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Patch "mm: fix cache mode of dax pmd mappings" has been added to the 4.7-stable tree

PATCH [email protected] 1 participant 1 message Sep 22, 2016

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This is a note to let you know that I've just added the patch titled

mm: fix cache mode of dax pmd mappings

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-fix-cache-mode-of-dax-pmd-mappings.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 9049771f7d5490a302589976984810064c83ab40 Mon Sep 17 00:00:00 2001

From: Dan Williams <[email protected]>
Date: Wed, 7 Sep 2016 08:51:21 -0700
Subject: mm: fix cache mode of dax pmd mappings

From: Dan Williams <[email protected]>

commit 9049771f7d5490a302589976984810064c83ab40 upstream.

track_pfn_insert() in vmf_insert_pfn_pmd() is marking dax mappings as uncacheable rendering them impractical for application usage. DAX-pte mappings are cached and the goal of establishing DAX-pmd mappings is to attain more performance, not dramatically less (3 orders of magnitude).

track_pfn_insert() relies on a previous call to reserve_memtype() to establish the expected page_cache_mode for the range. While memremap() arranges for reserve_memtype() to be called, devm_memremap_pages() does not. So, teach track_pfn_insert() and untrack_pfn() how to handle tracking without a vma, and arrange for devm_memremap_pages() to establish the write-back-cache reservation in the memtype tree.

Cc Matthew Wilcox <[email protected]>
Cc Ross Zwisler <[email protected]>
Cc Nilesh Choudhury <[email protected]>
Cc Kirill A. Shutemov <[email protected]>
Reported-by Toshi Kani <[email protected]>
Reported-by Kai Zhang <[email protected]>
Acked-by Andrew Morton <[email protected]>
Signed-off-by Dan Williams <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/mm/pat.c |   17 ++++++++++-------
 kernel/memremap.c |    9 +++++++++
 2 files changed, 19 insertions(+), 7 deletions(-)
arch/x86/mm/pat.c +10 -7
@@ -931,9 +931,10 @@ int track_pfn_copy(struct vm_area_struct
 }
 
 /*
- * prot is passed in as a parameter for the new mapping. If the vma has a
- * linear pfn mapping for the entire range reserve the entire vma range with
- * single reserve_pfn_range call.
+ * prot is passed in as a parameter for the new mapping. If the vma has
+ * a linear pfn mapping for the entire range, or no vma is provided,
+ * reserve the entire pfn + size range with single reserve_pfn_range
+ * call.
  */
 int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
 		    unsigned long pfn, unsigned long addr, unsigned long size)

@@ -942,11 +943,12 @@ int track_pfn_remap(struct vm_area_struc
 	enum page_cache_mode pcm;
 
 	/* reserve the whole chunk starting from paddr */
-	if (addr == vma->vm_start && size == (vma->vm_end - vma->vm_start)) {
+	if (!vma || (addr == vma->vm_start
+				&& size == (vma->vm_end - vma->vm_start))) {
 		int ret;
 
 		ret = reserve_pfn_range(paddr, size, prot, 0);
-		if (!ret)
+		if (ret == 0 && vma)
 			vma->vm_flags |= VM_PAT;
 		return ret;
 	}

@@ -1001,7 +1003,7 @@ void untrack_pfn(struct vm_area_struct *
 	resource_size_t paddr;
 	unsigned long prot;
 
-	if (!(vma->vm_flags & VM_PAT))
+	if (vma && !(vma->vm_flags & VM_PAT))
 		return;
 
 	/* free the chunk starting from pfn or the whole chunk */

@@ -1015,7 +1017,8 @@ void untrack_pfn(struct vm_area_struct *
 		size = vma->vm_end - vma->vm_start;
 	}
 	free_pfn_range(paddr, size);
-	vma->vm_flags &= ~VM_PAT;
+	if (vma)
+		vma->vm_flags &= ~VM_PAT;
 }
 
 /*
kernel/memremap.c +9 -0
@@ -253,6 +253,7 @@ static void devm_memremap_pages_release(
 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(resource_size(res), SECTION_SIZE);
 	arch_remove_memory(align_start, align_size);
+	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
 	pgmap_radix_release(res);
 	dev_WARN_ONCE(dev, pgmap->altmap && pgmap->altmap->alloc,
 			"%s: failed to free all reserved pages\n", __func__);

@@ -288,6 +289,7 @@ void *devm_memremap_pages(struct device
 		struct percpu_ref *ref, struct vmem_altmap *altmap)
 {
 	resource_size_t key, align_start, align_size, align_end;
+	pgprot_t pgprot = PAGE_KERNEL;
 	struct dev_pagemap *pgmap;
 	struct page_map *page_map;
 	int error, nid, is_ram;

@@ -363,6 +365,11 @@ void *devm_memremap_pages(struct device
 	if (nid < 0)
 		nid = numa_mem_id();
 
+	error = track_pfn_remap(NULL, &pgprot, PHYS_PFN(align_start), 0,
+			align_size);
+	if (error)
+		goto err_pfn_remap;
+
 	error = arch_add_memory(nid, align_start, align_size, true);
 	if (error)
 		goto err_add_memory;

@@ -383,6 +390,8 @@ void *devm_memremap_pages(struct device
 	return __va(res->start);
 
  err_add_memory:
+	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
+ err_pfn_remap:
  err_radix:
 	pgmap_radix_release(res);
 	devres_free(page_map);

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/mm-fix-cache-mode-of-dax-pmd-mappings.patch