[PATCH v1 09/11] s390/mm/fault: convert do_secure_storage_access() from follow_page() to folio_walk

David Hildenbrand
2024-08-02T15:56:45Z

Let's get rid of another follow_page() user and perform the conversion
under PTL: Note that this is also what follow_page_pte() ends up doing.

Unfortunately we cannot currently optimize out the additional reference,
because arch_make_folio_accessible() must be called with a raised
refcount to protect against concurrent conversion to secure. We can just
move the arch_make_folio_accessible() under the PTL, like
follow_page_pte() would.

We'll effectively drop the "writable" check implied by FOLL_WRITE:
follow_page_pte() would also not check that when calling
arch_make_folio_accessible(), so there is no good reason for doing that
here.

We'll lose the secretmem check from follow_page() as well, about which
we shouldn't really care about.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/s390/mm/fault.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 8e149ef5e89b..ad8b0d6b77ea 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -34,6 +34,7 @@
#include <linux/uaccess.h>
#include <linux/hugetlb.h>
#include <linux/kfence.h>
+#include <linux/pagewalk.h>
#include <asm/asm-extable.h>
#include <asm/asm-offsets.h>
#include <asm/ptrace.h>
@@ -492,9 +493,9 @@ void do_secure_storage_access(struct pt_regs *regs)
union teid teid = { .val = regs->int_parm_long };
unsigned long addr = get_fault_address(regs);
struct vm_area_struct *vma;
+ struct folio_walk fw;
struct mm_struct *mm;
struct folio *folio;
- struct page *page;
struct gmap *gmap;
int rc;

@@ -536,15 +537,18 @@ void do_secure_storage_access(struct pt_regs *regs)
vma = find_vma(mm, addr);
if (!vma)
return handle_fault_error(regs, SEGV_MAPERR);
- page = follow_page(vma, addr, FOLL_WRITE | FOLL_GET);
- if (IS_ERR_OR_NULL(page)) {
+ folio = folio_walk_start(&fw, vma, addr, 0);
+ if (!folio) {
mmap_read_unlock(mm);
break;
}
- folio = page_folio(page);
- if (arch_make_folio_accessible(folio))
- send_sig(SIGSEGV, current, 0);
+ /* arch_make_folio_accessible() needs a raised refcount. */
+ folio_get(folio);
+ rc = arch_make_folio_accessible(folio);
folio_put(folio);
+ folio_walk_end(&fw, vma);
+ if (rc)
+ send_sig(SIGSEGV, current, 0);
mmap_read_unlock(mm);
break;
case KERNEL_FAULT:
--
2.45.2