linux-kernel - [PATCH] mm/dev_pfn: Exclude MEMORY_DEVICE_PRIVATE while computing virtual address

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Message-Id: <1558089514-25067-1-git-send-email-anshuman.khandual@arm.com>
Date:   Fri, 17 May 2019 16:08:34 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        jglisse@...hat.com, ldufour@...ux.vnet.ibm.com
Subject: [PATCH] mm/dev_pfn: Exclude MEMORY_DEVICE_PRIVATE while computing virtual address

The presence of struct page does not guarantee linear mapping for the pfn
physical range. Device private memory which is non-coherent is excluded
from linear mapping during devm_memremap_pages() though they will still
have struct page coverage. Just check for device private memory before
giving out virtual address for a given pfn.

Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
All these helper functions are all pfn_t related but could not figure out
another way of determining a private pfn without looking into it's struct
page. pfn_t_to_virt() is not getting used any where in mainline kernel.Is
it used by out of tree drivers ? Should we then drop it completely ?

 include/linux/pfn_t.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
index 7bb7785..3c202a1 100644
--- a/include/linux/pfn_t.h
+++ b/include/linux/pfn_t.h
@@ -68,7 +68,7 @@ static inline phys_addr_t pfn_t_to_phys(pfn_t pfn)
 
 static inline void *pfn_t_to_virt(pfn_t pfn)
 {
-	if (pfn_t_has_page(pfn))
+	if (pfn_t_has_page(pfn) && !is_device_private_page(pfn_t_to_page(pfn)))
 		return __va(pfn_t_to_phys(pfn));
 	return NULL;
 }
-- 
2.7.4