Messages in this thread | | | Subject | Re: [Intel-wired-lan] [PATCH] e1000e: prevent division by zero if TIMINCA is zero | From | Mark D Rustad <> | Date | Tue, 10 May 2016 22:59:47 -0500 |
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Jarod Wilson <jarod@redhat.com> wrote:
> On Fri, May 06, 2016 at 11:43:17PM +0000, Rustad, Mark D wrote: >> Denys Vlasenko <dvlasenk@redhat.com> wrote: >> >>> Users report that under VMWare, er32(TIMINCA) returns zero. >>> This causes division by zero at init time as follows: >>> >>> ==> incvalue = er32(TIMINCA) & E1000_TIMINCA_INCVALUE_MASK; >>> for (i = 0; i < E1000_MAX_82574_SYSTIM_REREADS; i++) { >>> /* latch SYSTIMH on read of SYSTIML */ >>> systim_next = (cycle_t)er32(SYSTIML); >>> systim_next |= (cycle_t)er32(SYSTIMH) << 32; >>> >>> time_delta = systim_next - systim; >>> temp = time_delta; >>> ====> rem = do_div(temp, incvalue); >>> >>> This change makes kernel survive this, and users report that >>> NIC does work after this change. >>> >>> Since on real hardware incvalue is never zero, this should not affect >>> real hardware use case. > ... >> I seem to recall that this was rejected before because it really is >> VMWare's >> bug and, if they fix it, any existing VMs that use this will just work. >> Changing the driver will only fix it for vms that install a new driver. I >> don't object to doing it, it just seems like not the most effective >> place to >> address the issue. > > You could also have people who never update VMWare, for whom a kernel > work-around would be better. I think it'd be best to address it both at > the driver level and the emulated hardware level, to improve things for > the most possible users. Those who update neither hypervisor or > kernel/driver, well, they reap what they sow.
That is a sound argument for doing both. I would expect that there are more frozen VM images than host environments, but I can certainly imagine that some choose to freeze their host. Of course if everything is frozen there is no point at all. :-)
I am on an extended vacation, and don't work on e1000e anyway, so I will quit my kibitzing here.
-- Mark Rustad, MRustad@gmail.com [unhandled content-type:application/pgp-signature] | |