linux-kernel - [PATCH 3.16 100/131] mm: Add vm_insert_pfn

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Message-ID: <lsq.1538257387.154488040@decadent.org.uk>
Date:   Sat, 29 Sep 2018 22:43:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Quentin Casasnovas" <quentin.casasnovas@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Fenghua Yu" <fenghua.yu@...el.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Oleg Nesterov" <oleg@...hat.com>,
        "Andy Lutomirski" <luto@...capital.net>,
        "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Kees Cook" <keescook@...omium.org>
Subject: [PATCH 3.16 100/131] mm: Add vm_insert_pfn_prot()

3.16.59-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@...nel.org>

commit 1745cbc5d0dee0749a6bc0ea8e872c5db0074061 upstream.

The x86 vvar vma contains pages with differing cacheability
flags.  x86 currently implements this by manually inserting all
the ptes using (io_)remap_pfn_range when the vma is set up.

x86 wants to move to using .fault with VM_FAULT_NOPAGE to set up
the mappings as needed.  The correct API to use to insert a pfn
in .fault is vm_insert_pfn(), but vm_insert_pfn() can't override the
vma's cache mode, and the HPET page in particular needs to be
uncached despite the fact that the rest of the VMA is cached.

Add vm_insert_pfn_prot() to support varying cacheability within
the same non-COW VMA in a more sane manner.

x86 could alternatively use multiple VMAs, but that's messy,
would break CRIU, and would create unnecessary VMAs that would
waste memory.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Acked-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/d2938d1eb37be7a5e4f86182db646551f11e45aa.1451446564.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 25 +++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1965,6 +1965,8 @@ int remap_pfn_range(struct vm_area_struc
 int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
 int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 			unsigned long pfn);
+int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, pgprot_t pgprot);
 int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
 			unsigned long pfn);
 int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1574,8 +1574,29 @@ out:
 int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 			unsigned long pfn)
 {
+	return vm_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_pfn);
+
+/**
+ * vm_insert_pfn_prot - insert single pfn into user vma with specified pgprot
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ * @pgprot: pgprot flags for the inserted page
+ *
+ * This is exactly like vm_insert_pfn, except that it allows drivers to
+ * to override pgprot on a per-page basis.
+ *
+ * This only makes sense for IO mappings, and it makes no sense for
+ * cow mappings.  In general, using multiple vmas is preferable;
+ * vm_insert_pfn_prot should only be used if using multiple VMAs is
+ * impractical.
+ */
+int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, pgprot_t pgprot)
+{
 	int ret;
-	pgprot_t pgprot = vma->vm_page_prot;
 	/*
 	 * Technically, architectures with pte_special can avoid all these
 	 * restrictions (same for remap_pfn_range).  However we would like
@@ -1597,7 +1618,7 @@ int vm_insert_pfn(struct vm_area_struct
 
 	return ret;
 }
-EXPORT_SYMBOL(vm_insert_pfn);
+EXPORT_SYMBOL(vm_insert_pfn_prot);
 
 int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
 			unsigned long pfn)