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

Claudio Imbrenda
2024-08-07T09:18:35Z

On Fri, 2 Aug 2024 17:55:22 +0200
David Hildenbrand <david@redhat.com> wrote:

> 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>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.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;