[PATCH 24/29] arm64: KVM: 32bit conditional execution emulation

Marc Zyngier
2013-03-05T03:55:44Z

As conditionnal instructions can trap on AArch32, add the thinest
possible emulation layer to keep 32bit guests happy.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/include/asm/kvm_emulate.h | 13 ++-
arch/arm64/kvm/Makefile | 2 +-
arch/arm64/kvm/emulate.c | 154 +++++++++++++++++++++++++++++++++++
3 files changed, 166 insertions(+), 3 deletions(-)
create mode 100644 arch/arm64/kvm/emulate.c

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 2e72a4f..4d5e0ee 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -31,6 +31,9 @@
unsigned long *vcpu_reg32(struct kvm_vcpu *vcpu, u8 reg_num);
unsigned long *vcpu_spsr32(struct kvm_vcpu *vcpu);

+bool kvm_condition_valid32(struct kvm_vcpu *vcpu);
+void kvm_skip_instr32(struct kvm_vcpu *vcpu, bool is_wide_instr);
+
void kvm_inject_undefined(struct kvm_vcpu *vcpu);
void kvm_inject_dabt(struct kvm_vcpu *vcpu, unsigned long addr);
void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr);
@@ -52,12 +55,18 @@ static inline bool vcpu_mode_is_32bit(struct kvm_vcpu *vcpu)

static inline bool kvm_condition_valid(struct kvm_vcpu *vcpu)
{
- return true; /* No conditionals on arm64 */
+ if (vcpu_mode_is_32bit(vcpu))
+ return kvm_condition_valid32(vcpu);
+
+ return true;
}

static inline void kvm_skip_instr(struct kvm_vcpu *vcpu, bool is_wide_instr)
{
- *vcpu_pc(vcpu) += 4;
+ if (vcpu_mode_is_32bit(vcpu))
+ kvm_skip_instr32(vcpu, is_wide_instr);
+ else
+ *vcpu_pc(vcpu) += 4;
}

static inline void vcpu_set_thumb(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 50f9da0..a6ba0d8 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -10,7 +10,7 @@ obj-$(CONFIG_KVM_ARM_HOST) += $(addprefix ../../../virt/kvm/, kvm_main.o coalesc

obj-$(CONFIG_KVM_ARM_HOST) += $(addprefix ../../../arch/arm/kvm/, arm.o mmu.o mmio.o psci.o perf.o)

-obj-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o
+obj-$(CONFIG_KVM_ARM_HOST) += emulate.o inject_fault.o regmap.o
obj-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o idmap.o
obj-$(CONFIG_KVM_ARM_HOST) += guest.o reset.o sys_regs.o sys_regs_a57.o

diff --git a/arch/arm64/kvm/emulate.c b/arch/arm64/kvm/emulate.c
new file mode 100644
index 0000000..6b3dbc3
--- /dev/null
+++ b/arch/arm64/kvm/emulate.c
@@ -0,0 +1,154 @@
+/*
+ * (not much of an) Emulation layer for 32bit guests.
+ *
+ * Copyright (C) 2012 - Virtual Open Systems and Columbia University
+ * Author: Christoffer Dall <c.dall@virtualopensystems.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kvm_host.h>
+#include <asm/kvm_emulate.h>
+
+/*
+ * stolen from arch/arm/kernel/opcodes.c
+ *
+ * condition code lookup table
+ * index into the table is test code: EQ, NE, ... LT, GT, AL, NV
+ *
+ * bit position in short is condition code: NZCV
+ */
+static const unsigned short cc_map[16] = {
+ 0xF0F0, /* EQ == Z set */
+ 0x0F0F, /* NE */
+ 0xCCCC, /* CS == C set */
+ 0x3333, /* CC */
+ 0xFF00, /* MI == N set */
+ 0x00FF, /* PL */
+ 0xAAAA, /* VS == V set */
+ 0x5555, /* VC */
+ 0x0C0C, /* HI == C set && Z clear */
+ 0xF3F3, /* LS == C clear || Z set */
+ 0xAA55, /* GE == (N==V) */
+ 0x55AA, /* LT == (N!=V) */
+ 0x0A05, /* GT == (!Z && (N==V)) */
+ 0xF5FA, /* LE == (Z || (N!=V)) */
+ 0xFFFF, /* AL always */
+ 0 /* NV */
+};
+
+static int kvm_vcpu_get_condition(struct kvm_vcpu *vcpu)
+{
+ u32 esr = kvm_vcpu_get_hsr(vcpu);
+
+ if (esr & ESR_EL2_CV)
+ return (esr & ESR_EL2_COND) >> ESR_EL2_COND_SHIFT;
+
+ return -1;
+}
+
+/*
+ * Check if a trapped instruction should have been executed or not.
+ */
+bool kvm_condition_valid32(struct kvm_vcpu *vcpu)
+{
+ unsigned long cpsr;
+ u32 cpsr_cond;
+ int cond;
+
+ /* Top two bits non-zero? Unconditional. */
+ if (kvm_vcpu_get_hsr(vcpu) >> 30)
+ return true;
+
+ /* Is condition field valid? */
+ cond = kvm_vcpu_get_condition(vcpu);
+ if (cond == 0xE)
+ return true;
+
+ cpsr = *vcpu_cpsr(vcpu);
+
+ if (cond < 0) {
+ /* This can happen in Thumb mode: examine IT state. */
+ unsigned long it;
+
+ it = ((cpsr >> 8) & 0xFC) | ((cpsr >> 25) & 0x3);
+
+ /* it == 0 => unconditional. */
+ if (it == 0)
+ return true;
+
+ /* The cond for this insn works out as the top 4 bits. */
+ cond = (it >> 4);
+ }
+
+ cpsr_cond = cpsr >> 28;
+
+ if (!((cc_map[cond] >> cpsr_cond) & 1))
+ return false;
+
+ return true;
+}
+
+/**
+ * adjust_itstate - adjust ITSTATE when emulating instructions in IT-block
+ * @vcpu: The VCPU pointer
+ *
+ * When exceptions occur while instructions are executed in Thumb IF-THEN
+ * blocks, the ITSTATE field of the CPSR is not advanved (updated), so we have
+ * to do this little bit of work manually. The fields map like this:
+ *
+ * IT[7:0] -> CPSR[26:25],CPSR[15:10]
+ */
+static void kvm_adjust_itstate(struct kvm_vcpu *vcpu)
+{
+ unsigned long itbits, cond;
+ unsigned long cpsr = *vcpu_cpsr(vcpu);
+ bool is_arm = !(cpsr & COMPAT_PSR_T_BIT);
+
+ BUG_ON(is_arm && (cpsr & COMPAT_PSR_IT_MASK));
+
+ if (!(cpsr & COMPAT_PSR_IT_MASK))
+ return;
+
+ cond = (cpsr & 0xe000) >> 13;
+ itbits = (cpsr & 0x1c00) >> (10 - 2);
+ itbits |= (cpsr & (0x3 << 25)) >> 25;
+
+ /* Perform ITAdvance (see page A-52 in ARM DDI 0406C) */
+ if ((itbits & 0x7) == 0)
+ itbits = cond = 0;
+ else
+ itbits = (itbits << 1) & 0x1f;
+
+ cpsr &= ~COMPAT_PSR_IT_MASK;
+ cpsr |= cond << 13;
+ cpsr |= (itbits & 0x1c) << (10 - 2);
+ cpsr |= (itbits & 0x3) << 25;
+ *vcpu_cpsr(vcpu) = cpsr;
+}
+
+/**
+ * kvm_skip_instr - skip a trapped instruction and proceed to the next
+ * @vcpu: The vcpu pointer
+ */
+void kvm_skip_instr32(struct kvm_vcpu *vcpu, bool is_wide_instr)
+{
+ bool is_thumb;
+
+ is_thumb = !!(*vcpu_cpsr(vcpu) & COMPAT_PSR_T_BIT);
+ if (is_thumb && !is_wide_instr)
+ *vcpu_pc(vcpu) += 2;
+ else
+ *vcpu_pc(vcpu) += 4;
+ kvm_adjust_itstate(vcpu);
+}
--
1.7.12.4