On Sat, Jan 07, 2017 at 07:23:14AM +0000, Long Li wrote: > > -----Original Message----- > > From: Greg KH [mailto:g...@kroah.com] > > Sent: Wednesday, January 04, 2017 11:48 PM > > To: Long Li <lon...@microsoft.com> > > Cc: KY Srinivasan <k...@microsoft.com>; Haiyang Zhang > > <haiya...@microsoft.com>; de...@linuxdriverproject.org; linux- > > ker...@vger.kernel.org > > Subject: Re: [PATCH v2] hv: retry infinitely on hypercall transient failures > > > > On Wed, Jan 04, 2017 at 06:12:20PM -0800, Long Li wrote: > > > From: Long Li <lon...@microsoft.com> > > > > > > Hyper-v host guarantees that a hypercall will finish in reasonable time. > > > Retry infinitely on transient failures to avoid returning error to upper > > > layer. > > > > Again, never retry "forever", always have a way out, otherwise you will > > crash. > > > > And again, why are you making this change? What problem does it solve? > > The problem it tries to solve is that in this code we are returning > error prematurely on transient failures. The hypercall is used mostly > in channel establishment. If we return a transient failure, the VM may > not boot or not useful after boot due to some devices missing. > > Another approach is to increase the number of retries. But we don't > know how many retries is safe, and Windows host side expects the guest > retry infinitely and not return error on transient failures.
That implies a lot of trust in the host side, don't you think? Worse case, make the delay a minute or so, but give the system a way out incase there's a bug in the host. As there will be bugs in the host, just like there are bugs in the client :) thanks, greg k-h
