[RFC 5/6] Hibernate: Add check for pte_valid in saveable page

[Vivek Kumar]

Add check for pte_valid in saveable page after being checked for
the rest. This is required as PTE is removed for pages allocated
with dma_alloc_coherent with DMA_ATTR_NO_KERNEL_MAPPING flag set.
This patch makes sure that these pages are not considered for
snapshot.

Signed-off-by: Vivek Kumar <quic_vivekuma@xxxxxxxxxxx>
Signed-off-by: Prasanna Kumar <quic_kprasan@xxxxxxxxxxx>
---
 kernel/power/snapshot.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 2a40675..a6ad2a5 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1308,6 +1308,41 @@ static inline void *saveable_highmem_page(struct zone *z, unsigned long p)
 }
 #endif /* CONFIG_HIGHMEM */
 
+static bool kernel_pte_present(struct page *page)
+{
+	pgd_t *pgdp;
+	p4d_t *p4dp;
+	pud_t *pudp, pud;
+	pmd_t *pmdp, pmd;
+	pte_t *ptep;
+	unsigned long addr = (unsigned long)page_address(page);
+
+	pgdp = pgd_offset_k(addr);
+	if (pgd_none(READ_ONCE(*pgdp)))
+		return false;
+
+	p4dp = p4d_offset(pgdp, addr);
+	if (p4d_none(READ_ONCE(*p4dp)))
+		return false;
+
+	pudp = pud_offset(p4dp, addr);
+	pud = READ_ONCE(*pudp);
+	if (pud_none(pud))
+		return false;
+	if (pud_sect(pud))
+		return true;
+
+	pmdp = pmd_offset(pudp, addr);
+	pmd = READ_ONCE(*pmdp);
+	if (pmd_none(pmd))
+		return false;
+	if (pmd_sect(pmd))
+		return true;
+
+	ptep = pte_offset_kernel(pmdp, addr);
+	return pte_valid(READ_ONCE(*ptep));
+}
+
 /**
  * saveable_page - Check if the given page is saveable.
  *
@@ -1341,6 +1376,14 @@ static struct page *saveable_page(struct zone *zone, unsigned long pfn)
 	    && (!kernel_page_present(page) || pfn_is_nosave(pfn)))
 		return NULL;
 
+	/*
+	 * Even if page is not reserved and if it's not present in kernel PTE;
+	 * don't snapshot it ! This happens to the pages allocated using
+	 * __dma_alloc_coherent with DMA_ATTR_NO_KERNEL_MAPPING flag set.
+	 */
+	if (!kernel_pte_present(page))
+		return NULL;
+
 	if (page_is_guard(page))
 		return NULL;
 
-- 
2.7.4