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

[Lorenzo Pieralisi]

On Mon, Sep 20, 2021 at 07:32:56PM +0200, Rafael J. Wysocki wrote:
> On Mon, Sep 20, 2021 at 7:03 PM Lorenzo Pieralisi
> <lorenzo.pieralisi@xxxxxxx> 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@xxxxxxx> 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.

Thank you Rafael. The mechanism we are currently relying on is the EFI
memory map but if the Opregion address is not described there then we
are left with a default choice to make (theoretically I may also parse
all _CRS in the namespace to find whether a resource include the
Opregion and I may infer attributes from the _CRS resource entry).

Maybe we should update the ACPI specs to enforce it; with current
firmware the idea of using the OS expected *usage* of memory (ie
memory vs IO) described by the mapping function prototype can't work
as this revert shows (even though it would be better if I manage
to find what the precise issue is).

We can't map something with specific attributes if we don't know
whether the physical address space backing the region supports it.

I am left with little choice: I assume the best thing I could do
to fix the original bug is to use ioremap_* in acpi_data_show()
instead of acpi_os_map/unmap_memory() to map that memory with
specific attributes (for BERT error regions, they must be RAM
so, _hopefully_, we know it can be mapped with eg normal memory
mappings).

Thoughts ?

Thanks a lot,
Lorenzo

> > > 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