domain_validate: Account for NVDIMM label size properly when checking for memory conflicts

As of v9.8.0-rc1~7 we check whether two <memory/> devices don't
overlap (since we allow setting where a <memory/> device should
be mapped to). We do this pretty straightforward, by comparing
start and end address of each <memory/> device combination.
But since only the start address is given (an exposed in the
XML), the end address is computed trivially as:

  start + mem->size * 1024

And for majority of memory device types this works. Except for
NVDIMMs. For them the <memory/> device consists of two separate
regions: 1) actual memory device, and 2) label.

Label is where NVDIMM stores some additional information like
namespaces partition and so on. But it's not mapped into the
guest the same way as actual memory device. In fact, mem->size is
a sum of both actual memory device and label sizes. And to make
things a bit worse, both sizes are subject to alignment (either
the alignsize value specified in XML, or system page size if not
specified in XML).

Therefore, to get the size of actual memory device we need to
take mem->size and substract label size rounded up to alignment.

If we don't do this we report there's an overlap between two
NVDIMMs even when in reality there's none.

Fixes: 3fd64fb0e2
Fixes: 91f9a9fb4f
Resolves: https://issues.redhat.com/browse/RHEL-4452?focusedId=23805174#comment-23805174
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

src/conf/domain_validate.c

@@ -2225,6 +2225,53 @@ virDomainHostdevDefValidate(const virDomainHostdevDef *hostdev)
 }
 
 
+/**
+ * virDomainMemoryGetMappedSize:
+ * @mem: memory device definition
+ *
+ * For given memory device definition (@mem) calculate size mapped into
+ * the guest. This is usually mem->size, except for NVDIMM where its
+ * label is mapped elsewhere.
+ *
+ * Returns: Number of bytes a memory device takes when mapped into a
+ * guest.
+ */
+static unsigned long long
+virDomainMemoryGetMappedSize(const virDomainMemoryDef *mem)
+{
+    unsigned long long ret = mem->size;
+
+    if (mem->model == VIR_DOMAIN_MEMORY_MODEL_NVDIMM) {
+        unsigned long long alignsize = mem->source.nvdimm.alignsize;
+        unsigned long long labelsize = 0;
+
+        /* For NVDIMM the situation is a bit more complicated. Firstly,
+         * its <label/> is not mapped as a part of memory device, so we
+         * must subtract label size from NVDIMM size. Secondly,
+         * remaining memory is then aligned again (rounded down). But
+         * for our purposes we might just round label size up and
+         * achieve the same (numeric) result. */
+
+        if (alignsize == 0) {
+            long pagesize = virGetSystemPageSizeKB();
+
+            /* If no alignment is specified in the XML, fallback to
+             * system page size alignment. */
+            if (pagesize > 0)
+                alignsize = pagesize;
+        }
+
+        if (alignsize > 0) {
+            labelsize = VIR_ROUND_UP(mem->target.nvdimm.labelsize, alignsize);
+
+            ret -= labelsize;
+        }
+    }
+
+    return ret * 1024;
+}
+
+
 static int
 virDomainMemoryDefCheckConflict(const virDomainMemoryDef *mem,
                                 const virDomainDef *def)
@@ -2259,7 +2306,7 @@ virDomainMemoryDefCheckConflict(const virDomainMemoryDef *mem,
     }
 
     /* thisStart and thisEnd are in bytes, mem->size in kibibytes */
-    thisEnd = thisStart + mem->size * 1024;
+    thisEnd = thisStart + virDomainMemoryGetMappedSize(mem);
 
     for (i = 0; i < def->nmems; i++) {
         const virDomainMemoryDef *other = def->mems[i];
@@ -2316,7 +2363,7 @@ virDomainMemoryDefCheckConflict(const virDomainMemoryDef *mem,
         if (thisStart == 0 || otherStart == 0)
             continue;
 
-        otherEnd = otherStart + other->size * 1024;
+        otherEnd = otherStart + virDomainMemoryGetMappedSize(other);
 
         if ((thisStart <= otherStart && thisEnd > otherStart) ||
             (otherStart <= thisStart && otherEnd > thisStart)) {