arch-arm: Check cache maintenance insts for permission faults

In AArch32, data cache maintenance instructions that operate by VA do
not generate permission faults.

In AArch64, a data cache invalidate instruction can generate a
permission fault when there are no write permissions to the specified
VA. Data cache clean and data cache clean and invalidate instructions
do not generate permission faults.

Checks for external aborts are also bypassed for data cache
maintenance instructions.

Change-Id: Iea5bc665e4cf66d528e36b671535b66637c4b224
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/7827
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/src/arch/arm/tlb.cc b/src/arch/arm/tlb.cc
index 3aebe3d59..aeaf60bdd 100644
--- a/src/arch/arm/tlb.cc
+++ b/src/arch/arm/tlb.cc
@@ -603,6 +603,12 @@ TLB::translateSe(RequestPtr req, ThreadContext *tc, Mode mode,
 Fault
 TLB::checkPermissions(TlbEntry *te, RequestPtr req, Mode mode)
 {
+    // a data cache maintenance instruction that operates by MVA does
+    // not generate a Data Abort exeception due to a Permission fault
+    if (req->isCacheMaintenance()) {
+        return NoFault;
+    }
+
     Addr vaddr = req->getVaddr(); // 32-bit don't have to purify
     Request::Flags flags = req->getFlags();
     bool is_fetch  = (mode == Execute);
@@ -778,12 +784,22 @@ TLB::checkPermissions64(TlbEntry *te, RequestPtr req, Mode mode,
 {
     assert(aarch64);
 
+    // A data cache maintenance instruction that operates by VA does
+    // not generate a Permission fault unless:
+    // * It is a data cache invalidate (dc ivac) which requires write
+    //   permissions to the VA, or
+    // * It is executed from EL0
+    if (req->isCacheClean() && aarch64EL != EL0 && !isStage2) {
+        return NoFault;
+    }
+
     Addr vaddr_tainted = req->getVaddr();
     Addr vaddr = purifyTaggedAddr(vaddr_tainted, tc, aarch64EL, ttbcr);
 
     Request::Flags flags = req->getFlags();
     bool is_fetch  = (mode == Execute);
-    bool is_write  = (mode == Write);
+    // Cache clean operations require read permissions to the specified VA
+    bool is_write = !req->isCacheClean() && mode == Write;
     bool is_priv M5_VAR_USED  = isPriv && !(flags & UserMode);
 
     updateMiscReg(tc, curTranType);
@@ -1528,7 +1544,8 @@ TLB::setTestInterface(SimObject *_ti)
 Fault
 TLB::testTranslation(RequestPtr req, Mode mode, TlbEntry::DomainType domain)
 {
-    if (!test || !req->hasSize() || req->getSize() == 0) {
+    if (!test || !req->hasSize() || req->getSize() == 0 ||
+        req->isCacheMaintenance()) {
         return NoFault;
     } else {
         return test->translationCheck(req, isPriv, mode, domain);