KVM: MIPS/Emulate: Use lockless GVA helpers for cache emulation

Use the lockless GVA helpers to implement the reading of guest
instructions for emulation. This will allow it to handle asynchronous
TLB flushes when they are implemented.

This is a little more complicated than the other two cases (get_inst()
and dynamic translation) due to the need to emulate the appropriate
guest TLB exception when the address isn't present or isn't valid in the
guest TLB.

Since there are several protected cache ops that may need to be
performed safely, this is abstracted by kvm_mips_guest_cache_op() which
is passed a protected cache op function pointer and takes care of the
lockless operation and fault handling / retry if the op should fail,
taking advantage of the new errors which the protected cache ops can now
return. This allows the existing advance fault handling which relied on
host TLB lookups to be removed, along with the now unused
kvm_mips_host_tlb_lookup(),

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

arch/mips/include/asm/kvm_host.h

@@ -226,6 +226,7 @@ enum emulation_result {
 	EMULATE_FAIL,		/* can't emulate this instruction */
 	EMULATE_WAIT,		/* WAIT instruction */
 	EMULATE_PRIV_FAIL,
+	EMULATE_EXCEPT,		/* A guest exception has been generated */
 };
 
 #define mips3_paddr_to_tlbpfn(x) \
@@ -614,7 +615,6 @@ extern int kvm_mips_host_tlb_inv(struct kvm_vcpu *vcpu, unsigned long entryhi,
 
 extern int kvm_mips_guest_tlb_lookup(struct kvm_vcpu *vcpu,
 				     unsigned long entryhi);
-extern int kvm_mips_host_tlb_lookup(struct kvm_vcpu *vcpu, unsigned long vaddr);
 
 void kvm_mips_suspend_mm(int cpu);
 void kvm_mips_resume_mm(int cpu);

arch/mips/kvm/emulate.c

@@ -1697,12 +1697,56 @@ enum emulation_result kvm_mips_emulate_load(union mips_instruction inst,
 	return er;
 }
 
+static enum emulation_result kvm_mips_guest_cache_op(int (*fn)(unsigned long),
+						     unsigned long curr_pc,
+						     unsigned long addr,
+						     struct kvm_run *run,
+						     struct kvm_vcpu *vcpu,
+						     u32 cause)
+{
+	int err;
+
+	for (;;) {
+		/* Carefully attempt the cache operation */
+		kvm_trap_emul_gva_lockless_begin(vcpu);
+		err = fn(addr);
+		kvm_trap_emul_gva_lockless_end(vcpu);
+
+		if (likely(!err))
+			return EMULATE_DONE;
+
+		/*
+		 * Try to handle the fault and retry, maybe we just raced with a
+		 * GVA invalidation.
+		 */
+		switch (kvm_trap_emul_gva_fault(vcpu, addr, false)) {
+		case KVM_MIPS_GVA:
+		case KVM_MIPS_GPA:
+			/* bad virtual or physical address */
+			return EMULATE_FAIL;
+		case KVM_MIPS_TLB:
+			/* no matching guest TLB */
+			vcpu->arch.host_cp0_badvaddr = addr;
+			vcpu->arch.pc = curr_pc;
+			kvm_mips_emulate_tlbmiss_ld(cause, NULL, run, vcpu);
+			return EMULATE_EXCEPT;
+		case KVM_MIPS_TLBINV:
+			/* invalid matching guest TLB */
+			vcpu->arch.host_cp0_badvaddr = addr;
+			vcpu->arch.pc = curr_pc;
+			kvm_mips_emulate_tlbinv_ld(cause, NULL, run, vcpu);
+			return EMULATE_EXCEPT;
+		default:
+			break;
+		};
+	}
+}
+
 enum emulation_result kvm_mips_emulate_cache(union mips_instruction inst,
 					     u32 *opc, u32 cause,
 					     struct kvm_run *run,
 					     struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
 	enum emulation_result er = EMULATE_DONE;
 	u32 cache, op_inst, op, base;
 	s16 offset;
@@ -1759,81 +1803,16 @@ enum emulation_result kvm_mips_emulate_cache(union mips_instruction inst,
 		goto done;
 	}
 
-	preempt_disable();
-	if (KVM_GUEST_KSEGX(va) == KVM_GUEST_KSEG0) {
-		if (kvm_mips_host_tlb_lookup(vcpu, va) < 0 &&
-		    kvm_mips_handle_kseg0_tlb_fault(va, vcpu)) {
-			kvm_err("%s: handling mapped kseg0 tlb fault for %lx, vcpu: %p, ASID: %#lx\n",
-				__func__, va, vcpu, read_c0_entryhi());
-			er = EMULATE_FAIL;
-			preempt_enable();
-			goto done;
-		}
-	} else if ((KVM_GUEST_KSEGX(va) < KVM_GUEST_KSEG0) ||
-		   KVM_GUEST_KSEGX(va) == KVM_GUEST_KSEG23) {
-		int index;
-
-		/* If an entry already exists then skip */
-		if (kvm_mips_host_tlb_lookup(vcpu, va) >= 0)
-			goto skip_fault;
-
-		/*
-		 * If address not in the guest TLB, then give the guest a fault,
-		 * the resulting handler will do the right thing
-		 */
-		index = kvm_mips_guest_tlb_lookup(vcpu, (va & VPN2_MASK) |
-						  (kvm_read_c0_guest_entryhi
-						   (cop0) & KVM_ENTRYHI_ASID));
-
-		if (index < 0) {
-			vcpu->arch.host_cp0_badvaddr = va;
-			vcpu->arch.pc = curr_pc;
-			er = kvm_mips_emulate_tlbmiss_ld(cause, NULL, run,
-							 vcpu);
-			preempt_enable();
-			goto dont_update_pc;
-		} else {
-			struct kvm_mips_tlb *tlb = &vcpu->arch.guest_tlb[index];
-			/*
-			 * Check if the entry is valid, if not then setup a TLB
-			 * invalid exception to the guest
-			 */
-			if (!TLB_IS_VALID(*tlb, va)) {
-				vcpu->arch.host_cp0_badvaddr = va;
-				vcpu->arch.pc = curr_pc;
-				er = kvm_mips_emulate_tlbinv_ld(cause, NULL,
-								run, vcpu);
-				preempt_enable();
-				goto dont_update_pc;
-			}
-			/*
-			 * We fault an entry from the guest tlb to the
-			 * shadow host TLB
-			 */
-			if (kvm_mips_handle_mapped_seg_tlb_fault(vcpu, tlb,
-								 va)) {
-				kvm_err("%s: handling mapped seg tlb fault for %lx, index: %u, vcpu: %p, ASID: %#lx\n",
-					__func__, va, index, vcpu,
-					read_c0_entryhi());
-				er = EMULATE_FAIL;
-				preempt_enable();
-				goto done;
-			}
-		}
-	} else {
-		kvm_err("INVALID CACHE INDEX/ADDRESS (cache: %#x, op: %#x, base[%d]: %#lx, offset: %#x\n",
-			cache, op, base, arch->gprs[base], offset);
-		er = EMULATE_FAIL;
-		preempt_enable();
-		goto done;
-
-	}
-
-skip_fault:
 	/* XXXKYMA: Only a subset of cache ops are supported, used by Linux */
 	if (op_inst == Hit_Writeback_Inv_D || op_inst == Hit_Invalidate_D) {
-		protected_writeback_dcache_line(va);
-
+		/*
+		 * Perform the dcache part of icache synchronisation on the
+		 * guest's behalf.
+		 */
+		er = kvm_mips_guest_cache_op(protected_writeback_dcache_line,
+					     curr_pc, va, run, vcpu, cause);
+		if (er != EMULATE_DONE)
+			goto done;
 #ifdef CONFIG_KVM_MIPS_DYN_TRANS
 		/*
 		 * Replace the CACHE instruction, with a SYNCI, not the same,
@@ -1842,8 +1821,15 @@ skip_fault:
 		kvm_mips_trans_cache_va(inst, opc, vcpu);
 #endif
 	} else if (op_inst == Hit_Invalidate_I) {
-		protected_writeback_dcache_line(va);
-		protected_flush_icache_line(va);
+		/* Perform the icache synchronisation on the guest's behalf */
+		er = kvm_mips_guest_cache_op(protected_writeback_dcache_line,
+					     curr_pc, va, run, vcpu, cause);
+		if (er != EMULATE_DONE)
+			goto done;
+		er = kvm_mips_guest_cache_op(protected_flush_icache_line,
+					     curr_pc, va, run, vcpu, cause);
+		if (er != EMULATE_DONE)
+			goto done;
 
 #ifdef CONFIG_KVM_MIPS_DYN_TRANS
 		/* Replace the CACHE instruction, with a SYNCI */
@@ -1855,17 +1841,13 @@ skip_fault:
 		er = EMULATE_FAIL;
 	}
 
-	preempt_enable();
 done:
 	/* Rollback PC only if emulation was unsuccessful */
 	if (er == EMULATE_FAIL)
 		vcpu->arch.pc = curr_pc;
-
-dont_update_pc:
-	/*
-	 * This is for exceptions whose emulation updates the PC, so do not
-	 * overwrite the PC under any circumstances
-	 */
+	/* Guest exception needs guest to resume */
+	if (er == EMULATE_EXCEPT)
+		er = EMULATE_DONE;
 
 	return er;
 }

arch/mips/kvm/tlb.c

@@ -117,41 +117,6 @@ int kvm_mips_guest_tlb_lookup(struct kvm_vcpu *vcpu, unsigned long entryhi)
 }
 EXPORT_SYMBOL_GPL(kvm_mips_guest_tlb_lookup);
 
-int kvm_mips_host_tlb_lookup(struct kvm_vcpu *vcpu, unsigned long vaddr)
-{
-	unsigned long old_entryhi, flags;
-	int idx;
-
-	local_irq_save(flags);
-
-	old_entryhi = read_c0_entryhi();
-
-	if (KVM_GUEST_KERNEL_MODE(vcpu))
-		write_c0_entryhi((vaddr & VPN2_MASK) |
-				 kvm_mips_get_kernel_asid(vcpu));
-	else {
-		write_c0_entryhi((vaddr & VPN2_MASK) |
-				 kvm_mips_get_user_asid(vcpu));
-	}
-
-	mtc0_tlbw_hazard();
-
-	tlb_probe();
-	tlb_probe_hazard();
-	idx = read_c0_index();
-
-	/* Restore old ASID */
-	write_c0_entryhi(old_entryhi);
-	mtc0_tlbw_hazard();
-
-	local_irq_restore(flags);
-
-	kvm_debug("Host TLB lookup, %#lx, idx: %2d\n", vaddr, idx);
-
-	return idx;
-}
-EXPORT_SYMBOL_GPL(kvm_mips_host_tlb_lookup);
-
 static int _kvm_mips_host_tlb_inv(unsigned long entryhi)
 {
 	int idx;