> -----Original Message----- > From: Jan Beulich <jbeul...@suse.com> > Sent: 03 March 2020 14:21 > To: Durrant, Paul <pdurr...@amazon.co.uk> > Cc: xen-devel@lists.xenproject.org; Andrew Cooper > <andrew.coop...@citrix.com>; Roger Pau Monné <roger....@citrix.com>; Wei > Liu <w...@xen.org>; Paul Durrant <p...@xen.org> > Subject: RE: [EXTERNAL][Xen-devel] [PATCH v5 1/4] x86/HVM: cancel > emulation when register state got altered > > On 03.03.2020 14:16, Durrant, Paul wrote: > >> -----Original Message----- > >> From: Xen-devel <xen-devel-boun...@lists.xenproject.org> On Behalf Of > Jan > >> Beulich > >> Sent: 03 March 2020 10:17 > >> To: xen-devel@lists.xenproject.org > >> Cc: Andrew Cooper <andrew.coop...@citrix.com>; Roger Pau Monné > >> <roger....@citrix.com>; Wei Liu <w...@xen.org>; Paul Durrant > <p...@xen.org> > >> Subject: [EXTERNAL][Xen-devel] [PATCH v5 1/4] x86/HVM: cancel emulation > >> when register state got altered > >> > >> Re-execution (after having received data from a device model) relies on > >> the same register state still being in place as it was when the request > >> was first sent to the device model. Therefore vCPU state changes > >> effected by remote sources need to result in no attempt of re- > execution. > >> Instead the returned data is to simply be ignored. > >> > >> Note that any such asynchronous state changes happen with the vCPU at > >> least paused (potentially down and/or not marked ->is_initialised), so > >> there's no issue with fiddling with register state behind the actively > >> running emulator's back. Hence the new function doesn't need to > >> synchronize with the core emulation logic. > >> > >> Suggested-by: Andrew Cooper <andrew.coop...@citrix.com> > >> Signed-off-by: Jan Beulich <jbeul...@suse.com> > > > > Need we be concerned with any page-split I/O here? That may manifest as > > two separate emulations and AFAICT it would be possible for only the > > second part to be aborted by this change. > > I'm not sure whether e.g. INIT is recognized only on insn boundaries. > I.e. this may not be that different from real hardware behavior. _If_ > we were to take care of this, how would you envision undoing the > first part of such an access, most notably when the access has side > effects?
I wasn't thinking of undoing... I was more thinking that vcpu_pause() ought to defer until an in-progress emulation has fully completed. Paul > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel