Re: [Xen-devel] [PATCH v8 3/3] tools/libxc: use superpages during restore of HVM guest

[Olaf Hering]

On Fri, Sep 01, Olaf Hering wrote:

> +static int x86_hvm_populate_pfns(struct xc_sr_context *ctx, unsigned count,

> +/*
> + * If this next pfn is within another 1GB superpage it is 
> required
> + * to scan the entire previous superpage because there might be
> + * holes between max_pfn and the end of the superpage.
> + */
> +if ( idx1G_prev != idx1G )
> +{
> +order = SUPERPAGE_1GB_SHIFT;
> +max_pfn = (((max_pfn >> order) + 1) << order) - 1;
> +}
> +if ( x86_hvm_punch_hole(ctx, max_pfn) == false )


And thinking about this part: with this variant it is still possible
that Over-allocation happens. If the previous pfn was within a 2MB
range, and this pfn is in another 2MB range, then the hole after max_pfn
would not be covered. This part needs an 'else' with
SUPERPAGE_2MB_SHIFT.

This "reset to max" may trigger a bug in xc_sr_test_and_clear_bit(). It
has to check the size of the bitmap, just as xc_sr_test_bit() does.

Olaf


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[Xen-devel] [PATCH v8 3/3] tools/libxc: use superpages during restore of HVM guest

[Olaf Hering]

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 
---
 tools/libxc/xc_sr_common.h  |  25 ++-
 tools/libxc/xc_sr_restore.c |  75 +---
 tools/libxc/xc_sr_restore_x86_hvm.c | 337 
 tools/libxc/xc_sr_restore_x86_pv.c  |  72 +++-
 4 files changed, 431 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,