Hi Thomas, On Thu, Apr 28, 2022 at 03:48:03PM +0200, Thomas Gleixner wrote: > On Wed, Apr 27 2022 at 19:35, Thomas Gleixner wrote: > > On Wed, Apr 27 2022 at 09:59, Salvatore Bonaccorso wrote: > > XEN guests do not use the common PCI mask/unmask machinery which would > > unmask the interrupt on request_irq(). > > > > So I assume that the following happens: > > > > Guest Hypervisor > > > > msix_capabilities_init() > > .... > > alloc_irq() > > xen_magic() -> alloc_msix_interrupt() > > request_irq() > > > > msix_mask_all() -> trap > > do_magic() > > request_irq() > > unmask() > > xen_magic() > > unmask_evtchn() -> do_more_magic() > > > > So I assume further that msix_mask_all() actually is able to mask the > > interrupts in the hardware (ctrl word of the vector table) despite the > > hypervisor having allocated and requested the interrupt already. > > > > Nothing in XEN_HVM handles PCI/MSI[-X] mask/unmask in the guest, so I > > really have to ask why XEN_HVM does not disable PCI/MSI[-X] masking like > > XEN_PV does. I can only assume the answer is voodoo... > > > > Maybe the XEN people have some more enlightened answers to that. > > So I was talking to Juergen about this and he agrees, that for the case > where a XEN HVM guest uses the PIRQ/Eventchannel mechanism PCI/MSI[-X] > masking should be disabled like it is done for XEN PV. > > Why the hypervisor grants the mask write is still mysterious, but I > leave that to the folks who can master the XEN voodoo. > > I'll send out a patch in minute. Thank you. We are having Noah Meyerhans now testing the patch and he will report back if it works (Cc'ed here now). Regards, Salvatore
