Re: [PATCH] pvh: change epte_get_entry_emt() for pvh mem types

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Fri, 22 Nov 2013 12:05:03 +0000
"Jan Beulich" <JBeulich@suse.com> wrote:

> >>> On 22.11.13 at 11:52, George Dunlap <george.dunlap@eu.citrix.com>
> >>> wrote:
> > On 22/11/13 01:00, Mukesh Rathor wrote:
> >> For pvh guests, epte_get_entry_emt() is incorrectly returning WB
> >> for all mem types because of the following check:
> >>      if ( !v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT] )
> >> Skip the check for pvh guests.
> >>
> >> Also note, MTRR ranges are not maintained for pvh, and a solution
> >> is being contrived using PAT.
> >>
> >> Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
> >> ---
> >>   xen/arch/x86/hvm/mtrr.c |    7 ++++++-
> >>   1 files changed, 6 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c
> >> index 4ff1e55..5427e1c 100644
> >> --- a/xen/arch/x86/hvm/mtrr.c
> >> +++ b/xen/arch/x86/hvm/mtrr.c
> >> @@ -693,7 +693,8 @@ uint8_t epte_get_entry_emt(struct domain *d,
> >> unsigned 
> > long gfn, mfn_t mfn,
> >>            ((d->vcpu == NULL) || ((v = d->vcpu[0]) == NULL)) )
> >>           return MTRR_TYPE_WRBACK;
> >>   
> >> -    if ( !v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT] )
> >> +    if ( !is_pvh_vcpu(v) &&
> >> +         !v->domain->arch.hvm_domain.params[HVM_PARAM_IDENT_PT] )
> >>           return MTRR_TYPE_WRBACK;
> >>   
> >>       if ( !mfn_valid(mfn_x(mfn)) )
> >> @@ -717,6 +718,10 @@ uint8_t epte_get_entry_emt(struct domain *d,
> >> unsigned 
> > long gfn, mfn_t mfn,
> >>           return MTRR_TYPE_WRBACK;
> >>       }
> >>   
> >> +    /* MTRR ranges are not maintained for pvh. */
> >> +    if ( is_pvh_vcpu(v) )
> >> +        return MTRR_TYPE_WRBACK;
> >> +
> >>       gmtrr_mtype = get_mtrr_type(&v->arch.hvm_vcpu.mtrr, (gfn <<
> >> PAGE_SHIFT)); hmtrr_mtype = get_mtrr_type(&mtrr_state, (mfn_x(mfn)
> >> << PAGE_SHIFT)); return ((gmtrr_mtype <= hmtrr_mtype) ?
> >> gmtrr_mtype : hmtrr_mtype);
> > 
> > So this will bypass the host mtrr settings, and always return
> > WRBACK, even if in mtrr_state it was set to something lower.
> > Presumably that "min(host,guest)" was there for a reason.  Are you
> > sure it's safe to just ignore it?
> > 
> > This is why I suggested the following instead:
> > 
> > gmtrr_mtype = is_hvm_domain(v) ?
> >          get_mtrr_type(&v->arch.hvm_vcpu.mtrr, (gfn <<
> > PAGE_SHIFT)) : MTRR_TYPE_WRBACK;
> 
> Indeed, that's what we should use.

Sorry, totally my bad. For some reason I had concluded that hmtrr_mtype
was being set to UC. V2 patch on the way...

thanks
Mukesh