Re: 15 & 14: ram_attach vs. its using regions_to_avail vs. "bus_alloc_resource" can lead to: panic("ram_attach: resource %d failed to attach", rid)

On Sat, 30 Sept 2023 at 08:47, Mark Millard <marklmi@yahoo.com> wrote:

> ram_attach is based on regions_to_avail but that is a problem for
> its later bus_alloc_resource use --and that can lead to:
>
> panic("ram_attach: resource %d failed to attach", rid);
>
> Unfortunately, the known example is use of EDK2 on RPi4B
> class systems, not what is considered the supported way.
> The panic happens for main [so: 15] and will happen once
> the cortex-a72 handling in 14.0-* is in a build fixed by:
>
>     • git: 906bcc44641d - releng/14.0 - arm64: Fix errata workarounds that
> depend on smccc Andrew Turner
>
> The lack of the fix leads to an earlier panic as stands.
>
>
> sys/kern/subr_physmem.c 's regions_to_avail is based on ignoring
> phys_avail and using only hwregions and exregions. In other words,
> in part:
>
>  * Initially dump_avail and phys_avail are identical.  Boot time memory
>  * allocations remove extents from phys_avail that may still be included
>  * in dumps.
>
> This means that early, dedicated memory allocations are treated
> as available for general use by regions_to_avail . The distinction
> is visible in the  boot -v output in that:
>
> real memory  = 3138154496 (2992 MB)
> Physical memory chunk(s):
> 0x00000000200000 - 0x0000002b7fffff, 727711744 bytes (177664 pages)
> 0x0000002ce3a000 - 0x0000003385ffff, 111304704 bytes (27174 pages)
> 0x000000338c0000 - 0x000000338c6fff, 28672 bytes (7 pages)
> 0x00000033a30000 - 0x00000036efffff, 55377920 bytes (13520 pages)
> 0x000000372e0000 - 0x0000003b2fffff, 67239936 bytes (16416 pages)
> 0x00000040000000 - 0x000000bb3dcfff, 2067648512 bytes (504797 pages)
> avail memory = 3027378176 (2887 MB)
>
> does not list the wider:
>
> 0x00000040000000 - 0x000000bfffffff
>
> because of phys_avail . But the earlier dump based on hwregions and
> exregions shows:
>
> Physical memory chunk(s):
>   0x001d0000 - 0x001effff,     0 MB (     32 pages)
>   0x00200000 - 0x338c6fff,   822 MB ( 210631 pages)
>   0x33920000 - 0x3b2fffff,   121 MB (  31200 pages)
>   0x40000000 - 0xbfffffff,  2048 MB ( 524288 pages)
> Excluded memory regions:
>   0x001d0000 - 0x001effff,     0 MB (     32 pages) NoAlloc
>   0x2b800000 - 0x2ce39fff,    22 MB (   5690 pages) NoAlloc
>   0x33860000 - 0x338bffff,     0 MB (     96 pages) NoAlloc
>   0x33920000 - 0x33a2ffff,     1 MB (    272 pages) NoAlloc
>   0x36f00000 - 0x372dffff,     3 MB (    992 pages) NoAlloc
>
> which indicates:
>
>   0x40000000 - 0xbfffffff
>
> is available as far as it is concerned.
>
> (Note some code works/displays in terms of: 0x40000000 - 0xc0000000
> instead.)
>
> For aarch64 , sys/arm64/arm64/nexus.c has a nexus_alloc_resource
> that is used as bus_alloc_resource . It ends up rejecting the
> RPi4B boot via using the result of the call in ram_attach:
>
>                 if (bus_alloc_resource(dev, SYS_RES_MEMORY, &rid, start,
> end,
>                     end - start, 0) == NULL)
>                         panic("ram_attach: resource %d failed to attach",
> rid);
>
> as shown by the just-prior start/end pair sequence messages:
>
> ram0: reserving memory region:   200000-2b800000
> ram0: reserving memory region:   2ce3a000-33860000
> ram0: reserving memory region:   338c0000-338c7000
> ram0: reserving memory region:   33a30000-36f00000
> ram0: reserving memory region:   372e0000-3b300000
> ram0: reserving memory region:   40000000-c0000000
> panic: ram_attach: resource 5 failed to attach
>
> I do not see anything about this that looks inherently RPi*
> specific for possibly ending up with an analogous panic. So
> I expect the example is sufficient context to identify a
> problem is present, despite EDK2 use not being normal for
> RPi4B's and the like as far as FreeBSD is concerned.
>

I'm not quite clear why phys_avail changes and why that is triggered by the
906bcc44641d commit. I'm wondering if it makes sense to arrange for
ram_attach to happen before acpi, e.g. using BUS_PASS_ORDER_FIRST?

Doug.