Re: [PATCH 7/7] KVM: MIPS: clean up redundant kvm_run parameters in assembly

[maobibo]

On 04/19/2020 03:51 PM, Tianjia Zhang wrote:
> In the current kvm version, 'kvm_run' has been included in the 'kvm_vcpu'
> structure. Earlier than historical reasons, many kvm-related function
> parameters retain the 'kvm_run' and 'kvm_vcpu' parameters at the same time.
> This patch does a unified cleanup of these remaining redundant parameters.
> 
> Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> ---
>  arch/mips/include/asm/kvm_host.h |  4 ++--
>  arch/mips/kvm/entry.c            | 15 +++++----------
>  arch/mips/kvm/mips.c             |  3 ++-
>  arch/mips/kvm/trap_emul.c        |  2 +-
>  arch/mips/kvm/vz.c               |  2 +-
>  5 files changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> index 971439297cea..db915c55166d 100644
> --- a/arch/mips/include/asm/kvm_host.h
> +++ b/arch/mips/include/asm/kvm_host.h
> @@ -310,7 +310,7 @@ struct kvm_mmu_memory_cache {
>  #define KVM_MIPS_GUEST_TLB_SIZE	64
>  struct kvm_vcpu_arch {
>  	void *guest_ebase;
> -	int (*vcpu_run)(struct kvm_run *run, struct kvm_vcpu *vcpu);
> +	int (*vcpu_run)(struct kvm_vcpu *vcpu);
>  
>  	/* Host registers preserved across guest mode execution */
>  	unsigned long host_stack;
> @@ -821,7 +821,7 @@ int kvm_mips_emulation_init(struct kvm_mips_callbacks **install_callbacks);
>  /* Debug: dump vcpu state */
>  int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu);
>  
> -extern int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu);
> +extern int kvm_mips_handle_exit(struct kvm_vcpu *vcpu);
>  
>  /* Building of entry/exception code */
>  int kvm_mips_entry_setup(void);
> diff --git a/arch/mips/kvm/entry.c b/arch/mips/kvm/entry.c
> index 16e1c93b484f..e3f29af3b6cd 100644
> --- a/arch/mips/kvm/entry.c
> +++ b/arch/mips/kvm/entry.c
> @@ -204,7 +204,7 @@ static inline void build_set_exc_base(u32 **p, unsigned int reg)
>   * Assemble the start of the vcpu_run function to run a guest VCPU. The function
>   * conforms to the following prototype:
>   *
> - * int vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu);
> + * int vcpu_run(struct kvm_vcpu *vcpu);
>   *
>   * The exit from the guest and return to the caller is handled by the code
>   * generated by kvm_mips_build_ret_to_host().
> @@ -217,8 +217,7 @@ void *kvm_mips_build_vcpu_run(void *addr)
>  	unsigned int i;
>  
>  	/*
> -	 * A0: run
> -	 * A1: vcpu
> +	 * A0: vcpu
>  	 */
>  
>  	/* k0/k1 not being used in host kernel context */
> @@ -237,10 +236,10 @@ void *kvm_mips_build_vcpu_run(void *addr)
>  	kvm_mips_build_save_scratch(&p, V1, K1);
>  
>  	/* VCPU scratch register has pointer to vcpu */
> -	UASM_i_MTC0(&p, A1, scratch_vcpu[0], scratch_vcpu[1]);
> +	UASM_i_MTC0(&p, A0, scratch_vcpu[0], scratch_vcpu[1]);
>  
>  	/* Offset into vcpu->arch */
> -	UASM_i_ADDIU(&p, K1, A1, offsetof(struct kvm_vcpu, arch));
> +	UASM_i_ADDIU(&p, K1, A0, offsetof(struct kvm_vcpu, arch));
>  
>  	/*
>  	 * Save the host stack to VCPU, used for exception processing
> @@ -628,10 +627,7 @@ void *kvm_mips_build_exit(void *addr)
>  	/* Now that context has been saved, we can use other registers */
>  
>  	/* Restore vcpu */
> -	UASM_i_MFC0(&p, S1, scratch_vcpu[0], scratch_vcpu[1]);
> -
> -	/* Restore run (vcpu->run) */
> -	UASM_i_LW(&p, S0, offsetof(struct kvm_vcpu, run), S1);
> +	UASM_i_MFC0(&p, S0, scratch_vcpu[0], scratch_vcpu[1]);
>  
>  	/*
>  	 * Save Host level EPC, BadVaddr and Cause to VCPU, useful to process
> @@ -793,7 +789,6 @@ void *kvm_mips_build_exit(void *addr)
>  	 * with this in the kernel
>  	 */
>  	uasm_i_move(&p, A0, S0);
> -	uasm_i_move(&p, A1, S1);
>  	UASM_i_LA(&p, T9, (unsigned long)kvm_mips_handle_exit);
>  	uasm_i_jalr(&p, RA, T9);
>  	 UASM_i_ADDIU(&p, SP, SP, -CALLFRAME_SIZ);

I suggest keeping asm code untouched, the change for c code is much easier to understand, however I do not see obvious advantage to remove one redundant function parameter :) 


regards
bibo,mao


> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index 9710477a9827..32850470c037 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -1186,8 +1186,9 @@ static void kvm_mips_set_c0_status(void)
>  /*
>   * Return value is in the form (errcode<<2 | RESUME_FLAG_HOST | RESUME_FLAG_NV)
>   */
> -int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
> +int kvm_mips_handle_exit(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_run *run = vcpu->run;
>  	u32 cause = vcpu->arch.host_cp0_cause;
>  	u32 exccode = (cause >> CAUSEB_EXCCODE) & 0x1f;
>  	u32 __user *opc = (u32 __user *) vcpu->arch.pc;
> diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
> index d822f3aee3dc..04c864cc356a 100644
> --- a/arch/mips/kvm/trap_emul.c
> +++ b/arch/mips/kvm/trap_emul.c
> @@ -1238,7 +1238,7 @@ static int kvm_trap_emul_vcpu_run(struct kvm_vcpu *vcpu)
>  	 */
>  	kvm_mips_suspend_mm(cpu);
>  
> -	r = vcpu->arch.vcpu_run(vcpu->run, vcpu);
> +	r = vcpu->arch.vcpu_run(vcpu);
>  
>  	/* We may have migrated while handling guest exits */
>  	cpu = smp_processor_id();
> diff --git a/arch/mips/kvm/vz.c b/arch/mips/kvm/vz.c
> index 94f1d23828e3..c5878fa0636d 100644
> --- a/arch/mips/kvm/vz.c
> +++ b/arch/mips/kvm/vz.c
> @@ -3152,7 +3152,7 @@ static int kvm_vz_vcpu_run(struct kvm_vcpu *vcpu)
>  	kvm_vz_vcpu_load_tlb(vcpu, cpu);
>  	kvm_vz_vcpu_load_wired(vcpu);
>  
> -	r = vcpu->arch.vcpu_run(vcpu->run, vcpu);
> +	r = vcpu->arch.vcpu_run(vcpu);
>  
>  	kvm_vz_vcpu_save_wired(vcpu);
>  
>