Messages in this thread | | | Subject | Re: [PATCH v2] Revert "ACPI: Add memory semantics to acpi_os_map_memory()" | From | "Rafael J. Wysocki" <> | Date | Tue, 28 Sep 2021 19:26:52 +0200 |
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On 9/24/2021 11:04 AM, Lorenzo Pieralisi wrote: > On Thu, Sep 23, 2021 at 02:54:52PM +0200, Rafael J. Wysocki wrote: >> On Thu, Sep 23, 2021 at 2:26 PM Mark Kettenis <mark.kettenis@xs4all.nl> wrote: >>>> From: "Rafael J. Wysocki" <rafael@kernel.org> >>>> Date: Thu, 23 Sep 2021 13:05:05 +0200 >>>> >>>> On Thu, Sep 23, 2021 at 11:40 AM Lorenzo Pieralisi >>>> <lorenzo.pieralisi@arm.com> wrote: >>>>> On Thu, Sep 23, 2021 at 01:09:58AM +0200, Mark Kettenis wrote: >>>>>>> Date: Wed, 22 Sep 2021 17:33:36 +0100 >>>>>>> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> >>>>>>> >>>>>>> On Fri, Sep 10, 2021 at 10:32:23PM +0800, Jia He 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. >>>>>>>> >>>>>>>> Fixes: 437b38c51162 ("ACPI: Add memory semantics to acpi_os_map_memory()") >>>>>>>> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> >>>>>>>> Cc: Ard Biesheuvel <ardb@kernel.org> >>>>>>>> Cc: Hanjun Guo <guohanjun@huawei.com> >>>>>>>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>>>>>>> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >>>>>>>> Cc: Harb Abdulhamid <harb@amperecomputing.com> >>>>>>>> >>>>>>>> Signed-off-by: Jia He <justin.he@arm.com> >>>>>>> Rewrote the commit log, please take the patch below and repost >>>>>>> it as a v3. >>>>>>> >>>>>>> It would still be great if Ampere can help us understand why >>>>>>> the NormalNC attributes trigger a sync abort on the opregion >>>>>>> before merging it. >>>>>> To be honest, I don't think you really need an explanation from Ampere >>>>>> here. Mapping a part of the address space that doesn't provide memory >>>>>> semantics with NormalNC attributes is wrong and triggering a sync >>>>>> abort in that case is way better than silently ignoring the access. >>>>> That's understood and that's what I explained in the revert commit >>>>> log, no question about it. >>>>> >>>>> I was just asking to confirm if that's what's actually happening. >>>>> >>>>>> Putting my OpenBSD hat on (where we have our own ACPI OSPM >>>>>> implementation) I must say that we always interpreted SystemMemory as >>>>>> memory mapped IO and I think that is a logical choice as SystemIO is >>>>>> used for (non-memory mapped) IO. And I'd say that the ACPI OSPM code >>>>>> should make sure that it uses properly aligned access to any Field >>>>>> object that doesn't use AnyAcc as its access type. Even on x86! And >>>>>> I'd say that AML that uses AnyAcc fields for SystemMemory OpRegions on >>>>>> arm64 is buggy. >>>>>> >>>>>> But maybe relaxing this when the EFI memory map indicates that the >>>>>> address space in question does provide memory semantics does make >>>>>> sense. That should defenitely be documented in the ACPI standard >>>>>> though. >>>>> Mapping SystemMemory Opregions as "memory" does not make sense >>>>> at all to me. Still, that's what Linux ACPICA code does (*if* >>>>> that's what acpi_os_map_memory() is supposed to mean). >>>>> >>>>> https://lore.kernel.org/linux-acpi/20210916160827.GA4525@lpieralisi >>>> It doesn't need to do that, though, if there are good enough arguments >>>> to change the current behavior (and the argument here is that it may >>>> be an MMIO region, so mapping it as memory doesn't really work, but it >>>> also may be a region in memory - there is no rule in the spec by which >>>> SystemMemory Opregions cannot be "memory" AFAICS) and if that change >>>> doesn't introduce regressions in the installed base. >>>> >>>>> Where do we go from here, to be defined, we still have a bug >>>>> to fix after the revert is applied. >>>>> >>>>> drivers/acpi/sysfs.c >>>>> >>>>> maps BERT error regions with acpi_os_map_memory(). >>>> That mechanism is basically used for exporting ACPI tables to user >>>> space and they are known to reside in memory. Whether or not BERT >>>> regions should be mapped in the same way is a good question. >>> It is not inconceivable that BERT regions actually live in memory of >>> the BMC that is exposed over a bus that doesn't implement memory >>> semantics is it? >> No, it isn't, which is why I think that mapping them as RAM may not be >> a good idea in general. > Should I patch acpi_data_show() to map BERT error regions (well, that's > what acpi_data_show() is used on at the moment) as MMIO and use the > related memcpy routine to read them then :) ?
It actually would be good to clean it up so it is clear that this is only used for BERT.
And then there is this question: if this is not RAM (so effectively it is device memory), should it be exposed directly to user space?
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