Re: [RFC] xen/x86: allow overlaps with non-RAM regions

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Apr 24, 2025 at 12:15:17PM +0200, Marek Marczykowski-Górecki wrote:
> On Thu, Apr 24, 2025 at 09:59:00AM +0200, Roger Pau Monné wrote:
> > On Wed, Apr 23, 2025 at 04:51:16PM -0700, Lira, Victor M wrote:
> > > [    4.570354] Intel(R) 2.5G Ethernet Linux Driver
> > > 
> > > [    4.579535] Copyright(c) 2018 Intel Corporation.
> > > 
> > > [    4.588898] sky2: driver version 1.30
> > > 
> > > (XEN) [   21.644361] d0v3 unable to fixup memory read from 0xfe91000c 
> > > size 4: -1
> > 
> > This fault is unexpected, according to the identity mappings done at
> > domain build time:
> > 
> > d0: identity mappings for IOMMU:
> >  [00000000a0, 00000000ff] RW
> >  [0000009bff, 0000009fff] RW
> >  [00000cabc9, 00000cc14c] RW
> >  [00000cc389, 00000cc389] RW
> >  [00000cc70a, 00000cd1fe] RW
> >  [00000ce000, 00000cffff] RW
> >  [00000fd000, 00000fd2ff] RW
> > 
> > The page at 0xfe910 should be covered by the last range above.  I
> > think we have a bug somewhere that unexpectedly unmaps that address.
> 
> You sure? 0xfe910 is outside of [00000fd000, 00000fd2ff].

Oh, did and off-by-one when copying, it should have been:

d0: identity mappings for IOMMU:
 [00000000a0, 00000000ff] RW
 [0000009bff, 0000009fff] RW
 [00000cabc9, 00000cc14c] RW
 [00000cc389, 00000cc389] RW
 [00000cc70a, 00000cd1fe] RW
 [00000ce000, 00000cffff] RW
 [00000fd000, 00000fd2ff] RW
 [00000fd304, 00000febff] RW

Where 0xfe910 is covered by the last range.

Regards, Roger.