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

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Sep 20, 2021 at 7:03 PM Lorenzo Pieralisi
<lorenzo.pieralisi@arm.com> wrote:
>
> On Thu, Sep 16, 2021 at 05:08:27PM +0100, Lorenzo Pieralisi wrote:
> > 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.
> >
> > I am waiting to debug this on an eMAG but I noticed something that
> > I wanted to bring up.
> >
> > SystemMemory Operation region handler - ie
> >
> > acpi_ex_system_memory_space_handler()
> >
> > maps the Operation Region (that AFAICS is MMIO, it is _not_ memory)
> > with acpi_os_map_memory() and I believe that's what is causing this
> > bug.
> >
> > On the other hand, acpi_os_map_generic_address(), to handle spaceid
> > ACPI_ADR_SPACE_SYSTEM_MEMORY, uses acpi_os_map_iomem() that is more
> > in line with my expectations.
>
> Hi Rafael,
>
> I wanted to ask please if you have any insights on why
>
> (1) acpi_ex_system_memory_space_handler()
> (2) acpi_os_map_generic_address()
>
> Use two different calls to map memory for the _same_ address space ID
> (SystemMemory).
>
> (3) acpi_os_map_memory()
> vs
> (4) acpi_os_map_iomem()

I don't really have a good answer here.

On x86 this doesn't really matter and that's where
acpi_ex_system_memory_space_handler() was first introduced.  It is not
only used for IOMEM (there are SystemMemory operation regions in RAM),
but since it may be in IOMEM, it should assume so.

> I am struggling to understand why (1) uses (3) ("memory semantics") when
> (2) uses (4) - it is actually unclear how the distinction between
> the two mapping APIs is to be drawn and on what basis one should
> choose which one to use.
>
> I am still waiting to grab some HW to debug this report but the issue
> here is that we are mapping an OpRegion SystemMemory with (3) in the
> memory space handler and given the patch we are reverting we end up
> mapping the operation region with normal non-cacheable memory attributes
> that probably the physical address range behind the OpRegion does not
> support.

If that is the case, there needs to be a mechanism to decide what kind
of mapping to use for SystemMemory operation regions based on the type
of physical memory the address range in question is located in.


> > Question is: is the mapping in acpi_ex_system_memory_space_handler()
> > wrong (and should be patched with acpi_os_map_iomem() ?)
> >
> > On x86 this should not change a thing, on ARM it would.
> >
> > I don't think it is right to map SystemMemory Operation regions with
> > memory semantics but on the other hand, other than the EFI memory map,
> > there is nothing we can do to determine what a SystemMemory Operation
> > region address space actually represents.
> >
> > Thoughts ? Before embarking on patching
> >
> > acpi_ex_system_memory_space_handler()
> >
> > I want to make sure my understanding of the SystemMemory space is
> > correct, comments welcome.
> >
> > I will pinpoint the trigger for this bug shortly and before doing
> > anything else.
> >
> > Thanks,
> > Lorenzo