On Wed, Aug 07, 2024 at 02:29:31PM GMT, Andrew Jones wrote: > On Wed, Aug 07, 2024 at 01:36:33PM GMT, Andrew Jones wrote: > ... > > I just tried 32-bit KVM and see that the DBCN write test fails the > > 'write success' test. That may be a KVM bug. > > > > We can blame both KVM and kvmtool. > > KVM sets sbiret.error to a0 and sbiret.value to a1 before exiting to > userspace[1]. I think that comes from thinking about how a real ecall > would set them. However, as this isn't an ecall, they should get set > directly by userspace, not through registers. Also, we should initialize > them to some known value before calling userspace, and zero is probably > the best choice. Thinking about this some more and discussing it with Anup, the best choice for sbiret.error is to initialize it to SBI_ERR_NOT_SUPPORTED. Doing that won't allow the test to pass with old kvmtool, but that's OK. I'll send a KVM patch for that and the kvmtool patch. Thanks, drew > > kvmtool neglects to set sbiret.error to SBI_SUCCESS on a successful write. > QEMU does set it, so this failure shouldn't happen with QEMU, but I > haven't tried it. > > Patching both KVM and kvmtool is best, as it would allow the test to pass > when running new KVM with old kvmtool and when running old KVM with new > kvmtool. > > [1] arch/riscv/kvm/vcpu_sbi.c:130 > > Thanks, > drew > > -- > kvm-riscv mailing list > kvm-riscv@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/kvm-riscv
