linux-kernel - [PATCH 2/7] xen/gntdev,x86: Remove apply_to_page

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Date:   Mon, 12 Apr 2021 10:00:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, x86@...nel.org,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, chris@...is-wilson.co.uk,
        intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
        keescook@...omium.org, hch@....de
Subject: [PATCH 2/7] xen/gntdev,x86: Remove apply_to_page_range() use from module

Instead of relying on apply_to_page_range() being available to
modules, move its use into core kernel code and export it's
application.

NOTE: ideally we do: use_ptemod = !auto_translate_physmap &&
gnttab_map_avail_bits and remove this hack.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/xen/page.h |    2 ++
 arch/x86/xen/mmu.c              |   26 ++++++++++++++++++++++++++
 drivers/xen/gntdev.c            |   23 +----------------------
 3 files changed, 29 insertions(+), 22 deletions(-)

--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -370,4 +370,6 @@ static inline unsigned long xen_get_swio
 	return __get_free_pages(__GFP_NOWARN, order);
 }
 
+extern void xen_set_grant_as_special(struct vm_area_struct *vma);
+
 #endif /* _ASM_X86_XEN_PAGE_H */
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -51,3 +51,29 @@ int xen_unmap_domain_gfn_range(struct vm
 	return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(xen_unmap_domain_gfn_range);
+
+static int set_grant_ptes_as_special(pte_t *pte, unsigned long addr, void *data)
+{
+	set_pte_at(current->mm, addr, pte, pte_mkspecial(*pte));
+	return 0;
+}
+
+void xen_set_grant_as_special(struct vm_area_struct *vma)
+{
+	if (xen_feature(XENFEAT_gnttab_map_avail_bits))
+		return;
+
+	/*
+	 * If the PTEs were not made special by the grant map
+	 * hypercall, do so here.
+	 *
+	 * This is racy since the mapping is already visible
+	 * to userspace but userspace should be well-behaved
+	 * enough to not touch it until the mmap() call
+	 * returns.
+	 */
+	apply_to_page_range(vma->vm_mm, vma->vm_start,
+			    vma->vm_end - vma->vm_start,
+			    set_grant_ptes_as_special, NULL);
+}
+EXPORT_SYMBOL_GPL(xen_set_grant_as_special);
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -278,14 +278,6 @@ static int find_grant_ptes(pte_t *pte, u
 	return 0;
 }
 
-#ifdef CONFIG_X86
-static int set_grant_ptes_as_special(pte_t *pte, unsigned long addr, void *data)
-{
-	set_pte_at(current->mm, addr, pte, pte_mkspecial(*pte));
-	return 0;
-}
-#endif
-
 int gntdev_map_grant_pages(struct gntdev_grant_map *map)
 {
 	int i, err = 0;
@@ -1040,20 +1032,7 @@ static int gntdev_mmap(struct file *flip
 			goto out_put_map;
 	} else {
 #ifdef CONFIG_X86
-		/*
-		 * If the PTEs were not made special by the grant map
-		 * hypercall, do so here.
-		 *
-		 * This is racy since the mapping is already visible
-		 * to userspace but userspace should be well-behaved
-		 * enough to not touch it until the mmap() call
-		 * returns.
-		 */
-		if (!xen_feature(XENFEAT_gnttab_map_avail_bits)) {
-			apply_to_page_range(vma->vm_mm, vma->vm_start,
-					    vma->vm_end - vma->vm_start,
-					    set_grant_ptes_as_special, NULL);
-		}
+		xen_set_grant_as_special(vma);
 #endif
 	}