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

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

[Lorenzo Stoakes]

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@oracle.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

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

[kernel test robot]

Hi Lorenzo,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on v6.13-rc1 next-20241128]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Lorenzo-Stoakes/intel_th-avoid-using-deprecated-page-mapping-index-fields/20241202-202330
base:   linus/master
patch link:    https://lore.kernel.org/r/20241202122127.51313-1-lorenzo.stoakes%40oracle.com
patch subject: [PATCH] intel_th: avoid using deprecated page->mapping, index fields
config: arm-randconfig-004-20241202 (https://download.01.org/0day-ci/archive/20241203/202412030410.qX3ejEnD-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project 592c0fe55f6d9a811028b5f3507be91458ab2713)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241203/202412030410.qX3ejEnD-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202412030410.qX3ejEnD-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "vmf_insert_mixed" [drivers/hwtracing/intel_th/intel_th_msu.ko] undefined!

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[Lorenzo Stoakes]

On Tue, Dec 03, 2024 at 04:34:33AM +0800, kernel test robot wrote:
> Hi Lorenzo,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on linus/master]
> [also build test ERROR on v6.13-rc1 next-20241128]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Lorenzo-Stoakes/intel_th-avoid-using-deprecated-page-mapping-index-fields/20241202-202330
> base:   linus/master
> patch link:    https://lore.kernel.org/r/20241202122127.51313-1-lorenzo.stoakes%40oracle.com
> patch subject: [PATCH] intel_th: avoid using deprecated page->mapping, index fields
> config: arm-randconfig-004-20241202 (https://download.01.org/0day-ci/archive/20241203/202412030410.qX3ejEnD-lkp@intel.com/config)
> compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project 592c0fe55f6d9a811028b5f3507be91458ab2713)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241203/202412030410.qX3ejEnD-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202412030410.qX3ejEnD-lkp@intel.com/
>
> All errors (new ones prefixed by >>, old ones prefixed by <<):
>
> >> ERROR: modpost: "vmf_insert_mixed" [drivers/hwtracing/intel_th/intel_th_msu.ko] undefined!

This is a nommu arch, while the info above doesn't tell you this, the fact it
says this function, defined in mm/memory.c, is not availble, indicates that this
is the only possible cause.

And, as this is a driver that literally depends on page faulting to work at all,
the proper solution is to adjust the Kconfig to depend on CONFIG_MMU. I'll send
a v2.

>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki