Re: [PATCH 15/23] s390: allow pte_offset_map_lock() to fail
From: Claudio Imbrenda <imbrenda@linux.ibm.com>
Date: 2023-05-17 10:41:16
Also in:
linux-arm-kernel, linux-m68k, linux-mips, linux-mm, linux-riscv, linux-s390, linux-sh, lkml, sparclinux
On Tue, 9 May 2023 22:01:16 -0700 (PDT) Hugh Dickins [off-list ref] wrote:
quoted hunk ↗ jump to hunk
In rare transient cases, not yet made possible, pte_offset_map() and pte_offset_map_lock() may not find a page table: handle appropriately. Signed-off-by: Hugh Dickins <hughd@google.com> --- arch/s390/kernel/uv.c | 2 ++ arch/s390/mm/gmap.c | 2 ++ arch/s390/mm/pgtable.c | 12 +++++++++--- 3 files changed, 13 insertions(+), 3 deletions(-)diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c index cb2ee06df286..3c62d1b218b1 100644 --- a/arch/s390/kernel/uv.c +++ b/arch/s390/kernel/uv.c@@ -294,6 +294,8 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) rc = -ENXIO; ptep = get_locked_pte(gmap->mm, uaddr, &ptelock); + if (!ptep) + goto out; if (pte_present(*ptep) && !(pte_val(*ptep) & _PAGE_INVALID) && pte_write(*ptep)) { page = pte_page(*ptep); rc = -EAGAIN;diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index dc90d1eb0d55..d198fc9475a2 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c@@ -2549,6 +2549,8 @@ static int __zap_zero_pages(pmd_t *pmd, unsigned long start, spinlock_t *ptl; ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); + if (!ptep) + break;
so if pte_offset_map_lock fails, we abort and skip both the failed
entry and the rest of the entries?
can pte_offset_map_lock be retried immediately if it fails? (consider
that we currently don't allow THP with KVM guests)
Would something like this:
do {
ptep = pte_offset_map_lock(...);
mb(); /* maybe? */
} while (!ptep);
make sense?
otherwise maybe it's better to return an error and retry the whole
walk_page_range() in s390_enable_sie() ? it's a slow path anyway.
if (is_zero_pfn(pte_pfn(*ptep))) ptep_xchg_direct(walk->mm, addr, ptep, __pte(_PAGE_INVALID)); pte_unmap_unlock(ptep, ptl);
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