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

[Sean Christopherson <seanjc@google.com>]

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).

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;
 }
-- 
2.37.0.rc0.104.g0611611a94-goog