x86/paging: deal with log-dirty stats overflow

While the precise values are unlikely of interest once they exceed 4
billion (allowing us to leave alone the domctl struct), we still
shouldn't wrap or truncate the actual values. It is in particular
problematic if the truncated values were zero (causing libxenguest to
skip an iteration altogether) or a very small value (leading to
premature exiting of the pre-copy phase).

Change the internal fields to unsigned long, and suitably saturate for
copying to guest context.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index c304c24526006f5440a4a092145a05ba173cec1d..dd6b2bdf6fd6b63f2c67f1fc60e3a8430bf1a377 100644 (file)
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -446,14 +446,16 @@ static int paging_log_dirty_op(struct domain *d,
 
     clean = (sc->op == XEN_DOMCTL_SHADOW_OP_CLEAN);
 
-    PAGING_DEBUG(LOGDIRTY, "log-dirty %s: dom %u faults=%u dirty=%u\n",
+    PAGING_DEBUG(LOGDIRTY, "log-dirty %s: dom %u faults=%lu dirty=%lu\n",
                  (clean) ? "clean" : "peek",
                  d->domain_id,
                  d->arch.paging.log_dirty.fault_count,
                  d->arch.paging.log_dirty.dirty_count);
 
-    sc->stats.fault_count = d->arch.paging.log_dirty.fault_count;
-    sc->stats.dirty_count = d->arch.paging.log_dirty.dirty_count;
+    sc->stats.fault_count = min(d->arch.paging.log_dirty.fault_count,
+                                UINT32_MAX + 0UL);
+    sc->stats.dirty_count = min(d->arch.paging.log_dirty.dirty_count,
+                                UINT32_MAX + 0UL);
 
     if ( guest_handle_is_null(sc->dirty_bitmap) )
         /* caller may have wanted just to clean the state or access stats. */

diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 7213d184b0162ea6c07c5eaded22cf1c0e08a5a5..92d54de0b9a1218e729fe4a843904c6a52a4bdd3 100644 (file)
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -190,8 +190,8 @@ struct log_dirty_domain {
     unsigned int   failed_allocs;
 
     /* log-dirty mode stats */
-    unsigned int   fault_count;
-    unsigned int   dirty_count;
+    unsigned long  fault_count;
+    unsigned long  dirty_count;
 
     /* functions which are paging mode specific */
     const struct log_dirty_ops {