On 07.12.20 21:06, Collin Walling wrote: > On 12/7/20 2:32 PM, Christian Borntraeger wrote: >> On 07.12.20 16:41, Collin Walling wrote: >>> The DIAGNOSE 0x0318 instruction, unique to s390x, is a privileged call >>> that must be intercepted via SIE, handled in userspace, and the >>> information set by the instruction is communicated back to KVM. >>> >>> To test the instruction interception, an ad-hoc handler is defined which >>> simply has a VM execute the instruction and then userspace will extract >>> the necessary info. The handler is defined such that the instruction >>> invocation occurs only once. It is up to the caller to determine how the >>> info returned by this handler should be used. >>> >>> The diag318 info is communicated from userspace to KVM via a sync_regs >>> call. This is tested During a sync_regs test, where the diag318 info is >>> requested via the handler, then the info is stored in the appropriate >>> register in KVM via a sync registers call. >>> >>> If KVM does not support diag318, then the tests will print a message >>> stating that diag318 was skipped, and the asserts will simply test >>> against a value of 0. >>> >>> Signed-off-by: Collin Walling <walling@xxxxxxxxxxxxx> >> >> Interestingly enough, this testcase actually trigger a bug: >> While we gracefully handle this (no crash) >> debugfs: Directory 'kvm-200206' with parent 's390dbf' already present! >> is certainly not ideal.... >> > > Odd... I wonder what triggered this behavior? > > I run my tests with a simple command: > > make summary=0 TARGETS=kvm kselftest > > This must have something to do with spinning up another VM to get the > diag318 data. I think if I have the sync_regs test call the diag handler > first, and then have the sync regs create a VM, that might solve that > issue... Yes, the s390dbf code will try to create a file named kvm-%pid. With 2 VMs the 2nd one fails. Luckily the kvm will be created anyway and also the shutdown seems to be fine, still.... > > May I ask how you encountered this bug so I may replicate in on my end? I just did make TARGETS=kvm selftests and then the error is on dmesg.
