From bb67bf75fb6ebd3bd207d91246bdc76d5ce371b3 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Fri, 30 Aug 2024 08:27:20 +0000
Subject: [PATCH] arm64: Implement
 VMSAv8TranslationMap::ClearAccessedAndModified

* Heavily inspired by the RISC-V equivalent.

Change-Id: I7d2ed14fb0a246223a23f7df659b6006326a7013
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8155
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>
Haiku-Format: Haiku-format Bot <no-reply+haikuformatbot@haiku-os.org>
---
 .../arch/arm64/VMSAv8TranslationMap.cpp       | 48 ++++++++++++++++++-
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/src/system/kernel/arch/arm64/VMSAv8TranslationMap.cpp b/src/system/kernel/arch/arm64/VMSAv8TranslationMap.cpp
index be19285a36..30bd4d86eb 100644
--- a/src/system/kernel/arch/arm64/VMSAv8TranslationMap.cpp
+++ b/src/system/kernel/arch/arm64/VMSAv8TranslationMap.cpp
@@ -840,8 +840,52 @@ bool
 VMSAv8TranslationMap::ClearAccessedAndModified(
 	VMArea* area, addr_t address, bool unmapIfUnaccessed, bool& _modified)
 {
-	panic("VMSAv8TranslationMap::ClearAccessedAndModified not implemented\n");
-	return B_OK;
+	RecursiveLocker locker(fLock);
+	ThreadCPUPinner pinner(thread_get_current_thread());
+
+	uint64_t pageMask = (1UL << fPageBits) - 1;
+	uint64_t vaMask = (1UL << fVaBits) - 1;
+
+	ASSERT((address & pageMask) == 0);
+	ASSERT(ValidateVa(address));
+
+	uint64_t oldPte = 0;
+	ProcessRange(fPageTable, 0, address & vaMask, B_PAGE_SIZE, nullptr,
+		[=, &_modified, &oldPte](uint64_t* ptePtr, uint64_t effectiveVa) {
+			// We need to use an atomic compare-swap loop because we must
+			// first read the old PTE and make decisions based on the AF
+			// bit to proceed.
+			while (true) {
+				oldPte = atomic_get64((int64_t*)ptePtr);
+				uint64_t newPte = oldPte & ~kAttrAF;
+				newPte |= kAttrAPReadOnly;
+
+				// If the page has been not be accessed, then unmap it.
+				if (unmapIfUnaccessed && (oldPte & kAttrAF) == 0)
+					newPte = 0;
+
+				if ((uint64_t)atomic_test_and_set64((int64_t*)ptePtr, newPte, oldPte) == oldPte)
+					break;
+			}
+			asm("dsb ishst"); // Ensure PTE write completed
+		});
+
+	pinner.Unlock();
+	_modified = (oldPte & kAttrAPReadOnly) == 0;
+	if ((oldPte & kAttrAF) != 0) {
+		FlushVAFromTLBByASID(address);
+		return true;
+	}
+
+	if (!unmapIfUnaccessed)
+		return false;
+
+	fMapCount--;
+
+	locker.Detach(); // UnaccessedPageUnmapped takes ownership
+	phys_addr_t oldPa = oldPte & kPteAddrMask;
+	UnaccessedPageUnmapped(area, oldPa >> fPageBits);
+	return false;
 }