[PATCH 2/3] KVM: selftests: Consolidate boilerplate code in get_ucall()

[Huang, Shaoqin <shaoqin.huang@intel.com>]

On 6/18/2022 8:16 AM, Sean Christopherson wrote:
> Consolidate the actual copying of a ucall struct from guest=>host into
> the common get_ucall().  Return a host virtual address instead of a guest
> virtual address even though the addr_gva2hva() part could be moved to
> get_ucall() too.  Conceptually, get_ucall() is invoked from the host and
> should return a host virtual address (and returning NULL for "nothing to
> see here" is far superior to returning 0).

It seems the get_ucall() returns the uc->cmd, the ucall_arch_get_ucall() 
returns a host virtual address.

> 
> Use pointer shenanigans instead of an unnecessary bounce buffer when the
> caller of get_ucall() provides a valid pointer.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   .../selftests/kvm/include/ucall_common.h      |  8 ++------
>   .../testing/selftests/kvm/lib/aarch64/ucall.c | 15 +++------------
>   tools/testing/selftests/kvm/lib/riscv/ucall.c | 19 +++----------------
>   tools/testing/selftests/kvm/lib/s390x/ucall.c | 16 +++-------------
>   .../testing/selftests/kvm/lib/ucall_common.c  | 19 +++++++++++++++++++
>   .../testing/selftests/kvm/lib/x86_64/ucall.c  | 16 +++-------------
>   6 files changed, 33 insertions(+), 60 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/ucall_common.h b/tools/testing/selftests/kvm/include/ucall_common.h
> index c6a4fd7fe443..cb9b37282701 100644
> --- a/tools/testing/selftests/kvm/include/ucall_common.h
> +++ b/tools/testing/selftests/kvm/include/ucall_common.h
> @@ -26,9 +26,10 @@ struct ucall {
>   void ucall_arch_init(struct kvm_vm *vm, void *arg);
>   void ucall_arch_uninit(struct kvm_vm *vm);
>   void ucall_arch_do_ucall(vm_vaddr_t uc);
> -uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu);
>   
>   void ucall(uint64_t cmd, int nargs, ...);
> +uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
>   
>   static inline void ucall_init(struct kvm_vm *vm, void *arg)
>   {
> @@ -40,11 +41,6 @@ static inline void ucall_uninit(struct kvm_vm *vm)
>   	ucall_arch_uninit(vm);
>   }
>   
> -static inline uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> -{
> -	return ucall_arch_get_ucall(vcpu, uc);
> -}
> -
>   #define GUEST_SYNC_ARGS(stage, arg1, arg2, arg3, arg4)	\
>   				ucall(UCALL_SYNC, 6, "hello", stage, arg1, arg2, arg3, arg4)
>   #define GUEST_SYNC(stage)	ucall(UCALL_SYNC, 2, "hello", stage)
> diff --git a/tools/testing/selftests/kvm/lib/aarch64/ucall.c b/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> index 2de9fdd34159..9c124adbb560 100644
> --- a/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/aarch64/ucall.c
> @@ -75,13 +75,9 @@ void ucall_arch_do_ucall(vm_vaddr_t uc)
>   	*ucall_exit_mmio_addr = uc;
>   }
>   
> -uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_run *run = vcpu->run;
> -	struct ucall ucall = {};
> -
> -	if (uc)
> -		memset(uc, 0, sizeof(*uc));
>   
>   	if (run->exit_reason == KVM_EXIT_MMIO &&
>   	    run->mmio.phys_addr == (uint64_t)ucall_exit_mmio_addr) {
> @@ -90,12 +86,7 @@ uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
>   		TEST_ASSERT(run->mmio.is_write && run->mmio.len == 8,
>   			    "Unexpected ucall exit mmio address access");
>   		memcpy(&gva, run->mmio.data, sizeof(gva));
> -		memcpy(&ucall, addr_gva2hva(vcpu->vm, gva), sizeof(ucall));
> -
> -		vcpu_run_complete_io(vcpu);
> -		if (uc)
> -			memcpy(uc, &ucall, sizeof(ucall));
> +		return addr_gva2hva(vcpu->vm, gva);
>   	}
> -
> -	return ucall.cmd;
> +	return NULL;
>   }
> diff --git a/tools/testing/selftests/kvm/lib/riscv/ucall.c b/tools/testing/selftests/kvm/lib/riscv/ucall.c
> index b1598f418c1f..37e091d4366e 100644
> --- a/tools/testing/selftests/kvm/lib/riscv/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/riscv/ucall.c
> @@ -51,27 +51,15 @@ void ucall_arch_do_ucall(vm_vaddr_t uc)
>   		  uc, 0, 0, 0, 0, 0);
>   }
>   
> -uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_run *run = vcpu->run;
> -	struct ucall ucall = {};
> -
> -	if (uc)
> -		memset(uc, 0, sizeof(*uc));
>   
>   	if (run->exit_reason == KVM_EXIT_RISCV_SBI &&
>   	    run->riscv_sbi.extension_id == KVM_RISCV_SELFTESTS_SBI_EXT) {
>   		switch (run->riscv_sbi.function_id) {
>   		case KVM_RISCV_SELFTESTS_SBI_UCALL:
> -			memcpy(&ucall,
> -			       addr_gva2hva(vcpu->vm, run->riscv_sbi.args[0]),
> -			       sizeof(ucall));
> -
> -			vcpu_run_complete_io(vcpu);
> -			if (uc)
> -				memcpy(uc, &ucall, sizeof(ucall));
> -
> -			break;
> +			return addr_gva2hva(vcpu->vm, run->riscv_sbi.args[0]);
>   		case KVM_RISCV_SELFTESTS_SBI_UNEXP:
>   			vcpu_dump(stderr, vcpu, 2);
>   			TEST_ASSERT(0, "Unexpected trap taken by guest");
> @@ -80,6 +68,5 @@ uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
>   			break;
>   		}
>   	}
> -
> -	return ucall.cmd;
> +	return NULL;
>   }
> diff --git a/tools/testing/selftests/kvm/lib/s390x/ucall.c b/tools/testing/selftests/kvm/lib/s390x/ucall.c
> index 114cb4af295f..0f695a031d35 100644
> --- a/tools/testing/selftests/kvm/lib/s390x/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/s390x/ucall.c
> @@ -20,13 +20,9 @@ void ucall_arch_do_ucall(vm_vaddr_t uc)
>   	asm volatile ("diag 0,%0,0x501" : : "a"(uc) : "memory");
>   }
>   
> -uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_run *run = vcpu->run;
> -	struct ucall ucall = {};
> -
> -	if (uc)
> -		memset(uc, 0, sizeof(*uc));
>   
>   	if (run->exit_reason == KVM_EXIT_S390_SIEIC &&
>   	    run->s390_sieic.icptcode == 4 &&
> @@ -34,13 +30,7 @@ uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
>   	    (run->s390_sieic.ipb >> 16) == 0x501) {
>   		int reg = run->s390_sieic.ipa & 0xf;
>   
> -		memcpy(&ucall, addr_gva2hva(vcpu->vm, run->s.regs.gprs[reg]),
> -		       sizeof(ucall));
> -
> -		vcpu_run_complete_io(vcpu);
> -		if (uc)
> -			memcpy(uc, &ucall, sizeof(ucall));
> +		return addr_gva2hva(vcpu->vm, run->s.regs.gprs[reg]);
>   	}
> -
> -	return ucall.cmd;
> +	return NULL;
>   }
> diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c
> index 749ffdf23855..c488ed23d0dd 100644
> --- a/tools/testing/selftests/kvm/lib/ucall_common.c
> +++ b/tools/testing/selftests/kvm/lib/ucall_common.c
> @@ -18,3 +18,22 @@ void ucall(uint64_t cmd, int nargs, ...)
>   
>   	ucall_arch_do_ucall((vm_vaddr_t)&uc);
>   }
> +
> +uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> +{
> +	struct ucall ucall;
> +	void *addr;
> +
> +	if (!uc)
> +		uc = &ucall;
> +
> +	addr = ucall_arch_get_ucall(vcpu);
> +	if (addr) {
> +		memcpy(uc, addr, sizeof(*uc));
> +		vcpu_run_complete_io(vcpu);
> +	} else {
> +		memset(uc, 0, sizeof(*uc));
> +	}
> +
> +	return uc->cmd;
> +}
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/ucall.c b/tools/testing/selftests/kvm/lib/x86_64/ucall.c
> index 9f532dba1003..ec53a406f689 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/ucall.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/ucall.c
> @@ -22,25 +22,15 @@ void ucall_arch_do_ucall(vm_vaddr_t uc)
>   		: : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory");
>   }
>   
> -uint64_t ucall_arch_get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc)
> +void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_run *run = vcpu->run;
> -	struct ucall ucall = {};
> -
> -	if (uc)
> -		memset(uc, 0, sizeof(*uc));
>   
>   	if (run->exit_reason == KVM_EXIT_IO && run->io.port == UCALL_PIO_PORT) {
>   		struct kvm_regs regs;
>   
>   		vcpu_regs_get(vcpu, &regs);
> -		memcpy(&ucall, addr_gva2hva(vcpu->vm, (vm_vaddr_t)regs.rdi),
> -		       sizeof(ucall));
> -
> -		vcpu_run_complete_io(vcpu);
> -		if (uc)
> -			memcpy(uc, &ucall, sizeof(ucall));
> +		return addr_gva2hva(vcpu->vm, (vm_vaddr_t)regs.rdi);
>   	}
> -
> -	return ucall.cmd;
> +	return NULL;
>   }