[PATCH kvmtool 1/5] arm64: Do not abort on register-dump failures

[Fuad Tabba <fuad.tabba@linux.dev>]

kvm_cpu__show_registers() and kvm_cpu__show_code() read the vCPU's core
registers with KVM_GET_ONE_REG, and die() if the ioctl fails. Both are
diagnostics. They run from the KVM_EXIT_DEBUG case in kvm_cpu__start(),
from the "lkvm debug -d" dump path in handle_sigusr1(), and from the
panic dump in kvm_cpu_thread().

Once a protected vCPU has run, its registers belong to the guest and
KVM_GET_ONE_REG returns -EPERM. Dying on that turns a diagnostic into a
VMM abort.

Report that the register state is unavailable, with the errno, and
return instead of dying.

Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arm64/kvm-cpu.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/arm64/kvm-cpu.c b/arm64/kvm-cpu.c
index 3aa7684..c58d61f 100644
--- a/arm64/kvm-cpu.c
+++ b/arm64/kvm-cpu.c
@@ -476,15 +476,19 @@ void kvm_cpu__show_code(struct kvm_cpu *vcpu)
 
 	dprintf(debug_fd, "\n*pc:\n");
 	reg.id = ARM64_CORE_REG(regs.pc);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (show_code @ PC)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (pc): %s", strerror(errno));
+		return;
+	}
 
 	kvm__dump_mem(vcpu->kvm, data, 32, debug_fd);
 
 	dprintf(debug_fd, "\n*lr:\n");
 	reg.id = ARM64_CORE_REG(regs.regs[30]);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (show_code @ LR)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (lr): %s", strerror(errno));
+		return;
+	}
 
 	kvm__dump_mem(vcpu->kvm, data, 32, debug_fd);
 }
@@ -499,23 +503,31 @@ void kvm_cpu__show_registers(struct kvm_cpu *vcpu)
 	dprintf(debug_fd, "\n Registers:\n");
 
 	reg.id		= ARM64_CORE_REG(regs.pc);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (pc)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (pc): %s", strerror(errno));
+		return;
+	}
 	dprintf(debug_fd, " PC:    0x%lx\n", data);
 
 	reg.id		= ARM64_CORE_REG(regs.pstate);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (pstate)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (pstate): %s", strerror(errno));
+		return;
+	}
 	dprintf(debug_fd, " PSTATE:    0x%lx\n", data);
 
 	reg.id		= ARM64_CORE_REG(sp_el1);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (sp_el1)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (sp_el1): %s", strerror(errno));
+		return;
+	}
 	dprintf(debug_fd, " SP_EL1:    0x%lx\n", data);
 
 	reg.id		= ARM64_CORE_REG(regs.regs[30]);
-	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
-		die("KVM_GET_ONE_REG failed (lr)");
+	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
+		pr_err("register state unavailable (lr): %s", strerror(errno));
+		return;
+	}
 	dprintf(debug_fd, " LR:    0x%lx\n", data);
 }
 
-- 
2.39.5