Subject: [PATCH v3 1/2] arm/arm64: KVM: MMIO support for BE guest

From: [email-masked] (Marc Zyngier)
Date: Thu, 07 Nov 2013 17:18:50 +0000

On 07/11/13 05:10, Christoffer Dall wrote:
> On Tue, Nov 05, 2013 at 06:58:14PM +0000, Marc Zyngier wrote:
>> Do the necessary byteswap when host and guest have different
>> views of the universe. Actually, the only case we need to take
>> care of is when the guest is BE. All the other cases are naturally
>> handled.
>>
>> Also be careful about endianness when the data is being memcopy-ed
>> from/to the run buffer.
>>
>> Cc: Christoffer Dall <[email-masked]>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  arch/arm/include/asm/kvm_emulate.h   | 41 +++++++++++++++++
>>  arch/arm/kvm/mmio.c                  | 87 +++++++++++++++++++++++++++++++-----
>>  arch/arm64/include/asm/kvm_emulate.h | 48 ++++++++++++++++++++
>>  3 files changed, 165 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
>> index a464e8d..8a6be05 100644
>> --- a/arch/arm/include/asm/kvm_emulate.h
>> +++ b/arch/arm/include/asm/kvm_emulate.h
>> @@ -157,4 +157,45 @@ static inline u32 kvm_vcpu_hvc_get_imm(struct kvm_vcpu *vcpu)
>>  	return kvm_vcpu_get_hsr(vcpu) & HSR_HVC_IMM_MASK;
>>  }
>>  
>> +static inline bool kvm_vcpu_is_be(struct kvm_vcpu *vcpu)
>> +{
>> +	return !!(*vcpu_cpsr(vcpu) & PSR_E_BIT);
>> +}
>> +
>> +static inline unsigned long vcpu_data_guest_to_host(struct kvm_vcpu *vcpu,
>> +						    unsigned long data,
>> +						    unsigned int len)
>> +{
>> +	if (kvm_vcpu_is_be(vcpu)) {
>> +		switch (len) {
>> +		case 1:
>> +			return data & 0xff;
> 
> why are these masks necessary again?  For a writeb there should be no
> byteswapping on the guest side right?

They are not strictly mandatory, but I feel a lot more confident
trimming what we found in the register to the bare minimum.

>> +		case 2:
>> +			return be16_to_cpu(data & 0xffff);
>> +		default:
>> +			return be32_to_cpu(data);
>> +		}
>> +	}
>> +
>> +	return data;		/* Leave LE untouched */
>> +}
>> +
>> +static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>> +						    unsigned long data,
>> +						    unsigned int len)
>> +{
>> +	if (kvm_vcpu_is_be(vcpu)) {
>> +		switch (len) {
>> +		case 1:
>> +			return data & 0xff;
>> +		case 2:
>> +			return cpu_to_be16(data & 0xffff);
>> +		default:
>> +			return cpu_to_be32(data);
>> +		}
>> +	}
>> +
>> +	return data;		/* Leave LE untouched */
>> +}
>> +
>>  #endif /* __ARM_KVM_EMULATE_H__ */
>> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
>> index 0c25d94..54105f1b 100644
>> --- a/arch/arm/kvm/mmio.c
>> +++ b/arch/arm/kvm/mmio.c
>> @@ -23,6 +23,69 @@
>>  
>>  #include "trace.h"
>>  
>> +static void mmio_write_data(struct kvm_exit_mmio *mmio, unsigned long data)
>> +{
>> +	void *datap = NULL;
>> +	union {
>> +		u8	byte;
>> +		u16	hword;
>> +		u32	word;
>> +		u64	dword;
>> +	} tmp;
>> +
>> +	switch (mmio->len) {
>> +	case 1:
>> +		tmp.byte	= data;
>> +		datap		= &tmp.byte;
>> +		break;
>> +	case 2:
>> +		tmp.hword	= data;
>> +		datap		= &tmp.hword;
>> +		break;
>> +	case 4:
>> +		tmp.word	= data;
>> +		datap		= &tmp.word;
>> +		break;
>> +	case 8:
>> +		tmp.dword	= data;
>> +		datap		= &tmp.dword;
>> +		break;
>> +	}
>> +
>> +	memcpy(mmio->data, datap, mmio->len);
>> +}
>> +
>> +static unsigned long mmio_read_data(struct kvm_run *run)
>> +{
>> +	unsigned long data = 0;
>> +	unsigned int len = run->mmio.len;
>> +	union {
>> +		u16	hword;
>> +		u32	word;
>> +		u64	dword;
>> +	} tmp;
>> +
>> +	switch (len) {
>> +	case 1:
>> +		data = run->mmio.data[0];
>> +		break;
>> +	case 2:
>> +		memcpy(&tmp.hword, run->mmio.data, len);
>> +		data = tmp.hword;
>> +		break;
>> +	case 4:
>> +		memcpy(&tmp.word, run->mmio.data, len);
>> +		data = tmp.word;
>> +		break;
>> +	case 8:
>> +		memcpy(&tmp.dword, run->mmio.data, len);
>> +		data = tmp.dword;
>> +		break;
>> +	}
>> +
>> +	return data;
>> +}
>> +
> 
> don't we have similarly named functions for the vgic where we just
> assume accesses are always 32 bits?  Could we reuse?

Hmmm. The VGIC also deals with masks and stuff, and I'm not sure that's
worth the complexity. I'll rename this for the time being, and look at
unifying the two.

>>  /**
>>   * kvm_handle_mmio_return -- Handle MMIO loads after user space emulation
>>   * @vcpu: The VCPU pointer
>> @@ -33,28 +96,27 @@
>>   */
>>  int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>  {
>> -	unsigned long *dest;
>> +	unsigned long data;
>>  	unsigned int len;
>>  	int mask;
>>  
>>  	if (!run->mmio.is_write) {
>> -		dest = vcpu_reg(vcpu, vcpu->arch.mmio_decode.rt);
>> -		*dest = 0;
>> -
>>  		len = run->mmio.len;
>>  		if (len > sizeof(unsigned long))
>>  			return -EINVAL;
>>  
>> -		memcpy(dest, run->mmio.data, len);
>> -
>> -		trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
>> -				*((u64 *)run->mmio.data));
>> +		data = mmio_read_data(run);
>>  
>>  		if (vcpu->arch.mmio_decode.sign_extend &&
>>  		    len < sizeof(unsigned long)) {
>>  			mask = 1U << ((len * 8) - 1);
>> -			*dest = (*dest ^ mask) - mask;
>> +			data = (data ^ mask) - mask;
>>  		}
>> +
>> +		trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
>> +			       data);
>> +		data = vcpu_data_host_to_guest(vcpu, data, len);
>> +		*vcpu_reg(vcpu, vcpu->arch.mmio_decode.rt) = data;
>>  	}
>>  
>>  	return 0;
>> @@ -105,6 +167,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  		 phys_addr_t fault_ipa)
>>  {
>>  	struct kvm_exit_mmio mmio;
>> +	unsigned long data;
>>  	unsigned long rt;
>>  	int ret;
>>  
>> @@ -125,13 +188,15 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  	}
>>  
>>  	rt = vcpu->arch.mmio_decode.rt;
>> +	data = vcpu_data_guest_to_host(vcpu, *vcpu_reg(vcpu, rt), mmio.len);
>> +
>>  	trace_kvm_mmio((mmio.is_write) ? KVM_TRACE_MMIO_WRITE :
>>  					 KVM_TRACE_MMIO_READ_UNSATISFIED,
>>  			mmio.len, fault_ipa,
>> -			(mmio.is_write) ? *vcpu_reg(vcpu, rt) : 0);
>> +			(mmio.is_write) ? data : 0);
>>  
>>  	if (mmio.is_write)
>> -		memcpy(mmio.data, vcpu_reg(vcpu, rt), mmio.len);
>> +		mmio_write_data(&mmio, data);
>>  
>>  	if (vgic_handle_mmio(vcpu, run, &mmio))
>>  		return 1;
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index eec0738..3a7d058 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -177,4 +177,52 @@ static inline u8 kvm_vcpu_trap_get_fault(const struct kvm_vcpu *vcpu)
>>  	return kvm_vcpu_get_hsr(vcpu) & ESR_EL2_FSC_TYPE;
>>  }
>>  
>> +static inline bool kvm_vcpu_is_be(struct kvm_vcpu *vcpu)
>> +{
>> +	if (vcpu_mode_is_32bit(vcpu))
>> +		return !!(*vcpu_cpsr(vcpu) & COMPAT_PSR_E_BIT);
>> +
>> +	return !!(vcpu_sys_reg(vcpu, SCTLR_EL1) & (1 << 25));
> 
> do we have anywhere nice where we can stick a define for these bit
> fields?

Unfortunately not yet. But I can definitely see a need. Actually,
arch/arm has it all defined in cp15.h, which is quite nice.

I'll so something similar in a separate patch.

>> +}
>> +
>> +static inline unsigned long vcpu_data_guest_to_host(struct kvm_vcpu *vcpu,
>> +						    unsigned long data,
>> +						    unsigned int len)
>> +{
>> +	if (kvm_vcpu_is_be(vcpu)) {
>> +		switch (len) {
>> +		case 1:
>> +			return data & 0xff;
>> +		case 2:
>> +			return be16_to_cpu(data & 0xffff);
>> +		case 4:
>> +			return be32_to_cpu(data & ((1UL << 32) - 1));
> 
> why break the consistency here? wouldn't 0xffffffff be cleaner?
>

Fair enough.

>> +		default:
>> +			return be64_to_cpu(data);
>> +		}
>> +	}
>> +
>> +	return data;		/* Leave LE untouched */
>> +}
>> +
>> +static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>> +						    unsigned long data,
>> +						    unsigned int len)
>> +{
>> +	if (kvm_vcpu_is_be(vcpu)) {
>> +		switch (len) {
>> +		case 1:
>> +			return data & 0xff;
>> +		case 2:
>> +			return cpu_to_be16(data & 0xffff);
>> +		case 4:
>> +			return cpu_to_be32(data & ((1UL << 32) - 1));
>> +		default:
>> +			return cpu_to_be64(data);
>> +		}
>> +	}
>> +
>> +	return data;		/* Leave LE untouched */
>> +}
>> +
>>  #endif /* __ARM64_KVM_EMULATE_H__ */
>> -- 
>> 1.8.2.3
>>
>>
> 
> Functionally it still looks good:
> Acked-by: Christoffer Dall <[email-masked]>

Thanks. I'll do the above rework, and prepare an additional set of
patches to address some of the issues you noted.

Cheers,

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