linux-kernel - [RFC V2 21/37] mm: support dmem huge pmd for follow

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Message-Id: <c83a4e698999902057cdf8e3a662ec6837f6f466.1607332046.git.yuleixzhang@tencent.com>
Date:   Mon,  7 Dec 2020 19:31:14 +0800
From:   yulei.kernel@...il.com
To:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, naoya.horiguchi@....com,
        viro@...iv.linux.org.uk, pbonzini@...hat.com
Cc:     joao.m.martins@...cle.com, rdunlap@...radead.org,
        sean.j.christopherson@...el.com, xiaoguangrong.eric@...il.com,
        kernellwp@...il.com, lihaiwei.kernel@...il.com,
        Yulei Zhang <yuleixzhang@...cent.com>,
        Chen Zhuo <sagazchen@...cent.com>
Subject: [RFC V2 21/37] mm: support dmem huge pmd for follow_pfn()

From: Yulei Zhang <yuleixzhang@...cent.com>

follow_pfn() will get pfn of pmd if huge pmd is encountered.

Signed-off-by: Chen Zhuo <sagazchen@...cent.com>
Signed-off-by: Yulei Zhang <yuleixzhang@...cent.com>
---
 mm/memory.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 6b60981..abb9148 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4807,15 +4807,23 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 	int ret = -EINVAL;
 	spinlock_t *ptl;
 	pte_t *ptep;
+	pmd_t *pmdp = NULL;
 
 	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
 		return ret;
 
-	ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
+	ret = follow_pte_pmd(vma->vm_mm, address, NULL, &ptep, &pmdp, &ptl);
 	if (ret)
 		return ret;
-	*pfn = pte_pfn(*ptep);
-	pte_unmap_unlock(ptep, ptl);
+
+	if (pmdp) {
+		*pfn = pmd_pfn(*pmdp) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+		spin_unlock(ptl);
+	} else {
+		*pfn = pte_pfn(*ptep);
+		pte_unmap_unlock(ptep, ptl);
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL(follow_pfn);
-- 
1.8.3.1