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

["Lira, Victor M" <VictorM.Lira@xxxxxxx>]

On 4/14/2025 1:25 AM, Roger Pau Monné wrote:
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>
>
> > (XEN) [    7.943830] *** Building a PVH Dom0 ***
> > (XEN) [    7.955960] d0: identity mappings for IOMMU:
> > (XEN) [    7.965494]  [00000000a0, 00000000ff] RW
> > (XEN) [    7.974336]  [0000009bff, 0000009fff] RW
> > (XEN) [    7.983172]  [00000cabc9, 00000cc14c] RW
> > (XEN) [    7.992049]  [00000cc389, 00000cc389] RW
> > (XEN) [    8.000890]  [00000cc70a, 00000cd1fe] RW
> > (XEN) [    8.010065]  [00000ce000, 00000cffff] RW
> > (XEN) [    8.018904]  [00000fd000, 00000fd2ff] RW
> > (XEN) [    8.027745]  [00000fd304, 00000febff] RW
> > (XEN) [    8.036584]  [00000fec02, 00000fedff] RW
> > (XEN) [    8.045546]  [00000fee01, 00000fffff] RW
> > (XEN) [    8.054519]  [000080f340, 00008501ff] RW
> > (XEN) [    8.064135] 0000:02:00.0: not mapping BAR [fea00, fea03] invalid 
> > position
> > (XEN) [    8.078698] 0000:03:00.0: not mapping BAR [fe900, fe90f] invalid 
> > position
> > (XEN) [    8.093260] 0000:03:00.0: not mapping BAR [fe910, fe913] invalid 
> > position
> > (XEN) [    8.107815] 0000:04:00.0: not mapping BAR [fe700, fe77f] invalid 
> > position
> > (XEN) [    8.122376] 0000:04:00.3: not mapping BAR [fe500, fe5ff] invalid 
> > position
> > (XEN) [    8.136936] 0000:04:00.4: not mapping BAR [fe400, fe4ff] invalid 
> > position
> > (XEN) [    8.151498] 0000:05:00.0: not mapping BAR [fe801, fe801] invalid 
> > position
> > (XEN) [    8.166056] 0000:05:00.1: not mapping BAR [fe800, fe800] invalid 
> > position
> Note those messages don't imply that the BARs are not mapped in the
> dom0 p2m, for example here all the ranges listed as invalid positions
> are already mapped into the p2m and covered by the range:
>
> (XEN) [    8.027745]  [00000fd304, 00000febff] RW
>
> > [    6.378198] nvme nvme0: pci function 0000:02:00.0
> > (XEN) [   20.964789] d0v3 unable to fixup memory read from 0xfea0300c size 4: -1
> > [    6.387692] a(XEN) [   20.981772] d0v3 unable to fixup memory write to 
> > 0xfea03000 size 4: -1
> And here the address is somehow not populated in the p2m, despite
> being listed as an identity mapped region.  I think the real issue
> here is why this address is somehow unmapped from the p2m (or maybe
> not even added in the first place?).  Xen does identify it as a region
> that must be identity mapped.
>
> It's a fairly wild guess, but can you try if:
>
> https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=e118fc98e7ae652a188d227bd7ea22f132724150
>
> Makes a difference?  vPCI uses rangesets extensively, so the bug fixed
> above could in theory cause unmap operations to remove unintended
> regions, and could explain the symptoms you are seeing here.
>
> If that commit doesn't change behavior we would need to figure out why
> the identity ranges are either not properly mapped, or unexpectedly
> unmapped at a later point.
Hello,

Here is the output from Xen staging built including that commit. The 
behavior is as before.
Is there an existing way to see the physical to machine mappings? I 
didn't find anything in the Xen diagnostics.
I found the tool xen-mfndump but only PV is supported.

> / # xen-mfndump dump-p2m 0
> xc: error: Could not get domain address size (95 = Not supported): 
> Internal error
> Could not map domain 0 memory information
> / # xl list
> Name                                        ID   Mem VCPUs State   Time(s)
> Domain-0                                     0  4095     4 r-----     
> 348.8

Victor

Attachment: xen-staging-efi-overlap.log
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