linux-kernel - [PATCH v4 31/33] powerc/mm: try VMA lock-based page fault handling first

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Message-ID: <20230227173632.3292573-32-surenb@google.com>
Date:   Mon, 27 Feb 2023 09:36:30 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
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        Suren Baghdasaryan <surenb@...gle.com>
Subject: [PATCH v4 31/33] powerc/mm: try VMA lock-based page fault handling first

From: Laurent Dufour <ldufour@...ux.ibm.com>

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails.
Copied from "x86/mm: try VMA lock-based page fault handling first"

Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 arch/powerpc/mm/fault.c                | 41 ++++++++++++++++++++++++++
 arch/powerpc/platforms/powernv/Kconfig |  1 +
 arch/powerpc/platforms/pseries/Kconfig |  1 +
 3 files changed, 43 insertions(+)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 2bef19cc1b98..c7ae86b04b8a 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -469,6 +469,44 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 	if (is_exec)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+#ifdef CONFIG_PER_VMA_LOCK
+	if (!(flags & FAULT_FLAG_USER))
+		goto lock_mmap;
+
+	vma = lock_vma_under_rcu(mm, address);
+	if (!vma)
+		goto lock_mmap;
+
+	if (unlikely(access_pkey_error(is_write, is_exec,
+				       (error_code & DSISR_KEYFAULT), vma))) {
+		int rc = bad_access_pkey(regs, address, vma);
+
+		vma_end_read(vma);
+		return rc;
+	}
+
+	if (unlikely(access_error(is_write, is_exec, vma))) {
+		int rc = bad_access(regs, address);
+
+		vma_end_read(vma);
+		return rc;
+	}
+
+	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
+	vma_end_read(vma);
+
+	if (!(fault & VM_FAULT_RETRY)) {
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		goto done;
+	}
+	count_vm_vma_lock_event(VMA_LOCK_RETRY);
+
+	if (fault_signal_pending(fault, regs))
+		return user_mode(regs) ? 0 : SIGBUS;
+
+lock_mmap:
+#endif /* CONFIG_PER_VMA_LOCK */
+
 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
@@ -545,6 +583,9 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	mmap_read_unlock(current->mm);
 
+#ifdef CONFIG_PER_VMA_LOCK
+done:
+#endif
 	if (unlikely(fault & VM_FAULT_ERROR))
 		return mm_fault_error(regs, address, fault);
 
diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index ae248a161b43..70a46acc70d6 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig
@@ -16,6 +16,7 @@ config PPC_POWERNV
 	select PPC_DOORBELL
 	select MMU_NOTIFIER
 	select FORCE_SMP
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	default y
 
 config OPAL_PRD
diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index b481c5c8bae1..9c205fe0e619 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -21,6 +21,7 @@ config PPC_PSERIES
 	select HOTPLUG_CPU
 	select FORCE_SMP
 	select SWIOTLB
+	select ARCH_SUPPORTS_PER_VMA_LOCK
 	default y
 
 config PARAVIRT
-- 
2.39.2.722.g9855ee24e9-goog