On 07.12.20 21:13, Collin Walling wrote: > On 12/7/20 3:09 PM, Christian Borntraeger wrote: >> >> >> 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. >> > > Thanks. v5 with fix incoming. I think the test is actually fine and we should rather fix the kvm module to gracefully handle a userspace that starts up 2 or more guests.
