On 12/13/21 6:27 AM, Baoquan He wrote:

In some places of the current kernel, it assumes that dma zone must have managed pages if CONFIG_ZONE_DMA is enabled. While this is not always true. E.g in kdump kernel of x86_64, only low 1M is presented and locked down at very early stage of boot, so that there's no managed pages at all in DMA zone. This exception will always cause page allocation failure if page is requested from DMA zone.

Here add function has_managed_dma() and the relevant helper functions to check if there's DMA zone with managed pages. It will be used in later patches.

Fixes: 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified") Cc: stable@vger.kernel.org Signed-off-by: Baoquan He bhe@redhat.com

Acked-by: John Donnelly john.p.donnelly@oracle.com Tested-by: John Donnelly john.p.donnelly@oracle.com

---

v2->v3: Rewrite has_managed_dma() in a simpler and more efficient way which is sugggested by DavidH.

include/linux/mmzone.h | 9 +++++++++ mm/page_alloc.c | 15 +++++++++++++++ 2 files changed, 24 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 58e744b78c2c..6e1b726e9adf 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1046,6 +1046,15 @@ static inline int is_highmem_idx(enum zone_type idx) #endif } +#ifdef CONFIG_ZONE_DMA +bool has_managed_dma(void); +#else +static inline bool has_managed_dma(void) +{

• return false;

+} +#endif

• /**
  • is_highmem - helper function to quickly check if a struct zone is a

  •          highmem zone or not.  This is an attempt to keep references
    

diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c5952749ad40..7c7a0b5de2ff 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -9460,3 +9460,18 @@ bool take_page_off_buddy(struct page *page) return ret; } #endif

+#ifdef CONFIG_ZONE_DMA +bool has_managed_dma(void) +{

• struct pglist_data *pgdat;
• for_each_online_pgdat(pgdat) {

• struct zone *zone = &pgdat->node_zones[ZONE_DMA];
  

• if (managed_zone(zone))
  

• 	return true;
  

• }
• return false;

+} +#endif /* CONFIG_ZONE_DMA */