Subject: [PATCH] KVM: arm/arm64: avoid using kvm_run for in-kernel emulation

From: [email-masked] (Andre Przywara)
Date: Thu, 09 Apr 2015 16:55:45 +0100

Hej Christoffer,

On 09/04/15 14:30, Christoffer Dall wrote:
> On Sat, Mar 28, 2015 at 01:48:20AM +0000, Andre Przywara wrote:
>> Our in-kernel VGIC emulation still uses struct kvm_run briefly before
>> writing back the emulation result into the guest register. Using a
>> userspace mapped data structure within the kernel sounds dodgy, also
>> we do some extra copying at the moment at the end of the VGIC
>> emulation code.
>> Replace the usage of struct kvm_run in favour of passing separate
>> parameters into kvm_handle_mmio_return (and rename the function on
>> the way) to optimise the VGIC emulation. The real userland MMIO code
>> path does not change much.
>>
>> Signed-off-by: Andre Przywara <[email-masked]>
>> ---
>> Hi,
>>
>> this is an optimization of the VGIC code totally removing struct
>> kvm_run from the VGIC emulation. In my eyes it provides a nice
>> cleanup and is a logical consequence of the kvm_io_bus patches (on
>> which it goes on top). On the other hand it is optional and I didn't
>> want to merge it with the already quite large last patch 11.
>> Marc, I leave it up to you whether you take this as part of the
>> kvm_io_bus series or not.
>>
>> Cheers,
>> Andre.
>>
>>  arch/arm/include/asm/kvm_mmio.h   |    3 +-
>>  arch/arm/kvm/arm.c                |    6 ++--
>>  arch/arm/kvm/mmio.c               |   55 ++++++++++++++++++-------------------
>>  arch/arm64/include/asm/kvm_mmio.h |    3 +-
>>  virt/kvm/arm/vgic.c               |    8 ++----
>>  5 files changed, 37 insertions(+), 38 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_mmio.h b/arch/arm/include/asm/kvm_mmio.h
>> index d8e90c8..53461a6 100644
>> --- a/arch/arm/include/asm/kvm_mmio.h
>> +++ b/arch/arm/include/asm/kvm_mmio.h
>> @@ -28,7 +28,8 @@ struct kvm_decode {
>>  	bool sign_extend;
>>  };
>>  
>> -int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
>> +int kvm_writeback_mmio_data(struct kvm_vcpu *vcpu, unsigned int len,
>> +			    void *val, gpa_t phys_addr);
>>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  		 phys_addr_t fault_ipa);
>>  
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index e98370c..b837aef 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -506,8 +506,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>  	if (ret)
>>  		return ret;
>>  
>> -	if (run->exit_reason == KVM_EXIT_MMIO) {
>> -		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
>> +	if (run->exit_reason == KVM_EXIT_MMIO && !run->mmio.is_write) {
>> +		ret = kvm_writeback_mmio_data(vcpu, run->mmio.len,
>> +					      run->mmio.data,
>> +					      run->mmio.phys_addr);
>>  		if (ret)
>>  			return ret;
>>  	}
>> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
>> index 974b1c6..3c57f96 100644
>> --- a/arch/arm/kvm/mmio.c
>> +++ b/arch/arm/kvm/mmio.c
>> @@ -86,38 +86,36 @@ static unsigned long mmio_read_buf(char *buf, unsigned int len)
>>  }
>>  
>>  /**
>> - * kvm_handle_mmio_return -- Handle MMIO loads after user space emulation
>> - * @vcpu: The VCPU pointer
>> - * @run:  The VCPU run struct containing the mmio data
>> + * kvm_writeback_mmio_data -- Handle MMIO loads after user space emulation
>> + * @vcpu:	The VCPU pointer
>> + * @len:	The length in Bytes of the MMIO access
>> + * @data_ptr:	Pointer to the data to be written back into the guest
>> + * @phys_addr:	Physical address of the originating MMIO access
>>   *
>>   * This should only be called after returning from userspace for MMIO load
>> - * emulation.
>> + * emulation. phys_addr is only used for the tracepoint output.
>>   */
>> -int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>> +int kvm_writeback_mmio_data(struct kvm_vcpu *vcpu, unsigned int len,
>> +			    void *data_ptr, gpa_t phys_addr)
>>  {
>>  	unsigned long data;
>> -	unsigned int len;
>>  	int mask;
>>  
>> -	if (!run->mmio.is_write) {
>> -		len = run->mmio.len;
>> -		if (len > sizeof(unsigned long))
>> -			return -EINVAL;
>> +	if (len > sizeof(unsigned long))
>> +		return -EINVAL;
>>  
>> -		data = mmio_read_buf(run->mmio.data, len);
>> +	data = mmio_read_buf(data_ptr, len);
>>  
>> -		if (vcpu->arch.mmio_decode.sign_extend &&
>> -		    len < sizeof(unsigned long)) {
>> -			mask = 1U << ((len * 8) - 1);
>> -			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;
>> +	if (vcpu->arch.mmio_decode.sign_extend &&
>> +	    len < sizeof(unsigned long)) {
>> +		mask = 1U << ((len * 8) - 1);
>> +		data = (data ^ mask) - mask;
>>  	}
>>  
>> +	trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, phys_addr, data);
>> +	data = vcpu_data_host_to_guest(vcpu, data, len);
>> +	*vcpu_reg(vcpu, vcpu->arch.mmio_decode.rt) = data;
>> +
>>  	return 0;
>>  }
>>  
>> @@ -201,18 +199,19 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  				      data_buf);
>>  	}
>>  
>> -	/* Now prepare kvm_run for the potential return to userland. */
>> -	run->mmio.is_write	= is_write;
>> -	run->mmio.phys_addr	= fault_ipa;
>> -	run->mmio.len		= len;
>> -	memcpy(run->mmio.data, data_buf, len);
>> -
>>  	if (!ret) {
>>  		/* We handled the access successfully in the kernel. */
>> -		kvm_handle_mmio_return(vcpu, run);
>> +		if (!is_write)
>> +			kvm_writeback_mmio_data(vcpu, len, data_buf, fault_ipa);
>>  		return 1;
>>  	}
>>  
>> +	/* Now prepare the kvm_run structure for the return to userland. */
>> +	run->mmio.phys_addr	= fault_ipa;
>> +	run->mmio.len		= len;
>> +	run->mmio.is_write	= is_write;
>> +	memcpy(run->mmio.data, data_buf, len);
>>  	run->exit_reason	= KVM_EXIT_MMIO;
>> +
>>  	return 0;
>>  }
>> diff --git a/arch/arm64/include/asm/kvm_mmio.h b/arch/arm64/include/asm/kvm_mmio.h
>> index 889c908..3b83475 100644
>> --- a/arch/arm64/include/asm/kvm_mmio.h
>> +++ b/arch/arm64/include/asm/kvm_mmio.h
>> @@ -31,7 +31,8 @@ struct kvm_decode {
>>  	bool sign_extend;
>>  };
>>  
>> -int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
>> +int kvm_writeback_mmio_data(struct kvm_vcpu *vcpu, unsigned int len,
>> +			    void *val, gpa_t phys_addr);
>>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  		 phys_addr_t fault_ipa);
>>  
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index b70174e..4047fc0 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -803,7 +803,6 @@ static int vgic_handle_mmio_access(struct kvm_vcpu *vcpu,
>>  	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>>  	struct vgic_io_device *iodev = container_of(this,
>>  						    struct vgic_io_device, dev);
>> -	struct kvm_run *run = vcpu->run;
>>  	const struct vgic_io_range *range;
>>  	struct kvm_exit_mmio mmio;
>>  	bool updated_state;
>> @@ -832,12 +831,9 @@ static int vgic_handle_mmio_access(struct kvm_vcpu *vcpu,
>>  		updated_state = false;
>>  	}
>>  	spin_unlock(&dist->lock);
>> -	run->mmio.is_write	= is_write;
>> -	run->mmio.len		= len;
>> -	run->mmio.phys_addr	= addr;
>> -	memcpy(run->mmio.data, val, len);
>>  
>> -	kvm_handle_mmio_return(vcpu, run);
>> +	if (!is_write)
>> +		kvm_writeback_mmio_data(vcpu, len, val, addr);
> 
> why do we do a kvm_writeback_mmio_data() call here in addition to
> io_mem_abort() ?  Are we not doing this twice?  What am I missing?

You are missing: ... nothing, we are indeed doing it twice. This looks
like an oversight when converting from using a data buffer to a pointer.

So we can drop this here, and io_mem_abort() takes care (tested
quickly). Shall I add a comment or just remove those two lines?

Are you OK with the rest of the patch?

Cheers,
Andre.