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

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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@xxxxxxxxxx>
---
  .../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;
  }
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