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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	kvm-ppc@vger.kernel.org
Cc: npiggin@gmail.com, paulus@ozlabs.org, leonardo@linux.ibm.com,
	kirill@shutemov.name,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Subject: [PATCH v3 03/22] powerpc/mm/hash64: use _PAGE_PTE when checking for pte_present
Date: Mon, 20 Apr 2020 18:14:15 +0530	[thread overview]
Message-ID: <20200420124434.47330-4-aneesh.kumar@linux.ibm.com> (raw)
In-Reply-To: <20200420124434.47330-1-aneesh.kumar@linux.ibm.com>

This makes the pte_present check stricter by checking for additional _PAGE_PTE
bit. A level 1 pte pointer (THP pte) can be switched to a pointer to level 0 pte
page table page by following two operations.

1) THP split.
2) madvise(MADV_DONTNEED) in parallel to page fault.

A lockless page table walk need to make sure we can handle such changes
gracefully.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 15 ++++++++++-----
 arch/powerpc/mm/book3s64/hash_utils.c        | 11 +++++++++--
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 368b136517e0..03521a8b0292 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -553,6 +553,12 @@ static inline pte_t pte_clear_savedwrite(pte_t pte)
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
+static inline bool pte_hw_valid(pte_t pte)
+{
+	return (pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE)) ==
+		cpu_to_be64(_PAGE_PRESENT | _PAGE_PTE);
+}
+
 static inline int pte_present(pte_t pte)
 {
 	/*
@@ -561,12 +567,11 @@ static inline int pte_present(pte_t pte)
 	 * invalid during ptep_set_access_flags. Hence we look for _PAGE_INVALID
 	 * if we find _PAGE_PRESENT cleared.
 	 */
-	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_INVALID));
-}
 
-static inline bool pte_hw_valid(pte_t pte)
-{
-	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT));
+	if (pte_hw_valid(pte))
+		return true;
+	return (pte_raw(pte) & cpu_to_be64(_PAGE_INVALID | _PAGE_PTE)) ==
+		cpu_to_be64(_PAGE_INVALID | _PAGE_PTE);
 }
 
 #ifdef CONFIG_PPC_MEM_KEYS
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index e951e87a974d..525eac4ee2c2 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -1350,8 +1350,15 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
 		goto bail;
 	}
 
-	/* Add _PAGE_PRESENT to the required access perm */
-	access |= _PAGE_PRESENT;
+	/*
+	 * Add _PAGE_PRESENT to the required access perm. If there are parallel
+	 * updates to the pte that can possibly clear _PAGE_PTE, catch that too.
+	 *
+	 * We can safely use the return pte address in rest of the function
+	 * because we do set H_PAGE_BUSY which prevents further updates to pte
+	 * from generic code.
+	 */
+	access |= _PAGE_PRESENT | _PAGE_PTE;
 
 	/*
 	 * Pre-check access permissions (will be re-checked atomically
-- 
2.25.3



  parent reply	other threads:[~2020-04-20 12:45 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-20 12:44 [PATCH v3 00/22] Avoid IPI while updating page table entries Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 01/22] powerpc/pkeys: Avoid using lockless page table walk Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 02/22] powerpc/pkeys: Check vma before returning key fault error to the user Aneesh Kumar K.V
2020-04-20 12:44 ` Aneesh Kumar K.V [this message]
2020-04-20 12:44 ` [PATCH v3 04/22] powerpc/hash64: Restrict page table lookup using init_mm with __flush_hash_table_range Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 05/22] powerpc/book3s64/hash: Use the pte_t address from the caller Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 06/22] powerpc/mce: Don't reload pte val in addr_to_pfn Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 07/22] powerpc/perf/callchain: Use __get_user_pages_fast in read_user_stack_slow Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 08/22] powerpc/kvm/book3s: switch from raw_spin_*lock to arch_spin_lock Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 09/22] powerpc/kvm/book3s: Add helper to walk partition scoped linux page table Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 10/22] powerpc/kvm/nested: Add helper to walk nested shadow " Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 11/22] powerpc/kvm/book3s: Use kvm helpers to walk shadow or secondary table Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 12/22] powerpc/kvm/book3s: Add helper for host page table walk Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 13/22] powerpc/kvm/book3s: Use find_kvm_host_pte in page fault handler Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 14/22] powerpc/kvm/book3s: Use find_kvm_host_pte in h_enter Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 17/22] powerpc/kvm/book3s: use find_kvm_host_pte in kvmppc_book3s_instantiate_page Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 18/22] powerpc/kvm/book3s: Use find_kvm_host_pte in kvmppc_get_hpa Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 19/22] powerpc/kvm/book3s: Use pte_present instead of opencoding _PAGE_PRESENT check Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 20/22] powerpc/mm/book3s64: Avoid sending IPI on clearing PMD Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 21/22] mm: change pmdp_huge_get_and_clear_full take vm_area_struct as arg Aneesh Kumar K.V
2020-04-20 12:44 ` [PATCH v3 22/22] powerpc/mm/book3s64: Fix MADV_DONTNEED and parallel page fault race Aneesh Kumar K.V

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