linux-kernel - Re: [PATCH 5/7] mm/gup: Implement dev_pagemap logic in generic get_user_pages

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Date:   Fri, 17 Mar 2017 20:27:12 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Steve Capper <steve.capper@...aro.org>,
        Dann Frazier <dann.frazier@...onical.com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 5/7] mm/gup: Implement dev_pagemap logic in generic
 get_user_pages_fast()

On Thu, Mar 16, 2017 at 06:26:53PM +0300, Kirill A. Shutemov wrote:
> +static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
> +		unsigned long end, struct page **pages, int *nr)
> +{
> +	unsigned long fault_pfn;
> +
> +	fault_pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> +	return __gup_device_huge(fault_pfn, addr, end, pages, nr);
> +}
> +
> +static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
> +		unsigned long end, struct page **pages, int *nr)
> +{
> +	unsigned long fault_pfn;
> +
> +	fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> +	return __gup_device_huge(fault_pfn, addr, end, pages, nr);
> +}
> +

PowerPC doesn't [always] provide pmd_pfn() and pud_pfn().

Fixup:

diff --git a/mm/gup.c b/mm/gup.c
index 5cc489d98562..6f36cbc294cf 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1287,6 +1287,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 }
 #endif /* __HAVE_ARCH_PTE_SPECIAL */
 
+#ifdef __HAVE_ARCH_PTE_DEVMAP
 static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 		unsigned long end, struct page **pages, int *nr)
 {
@@ -1328,6 +1329,21 @@ static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
 	fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 	return __gup_device_huge(fault_pfn, addr, end, pages, nr);
 }
+#else
+static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
+		unsigned long end, struct page **pages, int *nr)
+{
+	BUILD_BUG();
+	return 0;
+}
+
+static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
+		unsigned long end, struct page **pages, int *nr)
+{
+	BUILD_BUG();
+	return 0;
+}
+#endif
 
 static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		unsigned long end, int write, struct page **pages, int *nr)
@@ -1338,7 +1354,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (!pmd_access_permitted(orig, write))
 		return 0;
 
-	VM_BUG_ON(!pfn_valid(pmd_pfn(orig)));
 	if (pmd_devmap(orig))
 		return __gup_device_huge_pmd(orig, addr, end, pages, nr);
 
@@ -1378,7 +1393,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 	if (!pud_access_permitted(orig, write))
 		return 0;
 
-	VM_BUG_ON(!pfn_valid(pud_pfn(orig)));
 	if (pud_devmap(orig))
 		return __gup_device_huge_pud(orig, addr, end, pages, nr);
 
-- 
 Kirill A. Shutemov