Commit 4c89792e authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm: rename vm_ops->find_special_page() to vm_ops->find_normal_page() 

...  and hide it behind a kconfig option.  There is really no need for any
!xen code to perform this check.

The naming is a bit off: we want to find the "normal" page when a PTE was
marked "special".  So it's really not "finding a special" page.

Improve the documentation, and add a comment in the code where XEN ends up
performing the pte_mkspecial() through a hypercall.  More details can be
found in commit 923b2919 ("xen/gntdev: mark userspace PTEs as special
on x86 PV guests").

Link: https://lkml.kernel.org/r/20250811112631.759341-12-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarWei Yang <richard.weiyang@gmail.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 2db30816

drivers/xen/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -138,6 +138,7 @@ config XEN_GNTDEV 
	depends on XEN

	default m

	select MMU_NOTIFIER

	select FIND_NORMAL_PAGE

	help

	  Allows userspace processes to use grants.

drivers/xen/gntdev.c

+3 −2
Original line number Diff line number Diff line
@@ -321,6 +321,7 @@ static int find_grant_ptes(pte_t *pte, unsigned long addr, void *data) 
	BUG_ON(pgnr >= map->count);

	pte_maddr = arbitrary_virt_to_machine(pte).maddr;



	/* Note: this will perform a pte_mkspecial() through the hypercall. */

	gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,

			  map->grants[pgnr].ref,

			  map->grants[pgnr].domid);
@@ -528,7 +529,7 @@ static void gntdev_vma_close(struct vm_area_struct *vma) 
	gntdev_put_map(priv, map);

}



static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma,

static struct page *gntdev_vma_find_normal_page(struct vm_area_struct *vma,

						 unsigned long addr)

{

	struct gntdev_grant_map *map = vma->vm_private_data;
@@ -539,7 +540,7 @@ static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma, 
static const struct vm_operations_struct gntdev_vmops = {

	.open = gntdev_vma_open,

	.close = gntdev_vma_close,

	.find_special_page = gntdev_vma_find_special_page,

	.find_normal_page = gntdev_vma_find_normal_page,

};



/* ------------------------------------------------------------------ */

include/linux/mm.h

+13 −5
Original line number Diff line number Diff line
@@ -657,13 +657,21 @@ struct vm_operations_struct { 
	struct mempolicy *(*get_policy)(struct vm_area_struct *vma,

					unsigned long addr, pgoff_t *ilx);

#endif

#ifdef CONFIG_FIND_NORMAL_PAGE

	/*

	 * Called by vm_normal_page() for special PTEs to find the

	 * page for @addr.  This is useful if the default behavior

	 * (using pte_page()) would not find the correct page.

	 * Called by vm_normal_page() for special PTEs in @vma at @addr. This

	 * allows for returning a "normal" page from vm_normal_page() even

	 * though the PTE indicates that the "struct page" either does not exist

	 * or should not be touched: "special".

	 *

	 * Do not add new users: this really only works when a "normal" page

	 * was mapped, but then the PTE got changed to something weird (+

	 * marked special) that would not make pte_pfn() identify the originally

	 * inserted page.

	 */

	struct page *(*find_special_page)(struct vm_area_struct *vma,

	struct page *(*find_normal_page)(struct vm_area_struct *vma,

					 unsigned long addr);

#endif /* CONFIG_FIND_NORMAL_PAGE */

};



#ifdef CONFIG_NUMA_BALANCING

mm/Kconfig

+2 −0
Original line number Diff line number Diff line
@@ -1381,6 +1381,8 @@ config PT_RECLAIM 


	  Note: now only empty user PTE page table pages will be reclaimed.



config FIND_NORMAL_PAGE

	def_bool n



source "mm/damon/Kconfig"

mm/memory.c

+10 −2
Original line number Diff line number Diff line
@@ -639,6 +639,12 @@ static void print_bad_page_map(struct vm_area_struct *vma, 
 * trivial. Secondly, an architecture may not have a spare page table

 * entry bit, which requires a more complicated scheme, described below.

 *

 * With CONFIG_FIND_NORMAL_PAGE, we might have the "special" bit set on

 * page table entries that actually map "normal" pages: however, that page

 * cannot be looked up through the PFN stored in the page table entry, but

 * instead will be looked up through vm_ops->find_normal_page(). So far, this

 * only applies to PTEs.

 *

 * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a

 * special mapping (even if there are underlying and valid "struct pages").

 * COWed pages of a VM_PFNMAP are always normal.
@@ -679,8 +685,10 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma, 
{

	if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {

		if (unlikely(special)) {

			if (vma->vm_ops && vma->vm_ops->find_special_page)

				return vma->vm_ops->find_special_page(vma, addr);

#ifdef CONFIG_FIND_NORMAL_PAGE

			if (vma->vm_ops && vma->vm_ops->find_normal_page)

				return vma->vm_ops->find_normal_page(vma, addr);

#endif /* CONFIG_FIND_NORMAL_PAGE */

			if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))

				return NULL;

			if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))