linux-kernel - [PATCH] intel_th: avoid using deprecated page->mapping, index fields

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Message-ID: <20241202122127.51313-1-lorenzo.stoakes@oracle.com>
Date: Mon,  2 Dec 2024 12:21:27 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH] intel_th: avoid using deprecated page->mapping, index fields

The struct page->mapping, index fields are deprecated and soon to be only
available as part of a folio.

It is likely the intel_th code which sets page->mapping, index is was
implemented out of concern that some aspect of the page fault logic may
encounter unexpected problems should they not.

However, the appropriate interface for inserting kernel-allocated memory is
vm_insert_page() in a VM_MIXEDMAP. By using the helper function
vmf_insert_mixed() we can do this with minimal churn in the existing fault
handler.

By doing so, we bypass the remainder of the faulting logic. The pages are
still pinned so there is no possibility of anything unexpected being done
with the pages once established.

It would also be reasonable to pre-map everything on fault, however to
minimise churn we retain the fault handler.

We also eliminate all code which clears page->mapping on teardown as this
has now become unnecessary.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 drivers/hwtracing/intel_th/msu.c | 31 +++++++------------------------
 1 file changed, 7 insertions(+), 24 deletions(-)

diff --git a/drivers/hwtracing/intel_th/msu.c b/drivers/hwtracing/intel_th/msu.c
index 66123d684ac9..93b65a9731d7 100644
--- a/drivers/hwtracing/intel_th/msu.c
+++ b/drivers/hwtracing/intel_th/msu.c
@@ -19,6 +19,7 @@
 #include <linux/io.h>
 #include <linux/workqueue.h>
 #include <linux/dma-mapping.h>
+#include <linux/pfn_t.h>

 #ifdef CONFIG_X86
 #include <asm/set_memory.h>
@@ -967,7 +968,6 @@ static void msc_buffer_contig_free(struct msc *msc)
 	for (off = 0; off < msc->nr_pages << PAGE_SHIFT; off += PAGE_SIZE) {
 		struct page *page = virt_to_page(msc->base + off);

-		page->mapping = NULL;
 		__free_page(page);
 	}

@@ -1149,9 +1149,6 @@ static void __msc_buffer_win_free(struct msc *msc, struct msc_window *win)
 	int i;

 	for_each_sg(win->sgt->sgl, sg, win->nr_segs, i) {
-		struct page *page = msc_sg_page(sg);
-
-		page->mapping = NULL;
 		dma_free_coherent(msc_dev(win->msc)->parent->parent, PAGE_SIZE,
 				  sg_virt(sg), sg_dma_address(sg));
 	}
@@ -1592,22 +1589,10 @@ static void msc_mmap_close(struct vm_area_struct *vma)
 {
 	struct msc_iter *iter = vma->vm_file->private_data;
 	struct msc *msc = iter->msc;
-	unsigned long pg;

 	if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex))
 		return;

-	/* drop page _refcounts */
-	for (pg = 0; pg < msc->nr_pages; pg++) {
-		struct page *page = msc_buffer_get_page(msc, pg);
-
-		if (WARN_ON_ONCE(!page))
-			continue;
-
-		if (page->mapping)
-			page->mapping = NULL;
-	}
-
 	/* last mapping -- drop user_count */
 	atomic_dec(&msc->user_count);
 	mutex_unlock(&msc->buf_mutex);
@@ -1617,16 +1602,14 @@ static vm_fault_t msc_mmap_fault(struct vm_fault *vmf)
 {
 	struct msc_iter *iter = vmf->vma->vm_file->private_data;
 	struct msc *msc = iter->msc;
+	struct page *page;

-	vmf->page = msc_buffer_get_page(msc, vmf->pgoff);
-	if (!vmf->page)
+	page = msc_buffer_get_page(msc, vmf->pgoff);
+	if (!page)
 		return VM_FAULT_SIGBUS;

-	get_page(vmf->page);
-	vmf->page->mapping = vmf->vma->vm_file->f_mapping;
-	vmf->page->index = vmf->pgoff;
-
-	return 0;
+	get_page(page);
+	return vmf_insert_mixed(vmf->vma, vmf->address, page_to_pfn_t(page));
 }

 static const struct vm_operations_struct msc_mmap_ops = {
@@ -1667,7 +1650,7 @@ static int intel_th_msc_mmap(struct file *file, struct vm_area_struct *vma)
 		atomic_dec(&msc->user_count);

 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTCOPY);
+	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTCOPY | VM_MIXEDMAP);
 	vma->vm_ops = &msc_mmap_ops;
 	return ret;
 }
--
2.47.1