s390/mm/fault: convert do_secure_storage_access() from follow_page() to folio_walk

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.

Link: https://lkml.kernel.org/r/20240802155524.517137-10-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 8e149ef5e89ba8abf4b4fee35f4c2a9f5bd0d218..ad8b0d6b77ea16a6e6f7a8beec405ecca77022fe 100644 (file)
--- 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: