Re: [Xen-devel] [PATCH] libxc: fix memory leak in migration v2

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On July 24, 2015 6:40:27 PM EDT, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
>Originally there was only one counter to keep track of pages. It was
>used erroneously to keep track of how many pages were mapped and how
>many pages needed to be send. In the


sent

> end munmap(2) always has 0 as the
>length argument, which resulted in leaking the mapping.
>
>This problem is discovered on 32bit toolstack because 32bit application

/is/was/

>has notably smaller address space. In fact this bug affects 64bit
>toolstack too.

s/has/have/

>
>Use a separate counter to keep track of how many pages to send to solve
>this issue.
>
>Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>---
>Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
>Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>---
> tools/libxc/xc_sr_save.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
>diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
>index d63b783..bbcfeb6 100644
>--- a/tools/libxc/xc_sr_save.c
>+++ b/tools/libxc/xc_sr_save.c
>@@ -84,7 +84,7 @@ static int write_batch(struct xc_sr_context *ctx)
>     void **guest_data = NULL;
>     void **local_pages = NULL;
>     int *errors = NULL, rc = -1;
>-    unsigned i, p, nr_pages = 0;
>+    unsigned i, p, nr_pages = 0, nr_pages_to_send;
>     unsigned nr_pfns = ctx->save.nr_batch_pfns;
>     void *page, *orig_page;
>     uint64_t *rec_pfns = NULL;
>@@ -151,10 +151,12 @@ static int write_batch(struct xc_sr_context *ctx)
>         mfns[nr_pages++] = mfns[i];
>     }
> 
>-    if ( nr_pages > 0 )
>+    nr_pages_to_send = nr_pages;
>+
>+    if ( nr_pages_to_send > 0 )
>     {
>         guest_mapping = xc_map_foreign_bulk(
>-            xch, ctx->domid, PROT_READ, mfns, errors, nr_pages);
>+            xch, ctx->domid, PROT_READ, mfns, errors,
>nr_pages_to_send);
>         if ( !guest_mapping )
>         {
>             PERROR("Failed to map guest pages");
>@@ -191,7 +193,7 @@ static int write_batch(struct xc_sr_context *ctx)
>            set_bit(ctx->save.batch_pfns[i], ctx->save.deferred_pages);
>                     ++ctx->save.nr_deferred_pages;
>                     types[i] = XEN_DOMCTL_PFINFO_XTAB;
>-                    --nr_pages;
>+                    --nr_pages_to_send;
>                 }
>                 else
>                     goto err;
>@@ -216,7 +218,7 @@ static int write_batch(struct xc_sr_context *ctx)
> 
>     rec.length = sizeof(hdr);
>     rec.length += nr_pfns * sizeof(*rec_pfns);
>-    rec.length += nr_pages * PAGE_SIZE;
>+    rec.length += nr_pages_to_send * PAGE_SIZE;
> 
>     for ( i = 0; i < nr_pfns; ++i )
>  rec_pfns[i] = ((uint64_t)(types[i]) << 32) | ctx->save.batch_pfns[i];
>@@ -235,7 +237,7 @@ static int write_batch(struct xc_sr_context *ctx)
> 
>     iovcnt = 4;
> 
>-    if ( nr_pages )
>+    if ( nr_pages_to_send )
>     {
>         for ( i = 0; i < nr_pfns; ++i )
>         {
>@@ -244,7 +246,7 @@ static int write_batch(struct xc_sr_context *ctx)
>                 iov[iovcnt].iov_base = guest_data[i];
>                 iov[iovcnt].iov_len = PAGE_SIZE;
>                 iovcnt++;
>-                --nr_pages;
>+                --nr_pages_to_send;
>             }
>         }
>     }
>@@ -256,7 +258,7 @@ static int write_batch(struct xc_sr_context *ctx)
>     }
> 
>     /* Sanity check we have sent all the pages we expected to. */
>-    assert(nr_pages == 0);
>+    assert(nr_pages_to_send == 0);
>     rc = ctx->save.nr_batch_pfns = 0;
> 
>  err:



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