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Subject: Re: [PATCH 7/7] KVM: MIPS: clean up redundant kvm_run parameters in
 assembly
To:     maobibo <maobibo@loongson.cn>, pbonzini@redhat.com,
        tsbogend@alpha.franken.de, paulus@ozlabs.org, mpe@ellerman.id.au,
        benh@kernel.crashing.org, borntraeger@de.ibm.com,
        frankja@linux.ibm.com, david@redhat.com, cohuck@redhat.com,
        heiko.carstens@de.ibm.com, gor@linux.ibm.com,
        sean.j.christopherson@intel.com, vkuznets@redhat.com,
        wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        hpa@zytor.com, maz@kernel.org, james.morse@arm.com,
        julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
        christoffer.dall@arm.com, peterx@redhat.com, thuth@redhat.com
Cc:     kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
        kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200419075106.16248-1-tianjia.zhang@linux.alibaba.com>
 <20200419075106.16248-8-tianjia.zhang@linux.alibaba.com>
 <0b110e7f-9d08-496e-158e-8c3ff7307423@loongson.cn>
From:   Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Message-ID: <793b2b58-a199-c067-aec7-b07c444a6091@linux.alibaba.com>
Date:   Mon, 20 Apr 2020 18:42:15 +0800
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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@linux.alibaba.com>
>> ---
>>   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);
>>   
>>