Subject: [RFC PATCH v2 03/21] mm: Allow DMA mapping of pages which are not online

From: Jonathan Lemon <[email-masked]>
Date: Mon, 27 Jul 2020 15:44:26 -0700

Change the system RAM check from 'valid' to 'online', so dummy
pages which refer to external DMA resources can be mapped.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 include/linux/dma-mapping.h | 4 ++--
 include/linux/mmzone.h      | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index a33ed3954ed4..e9b1a8431568 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -348,8 +348,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
 
 	BUG_ON(!valid_dma_direction(dir));
 
-	/* Don't allow RAM to be mapped */
-	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
+	/* Don't allow online RAM to be mapped */
+	if (WARN_ON_ONCE(pfn_online(PHYS_PFN(phys_addr))))
 		return DMA_MAPPING_ERROR;
 
 	if (dma_is_direct(ops))
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index f6f884970511..d0c6fc553304 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1348,6 +1348,13 @@ static inline unsigned long next_present_section_nr(unsigned long section_nr)
 	return -1;
 }
 
+static inline int pfn_online(unsigned long pfn)
+{
+	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+		return 0;
+	return online_section(__nr_to_section(pfn_to_section_nr(pfn)));
+}
+
 /*
  * These are _only_ used during initialisation, therefore they
  * can use __initdata ...  They could have names to indicate
-- 
2.24.1