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

[Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>]

On 2020/4/20 18:32, maobibo wrote:
> 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

This is acceptable, asm code is an independent patch, is to provide 
convenience for this operation.

> > 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);
> >