = xc_domain_populate_physmap(xch, ctx->domid, nr_extents, SUPERPAGE_1GB_SHIFT, 0, sp_extents);
+        IPRINTF("1G %lu -> %ld\n", nr_extents, done);
+        if (done > 0) {
+            success = true;
+            ctx->x86_hvm.restore.alloc_cnt += count;
+            stat_1g = done;
+            for (i = 0; i < (count >> SUPERPAGE_2MB_SHIFT); i++)
+                set_bit((base_pfn >> SUPERPAGE_2MB_SHIFT) + i, ctx->x86_hvm.restore.attempted_2m);
+        }
+    }
+
+    if (!test_and_set_bit(idx_2m, ctx->x86_hvm.restore.attempted_2m)) {
+        count = 1UL << SUPERPAGE_2MB_SHIFT;
+        base_pfn = (pfn >> SUPERPAGE_2MB_SHIFT) << SUPERPAGE_2MB_SHIFT;
+        nr_extents = count >> SUPERPAGE_2MB_SHIFT;
+        IPRINTF("base_pfn %lx count %lu nr_extents %lu\n", (long)base_pfn, count, nr_extents);
+        for ( i = 0; i < nr_extents; i++ )
+            sp_extents[i] = base_pfn + (i<<SUPERPAGE_2MB_SHIFT);
+        done = xc_domain_populate_physmap(xch, ctx->domid, nr_extents, SUPERPAGE_2MB_SHIFT, 0, sp_extents);
+        IPRINTF("2M %lu -> %ld\n", nr_extents, done);
+        if (done > 0) {
+            success = true;
+            ctx->x86_hvm.restore.alloc_cnt += count;
+            stat_2m = done;
+        }
+    }
+    if (success == false) {
+        count = 1;
+        sp_extents[0] = base_pfn = pfn;
+        done = xc_domain_populate_physmap(xch, ctx->domid, count, 0, 0, sp_extents);
+        if (done > 0) {
+            success = true;
+            ctx->x86_hvm.restore.alloc_cnt += count;
+            stat_4k = count;
+        }
+    }
+    IPRINTF("count %lu\n", count);
+    IPRINTF("1G %lu 2M %lu 4k %lu\n", stat_1g, stat_2m, stat_4k);
+    if (success == true) {
+        do {
+            count--;
+            rc = pfn_set_allocated(ctx, base_pfn + count);
+            if (rc)
+                break;
+        } while (count);
+    }
+    return rc;
+}
+
 struct xc_sr_restore_ops restore_ops_x86_hvm =
 {
+    .allocate_pfn    = x86_hvm_allocate_pfn,
     .pfn_is_valid    = x86_hvm_pfn_is_valid,
     .pfn_to_gfn      = x86_hvm_pfn_to_gfn,
     .set_gfn         = x86_hvm_set_gfn,
diff --git a/tools/libxc/xc_sr_restore_x86_pv.c b/tools/libxc/xc_sr_restore_x86_pv.c
index 50e25c162c..c426f14c73 100644
--- a/tools/libxc/xc_sr_restore_x86_pv.c
+++ b/tools/libxc/xc_sr_restore_x86_pv.c
@@ -1152,8 +1152,15 @@ static int x86_pv_cleanup(struct xc_sr_context *ctx)
     return 0;
 }
 
+static int x86_pv_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
+{
+    errno = ENOMEM;
+    return -1;
+}
+
 struct xc_sr_restore_ops restore_ops_x86_pv =
 {
+    .allocate_pfn    = x86_pv_allocate_pfn,
     .pfn_is_valid    = x86_pv_pfn_is_valid,
     .pfn_to_gfn      = pfn_to_mfn,
     .set_page_type   = x86_pv_set_page_type,

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