Subject: Re: [PATCH v2] KVM: Optimize kvm_arch_vcpu_ioctl_run function

From: Vitaly Kuznetsov <[email-masked]>
Date: Thu, 16 Apr 2020 09:03:47 +0200

Tianjia Zhang <[email-masked]> writes:

> In earlier versions of kvm, 'kvm_run' is an independent structure
> and is not included in the vcpu structure. At present, 'kvm_run'
> is already included in the vcpu structure, so the parameter
> 'kvm_run' is redundant.
>
> This patch simplify the function definition, removes the extra
> 'kvm_run' parameter, and extract it from the 'kvm_vcpu' structure
> if necessary.
>
> Signed-off-by: Tianjia Zhang <[email-masked]>
> ---
>
> v2 change:
>   remove 'kvm_run' parameter and extract it from 'kvm_vcpu'
>
>  arch/mips/kvm/mips.c       |  3 ++-
>  arch/powerpc/kvm/powerpc.c |  3 ++-
>  arch/s390/kvm/kvm-s390.c   |  3 ++-
>  arch/x86/kvm/x86.c         | 11 ++++++-----
>  include/linux/kvm_host.h   |  2 +-
>  virt/kvm/arm/arm.c         |  6 +++---
>  virt/kvm/kvm_main.c        |  2 +-
>  7 files changed, 17 insertions(+), 13 deletions(-)
>
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index 8f05dd0a0f4e..ec24adf4857e 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -439,8 +439,9 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  	return -ENOIOCTLCMD;
>  }
>  
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *run = vcpu->run;
>  	int r = -EINTR;
>  
>  	vcpu_load(vcpu);
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index e15166b0a16d..7e24691e138a 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -1764,8 +1764,9 @@ int kvm_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu, struct kvm_one_reg *reg)
>  	return r;
>  }
>  
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *run = vcpu->run;
>  	int r;
>  
>  	vcpu_load(vcpu);
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 19a81024fe16..443af3ead739 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4333,8 +4333,9 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  		store_regs_fmt2(vcpu, kvm_run);
>  }
>  
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *kvm_run = vcpu->run;
>  	int rc;
>  
>  	if (kvm_run->immediate_exit)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3bf2ecafd027..a0338e86c90f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8707,8 +8707,9 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
>  	trace_kvm_fpu(0);
>  }
>  
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *kvm_run = vcpu->run;
>  	int r;
>  
>  	vcpu_load(vcpu);
> @@ -8726,18 +8727,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  		r = -EAGAIN;
>  		if (signal_pending(current)) {
>  			r = -EINTR;
> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
> +			kvm_run->exit_reason = KVM_EXIT_INTR;
>  			++vcpu->stat.signal_exits;
>  		}
>  		goto out;
>  	}
>  
> -	if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
> +	if (kvm_run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
>  		r = -EINVAL;
>  		goto out;
>  	}
>  
> -	if (vcpu->run->kvm_dirty_regs) {
> +	if (kvm_run->kvm_dirty_regs) {
>  		r = sync_regs(vcpu);
>  		if (r != 0)
>  			goto out;
> @@ -8767,7 +8768,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  
>  out:
>  	kvm_put_guest_fpu(vcpu);
> -	if (vcpu->run->kvm_valid_regs)
> +	if (kvm_run->kvm_valid_regs)
>  		store_regs(vcpu);
>  	post_kvm_run_save(vcpu);
>  	kvm_sigset_deactivate(vcpu);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6d58beb65454..1e17ef719595 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -866,7 +866,7 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
>  				    struct kvm_mp_state *mp_state);
>  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  					struct kvm_guest_debug *dbg);
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run);
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu);
>  
>  int kvm_arch_init(void *opaque);
>  void kvm_arch_exit(void);
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 48d0ec44ad77..f5390ac2165b 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -639,7 +639,6 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
>  /**
>   * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code
>   * @vcpu:	The VCPU pointer
> - * @run:	The kvm_run structure pointer used for userspace state exchange
>   *
>   * This function is called through the VCPU_RUN ioctl called from user space. It
>   * will execute VM code in a loop until the time slice for the process is used
> @@ -647,8 +646,9 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
>   * return with return value 0 and with the kvm_run structure filled in with the
>   * required data for the requested emulation.
>   */
> -int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *run = vcpu->run;
>  	int ret;
>  
>  	if (unlikely(!kvm_vcpu_initialized(vcpu)))
> @@ -659,7 +659,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		return ret;
>  
>  	if (run->exit_reason == KVM_EXIT_MMIO) {
> -		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
> +		ret = kvm_handle_mmio_return(vcpu, run);

I don't know much about ARM but this also seems redundant,
kvm_handle_mmio_return() is also able to extruct 'struct kvm_run' from'
'struct kvm_vcpu'. This likely deserves it's own patch though.

>  		if (ret)
>  			return ret;
>  	}
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 74bdb7bf3295..e18faea89146 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3135,7 +3135,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  				synchronize_rcu();
>  			put_pid(oldpid);
>  		}
> -		r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
> +		r = kvm_arch_vcpu_ioctl_run(vcpu);
>  		trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
>  		break;
>  	}

Looked at non-x86 arches just briefly but there seems to be no
controversy here, so

Reviewed-by: Vitaly Kuznetsov <[email-masked]>

-- 
Vitaly