> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 20 April 2018 13:34 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Andrew Cooper <andrew.coop...@citrix.com>; xen-devel <xen- > de...@lists.xenproject.org> > Subject: another state machine issue? (was: [PATCH] x86emul: adjust > handling of AVX2 gathers) > > >>> On 20.04.18 at 11:25, <jbeul...@suse.com> wrote: > > @@ -7692,12 +7693,23 @@ x86_emulate( > > ea.mem.off + (idx << state->sib_scale), > > (void *)mmvalp + i * op_bytes, op_bytes, > > ctxt); > > if ( rc != X86EMUL_OKAY ) > > + { > > + /* > > + * If we've made any progress and the access did not > > fault, > > + * force a retry instead. This is for example > > necessary to > > + * cope with the limited capacity of HVM's MMIO cache. > > + */ > > + if ( rc != X86EMUL_EXCEPTION && done ) > > + rc = X86EMUL_RETRY; > > break; > > + } > > > > #ifdef __XEN__ > > if ( i + 1 < n && local_events_need_delivery() ) > > rc = X86EMUL_RETRY; > > #endif > > I've just noticed that these two as well as any other current or future > X86EMUL_RETRY returns (at least ones directly from the emulator) are > in conflict with _hvm_emulate_one() having > > case X86EMUL_RETRY: > BUILD_BUG_ON(sizeof(vio->mmio_insn) < sizeof(hvmemul_ctxt- > >insn_buf)); > vio->mmio_insn_bytes = hvmemul_ctxt->insn_buf_bytes; > memcpy(vio->mmio_insn, hvmemul_ctxt->insn_buf, vio- > >mmio_insn_bytes); > break; > > when processing the result of x86_emulate(). I think we need to distinguish > here whether we are going to return to guest context (in which case we > need to discard all cached data, as done a few lines above) or whether > we're going to sleep. When exiting to guest, the guest may take an interrupt > before resuming the instruction we've been emulating, and if the interrupt > handler incurs emulation, we'd wrongly use the cached insn. If I'm not > mistaken, simply keying this off of hvm_vcpu_io_need_completion()'s result > should do. >
Well, as we know, things may go badly wrong if hvm_vcpu_io_need_completion() is true and we don't re-emulate same instruction so this sounds plausible. Paul > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
