Re: [Xen-devel] [PATCH RFC] x86/shadow: adjust cachability flags handling

[Tim Deegan <tim@xxxxxxx>]

At 14:49 +0000 on 05 Mar (1394027364), Jan Beulich wrote:
> For one, including _PAGE_PAT in the pass-through flags is valid only
> for L1 entries (otherwise _PAGE_PSE_PAT would need looking at). Looking
> around I _think_ that for page directories we'd always get a valid MFN
> passed in here, and hence I _think_ the assertion is correct.
> 
> And second we need to avoid or-ing guest PAT/PCD/PWT with ones coming
> from pat_type_2_pte_flags()/get_pat_flags(). An alternative to the
> pass_thru_flags check might be to use mfn_valid(target_mfn).
> 
> --- a/xen/arch/x86/mm/shadow/multi.c
> +++ b/xen/arch/x86/mm/shadow/multi.c
> @@ -580,7 +580,10 @@ _sh_propagate(struct vcpu *v, 
>      if ( guest_supports_nx(v) )
>          pass_thru_flags |= _PAGE_NX_BIT;
>      if ( !shadow_mode_refcounts(d) && !mfn_valid(target_mfn) )
> +    {
> +        ASSERT(level == 1);

Yes, this assertion is correct -- enforced by this block just above:

    if ( !mfn_valid(target_mfn)
         && !(level == 1 && (!shadow_mode_refcounts(d) 
                             || p2mt == p2m_mmio_direct)) )
    {
        ASSERT((ft == ft_prefetch));
        *sp = shadow_l1e_empty();
        goto done;
    }

>          pass_thru_flags |= _PAGE_PAT | _PAGE_PCD | _PAGE_PWT;
> +    }
>      sflags = gflags & pass_thru_flags;
>  
>      /*
> @@ -588,6 +591,7 @@ _sh_propagate(struct vcpu *v, 
>       * caching attributes in the shadows to match what was asked for.
>       */
>      if ( (level == 1) && is_hvm_domain(d) &&
> +         !(pass_thru_flags & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)) &&

I don't think this is necessary -- is_hvm_domain() implies
shadow_mode_refcounts(), so we won't have set these flags in
pass_thru_flags above.

If you want to make a change for clarity, I'd be happier with 
ASSERT(!(gflags & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT))) here.

Cheers,

Tim.

>           !is_xen_heap_mfn(mfn_x(target_mfn)) )
>      {
>          unsigned int type;
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel