mm/memory: handle !page case in zap_present_pte() separately

We don't need uptodate accessed/dirty bits, so in theory we could replace
ptep_get_and_clear_full() by an optimized ptep_clear_full() function.
Let's rely on the provided pte.

Further, there is no scenario where we would have to insert uffd-wp
markers when zapping something that is not a normal page (i.e., zeropage).
Add a sanity check to make sure this remains true.

should_zap_folio() no longer has to handle NULL pointers.  This change
replaces 2/3 "!page/!folio" checks by a single "!page" one.

Note that arch_check_zapped_pte() on x86-64 checks the HW-dirty bit to
detect shadow stack entries.  But for shadow stack entries, the HW dirty
bit (in combination with non-writable PTEs) is set by software.  So for
the arch_check_zapped_pte() check, we don't have to sync against HW
setting the HW dirty bit concurrently, it is always set.

Link: https://lkml.kernel.org/r/20240214204435.167852-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 6712453888fa84652b1ab27f205b0db78aaf1785..2b1e9abbe1e09302b0bc63fa81dcb931d566cb97 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1499,10 +1499,6 @@ static inline bool should_zap_folio(struct zap_details *details,
        if (should_zap_cows(details))
                return true;
 
-       /* E.g. the caller passes NULL for the case of a zero folio */
-       if (!folio)
-               return true;
-
        /* Otherwise we should only zap non-anon folios */
        return !folio_test_anon(folio);
 }
@@ -1540,24 +1536,28 @@ static inline void zap_present_pte(struct mmu_gather *tlb,
                int *rss, bool *force_flush, bool *force_break)
 {
        struct mm_struct *mm = tlb->mm;
-       struct folio *folio = NULL;
        bool delay_rmap = false;
+       struct folio *folio;
        struct page *page;
 
        page = vm_normal_page(vma, addr, ptent);
-       if (page)
-               folio = page_folio(page);
+       if (!page) {
+               /* We don't need up-to-date accessed/dirty bits. */
+               ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
+               arch_check_zapped_pte(vma, ptent);
+               tlb_remove_tlb_entry(tlb, pte, addr);
+               VM_WARN_ON_ONCE(userfaultfd_wp(vma));
+               ksm_might_unmap_zero_page(mm, ptent);
+               return;
+       }
 
+       folio = page_folio(page);
        if (unlikely(!should_zap_folio(details, folio)))
                return;
        ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
        arch_check_zapped_pte(vma, ptent);
        tlb_remove_tlb_entry(tlb, pte, addr);
        zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
-       if (unlikely(!page)) {
-               ksm_might_unmap_zero_page(mm, ptent);
-               return;
-       }
 
        if (!folio_test_anon(folio)) {
                if (pte_dirty(ptent)) {