[PATCH v5 5/5] KVM: PPC: Book3s: mmio: Deliver DSI after emulation failure

From: Fabiano Rosas <farosas@linux.ibm.com>
To: kvm-ppc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, aik@ozlabs.ru
Subject: [PATCH v5 5/5] KVM: PPC: Book3s: mmio: Deliver DSI after emulation failure
Date: Tue, 25 Jan 2022 18:56:55 -0300	[thread overview]
Message-ID: <20220125215655.1026224-6-farosas@linux.ibm.com> (raw)
In-Reply-To: <20220125215655.1026224-1-farosas@linux.ibm.com>

MMIO emulation can fail if the guest uses an instruction that we are
not prepared to emulate. Since these instructions can be and most
likely are valid ones, this is (slightly) closer to an access fault
than to an illegal instruction, so deliver a Data Storage interrupt
instead of a Program interrupt.

BookE ignores bad faults, so it will keep using a Program interrupt
because a DSI would cause a fault loop in the guest.

Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
---
 arch/powerpc/kvm/emulate_loadstore.c | 10 +++-------
 arch/powerpc/kvm/powerpc.c           | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kvm/emulate_loadstore.c b/arch/powerpc/kvm/emulate_loadstore.c
index 48272a9b9c30..cfc9114b87d0 100644
--- a/arch/powerpc/kvm/emulate_loadstore.c
+++ b/arch/powerpc/kvm/emulate_loadstore.c
@@ -73,7 +73,6 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
 {
 	u32 inst;
 	enum emulation_result emulated = EMULATE_FAIL;
-	int advance = 1;
 	struct instruction_op op;
 
 	/* this default type might be overwritten by subcategories */
@@ -98,6 +97,8 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
 		int type = op.type & INSTR_TYPE_MASK;
 		int size = GETSIZE(op.type);
 
+		vcpu->mmio_is_write = OP_IS_STORE(type);
+
 		switch (type) {
 		case LOAD:  {
 			int instr_byte_swap = op.type & BYTEREV;
@@ -355,15 +356,10 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	if (emulated == EMULATE_FAIL) {
-		advance = 0;
-		kvmppc_core_queue_program(vcpu, 0);
-	}
-
 	trace_kvm_ppc_instr(inst, kvmppc_get_pc(vcpu), emulated);
 
 	/* Advance past emulated instruction. */
-	if (advance)
+	if (emulated != EMULATE_FAIL)
 		kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
 
 	return emulated;
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index acb0d2a4bdb9..82d889db2b6b 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -309,6 +309,28 @@ int kvmppc_emulate_mmio(struct kvm_vcpu *vcpu)
 		kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
 		kvm_debug_ratelimited("Guest access to device memory using unsupported instruction (opcode: %#08x)\n",
 				      last_inst);
+
+		/*
+		 * Injecting a Data Storage here is a bit more
+		 * accurate since the instruction that caused the
+		 * access could still be a valid one.
+		 */
+		if (!IS_ENABLED(CONFIG_BOOKE)) {
+			ulong dsisr = DSISR_BADACCESS;
+
+			if (vcpu->mmio_is_write)
+				dsisr |= DSISR_ISSTORE;
+
+			kvmppc_core_queue_data_storage(vcpu, vcpu->arch.vaddr_accessed, dsisr);
+		} else {
+			/*
+			 * BookE does not send a SIGBUS on a bad
+			 * fault, so use a Program interrupt instead
+			 * to avoid a fault loop.
+			 */
+			kvmppc_core_queue_program(vcpu, 0);
+		}
+
 		r = RESUME_GUEST;
 		break;
 	}
-- 
2.34.1

