> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 05 December 2017 17:19 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Julien Grall <julien.gr...@arm.com>; Andrew Cooper > <andrew.coop...@citrix.com>; xen-devel <xen- > de...@lists.xenproject.org> > Subject: RE: [PATCH] x86/HVM: don't retain emulated insn cache when > exiting back to guest > > >>> On 05.12.17 at 17:44, <paul.durr...@citrix.com> wrote: > >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> Sent: 05 December 2017 16:14 > >> --- a/xen/arch/x86/hvm/emulate.c > >> +++ b/xen/arch/x86/hvm/emulate.c > >> @@ -2109,20 +2109,22 @@ static int _hvm_emulate_one(struct hvm_e > >> > >> vio->mmio_retry = 0; > >> > >> - rc = x86_emulate(&hvmemul_ctxt->ctxt, ops); > >> - > >> - if ( rc == X86EMUL_OKAY && vio->mmio_retry ) > >> - rc = X86EMUL_RETRY; > >> - if ( rc != X86EMUL_RETRY ) > >> + switch ( rc = x86_emulate(&hvmemul_ctxt->ctxt, ops) ) > >> { > >> + case X86EMUL_OKAY: > >> + if ( vio->mmio_retry ) > >> + rc = X86EMUL_RETRY; > >> + /* fall through */ > >> + default: > >> vio->mmio_cache_count = 0; > >> vio->mmio_insn_bytes = 0; > >> - } > >> - else > >> - { > >> + break; > >> + > >> + 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; > > > > So, we have two distinct cases when X86EMUL_RETRY will be returned: the > > former when we do want to return to guest part way through a rep > operation, > > and another when an MMIO has been sent for external emulation and we > are > > expecting a completion. The code looks correct so... > > > > Reviewed-by: Paul Durrant <paul.durr...@citrix.com> > > Thanks. > > > ...but I wonder there should be two distinct return codes for these two > > cases. > > The question is - does any of the callers care about the difference. > I think the relevant information has been recorded in data structures > by the time we get here.
Technically, no I don't think the callers need to know but I've certainly got a bit tied in knots while trying to remember how this stuff is supposed to work so I was just hoping something could be done to make the 'don't return to guest because we need to retry mmio' and the 'return to guest even though want to retry a string operation' cases more obviously distinct. Paul > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
