Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

>>> On 27.01.18 at 02:27, wrote: >> On 25/01/18 16:09, Andrew Cooper wrote: >> > On 25/01/18 15:57, Jan Beulich wrote: >> > > > > > >> > > For the record, the overwhelming majority of calls to >> > > __sync_local_execstate() being responsible for the behavior >> > > come

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

> On 25/01/18 16:09, Andrew Cooper wrote: > > On 25/01/18 15:57, Jan Beulich wrote: > > > > > > > > > For the record, the overwhelming majority of calls to > > > __sync_local_execstate() being responsible for the behavior > > > come from invalidate_interrupt(), which suggests to me that > > >

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Fri, 2018-01-26 at 02:43 -0700, Jan Beulich wrote: > > > > On 26.01.18 at 02:08, wrote: > > And in order to go and investigate this a bit further, Jan, what is > > it > > that you were doing when you saw what you described above? AFAIUI, > > that's booting an HVM guest,

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

>>> On 26.01.18 at 02:08, wrote: > On Thu, 2018-01-25 at 19:49 +0100, Dario Faggioli wrote: >> On Thu, 2018-01-25 at 16:09 +, Andrew Cooper wrote: >> > On 25/01/18 15:57, Jan Beulich wrote: >> > > >> > > For the record, the overwhelming majority of calls to >> > >

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Thu, 2018-01-25 at 19:49 +0100, Dario Faggioli wrote: > On Thu, 2018-01-25 at 16:09 +, Andrew Cooper wrote: > > On 25/01/18 15:57, Jan Beulich wrote: > > > > > > For the record, the overwhelming majority of calls to > > > __sync_local_execstate() being responsible for the behavior > > >

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Thu, 2018-01-25 at 16:09 +, Andrew Cooper wrote: > On 25/01/18 15:57, Jan Beulich wrote: > > > > > > > For the record, the overwhelming majority of calls to > > __sync_local_execstate() being responsible for the behavior > > come from invalidate_interrupt(), which suggests to me that > >

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On 25/01/18 16:31, Jan Beulich wrote: On 25.01.18 at 17:09, wrote: >> On 25/01/18 15:57, Jan Beulich wrote: >> On 24.01.18 at 14:12, wrote: @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu *next)

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

>>> On 25.01.18 at 17:09, wrote: > On 25/01/18 15:57, Jan Beulich wrote: > On 24.01.18 at 14:12, wrote: >>> @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu >>> *next) >>> } >>> >>>

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

CC'ing Dario with a working email address this time... On 25/01/18 16:09, Andrew Cooper wrote: > On 25/01/18 15:57, Jan Beulich wrote: > On 24.01.18 at 14:12, wrote: >>> @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu >>> *next) >>>

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On 25/01/18 15:57, Jan Beulich wrote: On 24.01.18 at 14:12, wrote: >> @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu >> *next) >> } >> >> ctxt_switch_levelling(next); >> + >> +if ( opt_ibpb &&

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

>>> On 24.01.18 at 14:12, wrote: > @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu > *next) > } > > ctxt_switch_levelling(next); > + > +if ( opt_ibpb && !is_idle_domain(nextd) ) Is the idle domain check here really

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Wed, Jan 24, 2018 at 02:31:20PM +, David Woodhouse wrote: > On Wed, 2018-01-24 at 13:49 +, Andrew Cooper wrote: > > On 24/01/18 13:34, Woodhouse, David wrote: > > > I am loath to suggest *more* tweakables, but given the IBPB cost is > > > there any merit in having a mode which does it

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Wed, 2018-01-24 at 13:49 +, Andrew Cooper wrote: > On 24/01/18 13:34, Woodhouse, David wrote: > > I am loath to suggest *more* tweakables, but given the IBPB cost is > > there any merit in having a mode which does it only if the *domain* is > > different, regardless of vcpu_id? > > This

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On 24/01/18 13:34, Woodhouse, David wrote: > On Wed, 2018-01-24 at 13:12 +, Andrew Cooper wrote: >> + * Squash the domid and vcpu id together for comparason > *comparison > >> + * efficiency.  We could in principle stash and compare the >> struct >> + *

Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

On Wed, 2018-01-24 at 13:12 +, Andrew Cooper wrote: > + * Squash the domid and vcpu id together for comparason *comparison > + * efficiency.  We could in principle stash and compare the > struct > + * vcpu pointer, but this risks a false alias if a domain

[Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

Issuing an IBPB command flushes the Branch Target Buffer, so that any poison left by one vcpu won't remain when beginning to execute the next. The cost of IBPB is substantial, and skipped on transition to idle, as Xen's idle code is robust already. All transitions into vcpu context are fully