Subject: [PATCH v3 25/32] arm64: KVM: 32bit conditional execution emulation

From: [email-masked] (Marc Zyngier)
Date: Wed, 24 Apr 2013 14:13:37 +0100

On 24/04/13 00:00, Christoffer Dall wrote:
> On Mon, Apr 08, 2013 at 05:17:27PM +0100, Marc Zyngier wrote:
>> As conditional instructions can trap on AArch32, add the thinest
>> possible emulation layer to keep 32bit guests happy.
>>
>> Reviewed-by: Christopher Covington <[email-masked]>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  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 37a6567..8d4ab33 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(const struct kvm_vcpu *vcpu, u8 reg_num);
>>  unsigned long *vcpu_spsr32(const struct kvm_vcpu *vcpu);
>>  
>> +bool kvm_condition_valid32(const 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);
>> @@ -57,12 +60,18 @@ static inline bool vcpu_mode_is_32bit(const struct kvm_vcpu *vcpu)
>>  
>>  static inline bool kvm_condition_valid(const 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 1668448..88c6639 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -11,7 +11,7 @@ obj-$(CONFIG_KVM_ARM_HOST) += kvm.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(addprefix ../../../virt/kvm/, kvm_main.o coalesced_mmio.o)
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(addprefix ../../../arch/arm/kvm/, arm.o mmu.o mmio.o psci.o perf.o)
>>  
>> -kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o
>> +kvm-$(CONFIG_KVM_ARM_HOST) += emulate.o inject_fault.o regmap.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += guest.o reset.o sys_regs.o sys_regs_generic_v8.o
>>  
>> diff --git a/arch/arm64/kvm/emulate.c b/arch/arm64/kvm/emulate.c
>> new file mode 100644
>> index 0000000..01d4713
>> --- /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 <[email-masked]>
> 
> don't you want to add yourself here?

There's really nothing I actually wrote here. Most of it is your code,
and the rest comes from other parts of arch/arm.

I guess I could always mention myself for the ESR_EL2_* macros... ;-)

>> + *
>> + * 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(const 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(const 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
> 
> s/advanved/advanced/

See? You actually hold the copyright on that spelling mistake! ;-)
> 
>> + * 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) */
> 
> That's actually page A2-52 to be a little more precise...

Yup. Feel free to update the 32bit code as well... ;-)

>> +	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);
> 
> again we don't need the '!!' when it's a bool.

I'm still not prepared to consider a bitwise and as a bool, and I'm
happy for the !! to make the conversion to a bool completely obvious.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...