mm/page_alloc: fix MEMF_no_dma allocations for single NUMA

Currently dma_bitsize is zero by default on single NUMA node machines.
This makes all alloc_domheap_pages() calls with MEMF_no_dma return NULL.

There is only 1 user of MEMF_no_dma: dom0_memflags, which are used
during memory allocation for Dom0. Failing allocation with default
dom0_memflags is especially severe for the PV Dom0 case: it makes
alloc_chunk() to use suboptimal 2MB allocation algorithm with a search
for higher memory addresses.

This can lead to the NMI watchdog timeout during PV Dom0 construction
on some machines, which can be worked around by specifying "dma_bits"
in Xen's cmdline manually.

Fix the issue by ignoring MEMF_no_dma in cases when dma_bitsize is zero,
which means there is no DMA zone. This shouldn't cause any issues for
Dom0 because alloc_heap_pages() will first use higher memory addresses
for satisfying memory allocation requests.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 5ac2dddb173b69be259ce4b259e73f971a4816c1
master date: 2019-01-09 15:45:14 +0100

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 7d8c37ef36ecc89d4c9404f2b843d50af5c0f8f1..adede05509b64d768ede734067eeb4d63f1c7a44 100644 (file)
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1796,7 +1796,9 @@ struct page_info *alloc_domheap_pages(
     if ( memflags & MEMF_no_owner )
         memflags |= MEMF_no_refcount;
 
-    if ( dma_bitsize && ((dma_zone = bits_to_zone(dma_bitsize)) < zone_hi) )
+    if ( !dma_bitsize )
+        memflags &= ~MEMF_no_dma;
+    else if ( (dma_zone = bits_to_zone(dma_bitsize)) < zone_hi )
         pg = alloc_heap_pages(dma_zone + 1, zone_hi, order, memflags, d);
 
     if ( (pg == NULL) &&