Re: port-xen/52016: Mismatch between mem_clusters and pmap_enter bounds check

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR port-xen/52016; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: port-xen-maintainer%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
        netbsd-bugs%netbsd.org@localhost, coypu%sdf.org@localhost
Subject: Re: port-xen/52016: Mismatch between mem_clusters and pmap_enter
 bounds check
Date: Wed, 1 Mar 2017 13:12:23 +0100

 On Wed, Mar 01, 2017 at 12:05:00PM +0000, coypu%SDF.ORG@localhost wrote:
 > The following reply was made to PR port-xen/52016; it has been noted by GNATS.
 > 
 > From: coypu%SDF.ORG@localhost
 > To: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
 > Cc: gnats-bugs%NetBSD.org@localhost
 > Subject: Re: port-xen/52016: Mismatch between mem_clusters and pmap_enter
 >  bounds check
 > Date: Wed, 1 Mar 2017 12:03:10 +0000
 > 
 >  From a really far from sufficiently thorough look at linux, it looks
 >  like it might be equivalent to putting stuff that is directly accessed
 >  within [pmap_pa_start,pmap_pa_end) and having magic to map it to
 >  "identity".
 
 But then you may have holes in between pmap_pa_start and pmap_pa_end.
 I think we should keep pmap_pa* for pseudo-physical addresses only,
 and add something else for machine addresses - if we have a way to
 know mappable machine addresses.
 One problem is that you may want to map machine addresses which falls into
 the pseudo-physical address range via /dev/mem. In this case you don't have
 a way to know which kind of address this is.
 
 Using /dev/mem for both kind of addresses is bogus.
 
 >  
 >  And we can decide for domU that some stuff points to a dummy page and
 >  so HYPERVISOR_mmu_update doesn't fail for it.
 
 a domU doesn't need to map machine addresses via /dev/mem (and the hypervisor
 won't allow it).
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --