linux-kernel - [PATCH RFC 02/10] mm: Handle pmd entries in follow

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Date:   Fri, 10 Jan 2020 19:03:05 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     linux-nvdimm@...ts.01.org
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Liran Alon <liran.alon@...cle.com>,
        Nikita Leshenko <nikita.leshchenko@...cle.com>,
        Barret Rhoden <brho@...gle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [PATCH RFC 02/10] mm: Handle pmd entries in follow_pfn()

When follow_pfn hits a pmd_huge() it won't return a valid PFN
given it's usage of follow_pte(). Fix that up to pass a @pmdpp
and thus allow callers to get the pmd pointer. If we encounter
such a huge page, we calculate the pfn offset to the PMD
accordingly.

This allows KVM to handle 2M hugepage pfns on VM_PFNMAP vmas.

Signed-off-by: Joao Martins <joao.m.martins@...cle.com>
---
 mm/memory.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index cfc3668bddeb..db99684d2cb3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4366,6 +4366,7 @@ EXPORT_SYMBOL(follow_pte_pmd);
 int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 	unsigned long *pfn)
 {
+	pmd_t *pmdpp = NULL;
 	int ret = -EINVAL;
 	spinlock_t *ptl;
 	pte_t *ptep;
@@ -4373,10 +4374,14 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address,
 	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, &pmdpp, &ptl);
 	if (ret)
 		return ret;
-	*pfn = pte_pfn(*ptep);
+	if (pmdpp)
+		*pfn = pmd_pfn(*pmdpp) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+	else
+		*pfn = pte_pfn(*ptep);
 	pte_unmap_unlock(ptep, ptl);
 	return 0;
 }
-- 
2.17.1