Re: [PATCH v2] Revert "ACPI: Add memory semantics to acpi_os_map_memory()"

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Sep 10, 2021 at 07:28:49PM +0200, Ard Biesheuvel wrote:
> On Fri, 10 Sept 2021 at 16:32, Jia He <justin.he@arm.com> wrote:
> >
> > This reverts commit 437b38c51162f8b87beb28a833c4d5dc85fa864e.
> >
> > After this commit, a boot panic is alway hit on an Ampere EMAG server
> > with call trace as follows:
> >  Internal error: synchronous external abort: 96000410 [#1] SMP
> >  Modules linked in:
> >  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0+ #462
> >  Hardware name: MiTAC RAPTOR EV-883832-X3-0001/RAPTOR, BIOS 0.14 02/22/2019
> >  pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > [...snip...]
> >  Call trace:
> >   acpi_ex_system_memory_space_handler+0x26c/0x2c8
> >   acpi_ev_address_space_dispatch+0x228/0x2c4
> >   acpi_ex_access_region+0x114/0x268
> >   acpi_ex_field_datum_io+0x128/0x1b8
> >   acpi_ex_extract_from_field+0x14c/0x2ac
> >   acpi_ex_read_data_from_field+0x190/0x1b8
> >   acpi_ex_resolve_node_to_value+0x1ec/0x288
> >   acpi_ex_resolve_to_value+0x250/0x274
> >   acpi_ds_evaluate_name_path+0xac/0x124
> >   acpi_ds_exec_end_op+0x90/0x410
> >   acpi_ps_parse_loop+0x4ac/0x5d8
> >   acpi_ps_parse_aml+0xe0/0x2c8
> >   acpi_ps_execute_method+0x19c/0x1ac
> >   acpi_ns_evaluate+0x1f8/0x26c
> >   acpi_ns_init_one_device+0x104/0x140
> >   acpi_ns_walk_namespace+0x158/0x1d0
> >   acpi_ns_initialize_devices+0x194/0x218
> >   acpi_initialize_objects+0x48/0x50
> >   acpi_init+0xe0/0x498
> >
> > As mentioned by Lorenzo:
> >   "We are forcing memory semantics mappings to PROT_NORMAL_NC, which
> >   eMAG does not like at all and I'd need to understand why. It looks
> >   like the issue happen in SystemMemory Opregion handler."
> >
> > Hence just revert it before everything is clear.
> >
> 
> Can we try to find the root cause first? -rc1 is not even out yet, and
> reverting it now means we can not resubmit it until the next merge
> window.

Yes, absolutely. We need to understand where the problem is, because it
looks like we can't map SystemMemory Opregion with NORMAL_NC if the PA
is not in the EFI map, that's a problem (ie how can we determine the
right memory attributes for SystemMemory Operation regions then) but
let's not speculate and find what the issue is first.

Lorenzo