Hi Anessh, On Tue, Apr 29, 2025 at 09:07:02AM +0530, Aneesh Kumar K.V wrote: > Alexandru Elisei <alexandru.elisei@xxxxxxx> writes: > > > Hi Aneesh, > > > > Is this to fix Will's report that the series breaks boot on x86? > > > > Yes. > > > On Mon, Apr 28, 2025 at 05:27:44PM +0530, Aneesh Kumar K.V (Arm) wrote: > >> When KVM_RUN fails with EINTR or EAGAIN, we should retry the ioctl > >> without checking kvm_run->exit_reason. These errors don't indicate a > >> valid VM exit, hence exit_reason may contain stale or undefined values. > > > > EAGAIN is not documented in Documentation/virt/kvm/api.rst. So I'm going to > > assume it's this code path that is causing the -EAGAIN return value [1]. > > > > IIUC, EAGAIN and EINTR are syscall return errno that indicates a system > call need to be retried. Documentation/virt/kvm/api.rst do mention that > exit_reason is value only with return value 0. > > __u32 exit_reason; > > When KVM_RUN has returned successfully (return value 0), this informs > application code why KVM_RUN has returned. Yeah, that makes sense. api.rst is a bit weird, because it doesn't document all of the error codes, and they are documented in different places, like -EFAULT which is under KVM_EXIT_MEMORY_FAULT, not under KVM_RUN. Thanks for the explanation! > > > > > If that's the case, how does retrying KVM_RUN solve the issue? Just trying to > > get to the bottom of it, because there's not much detail in the docs. > > > > [1] https://elixir.bootlin.com/linux/v6.15-rc3/source/arch/x86/kvm/x86.c#L11532 > > > > > > So in that code path vcpu will be in kvm_vcpu_block(vcpu) waiting for > the IPI. On IPI kvm_apic_accept_events() will return 0 after setting the > vcpu->arch.mp_state. Hence a KVM_RUN ioctl again will find the mp_state > correctly updated. I think that would be useful to have in the commit message. Thanks, Alex > > -aneesh
