Re: Problems in PV dom0 on recent x86 hardware

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.07.2024 23:30, Jason Andryuk wrote:
> On 2024-07-08 05:12, Jan Beulich wrote:
>> On 08.07.2024 11:08, Roger Pau Monné wrote:
>>> On Mon, Jul 08, 2024 at 10:37:22AM +0200, Jan Beulich wrote:
>>>> On 08.07.2024 10:15, Jürgen Groß wrote:
>>>>> I've got an internal report about failures in dom0 when booting with
>>>>> Xen on a Thinkpad P14s Gen 3 AMD (kernel 6.9).
>>>>>
>>>>> With some debugging I've found that the UCSI driver seems to fail to
>>>>> map MFN feec2 as iomem, as the hypervisor is denying this mapping due
>>>>> to being part of the MSI space. The mapping attempt seems to be the
>>>>> result of an ACPI call of the UCSI driver:
>>>>>
>>>>> [   44.575345] RIP: e030:xen_mc_flush+0x1e8/0x2b0
>>>>> [   44.575418]  xen_leave_lazy_mmu+0x15/0x60
>>>>> [   44.575425]  vmap_range_noflush+0x408/0x6f0
>>>>> [   44.575438]  __ioremap_caller+0x20d/0x350
>>>>> [   44.575450]  acpi_os_map_iomem+0x1a3/0x1c0
>>>>> [   44.575454]  acpi_ex_system_memory_space_handler+0x229/0x3f0
>>>>> [   44.575464]  acpi_ev_address_space_dispatch+0x17e/0x4c0
>>>>> [   44.575474]  acpi_ex_access_region+0x28a/0x510
>>>>> [   44.575479]  acpi_ex_field_datum_io+0x95/0x5c0
>>>>> [   44.575482]  acpi_ex_extract_from_field+0x36b/0x4e0
>>>>> [   44.575490]  acpi_ex_read_data_from_field+0xcb/0x430
>>>>> [   44.575493]  acpi_ex_resolve_node_to_value+0x2e0/0x530
>>>>> [   44.575496]  acpi_ex_resolve_to_value+0x1e7/0x550
>>>>> [   44.575499]  acpi_ds_evaluate_name_path+0x107/0x170
>>>>> [   44.575505]  acpi_ds_exec_end_op+0x392/0x860
>>>>> [   44.575508]  acpi_ps_parse_loop+0x268/0xa30
>>>>> [   44.575515]  acpi_ps_parse_aml+0x221/0x5e0
>>>>> [   44.575518]  acpi_ps_execute_method+0x171/0x3e0
>>>>> [   44.575522]  acpi_ns_evaluate+0x174/0x5d0
>>>>> [   44.575525]  acpi_evaluate_object+0x167/0x440
>>>>> [   44.575529]  acpi_evaluate_dsm+0xb6/0x130
>>>>> [   44.575541]  ucsi_acpi_dsm+0x53/0x80
>>>>> [   44.575546]  ucsi_acpi_read+0x2e/0x60
>>>>> [   44.575550]  ucsi_register+0x24/0xa0
>>>>> [   44.575555]  ucsi_acpi_probe+0x162/0x1e3
>>>>> [   44.575559]  platform_probe+0x48/0x90
>>>>> [   44.575567]  really_probe+0xde/0x340
>>>>> [   44.575579]  __driver_probe_device+0x78/0x110
>>>>> [   44.575581]  driver_probe_device+0x1f/0x90
>>>>> [   44.575584]  __driver_attach+0xd2/0x1c0
>>>>> [   44.575587]  bus_for_each_dev+0x77/0xc0
>>>>> [   44.575590]  bus_add_driver+0x112/0x1f0
>>>>> [   44.575593]  driver_register+0x72/0xd0
>>>>> [   44.575600]  do_one_initcall+0x48/0x300
>>>>> [   44.575607]  do_init_module+0x60/0x220
>>>>> [   44.575615]  __do_sys_init_module+0x17f/0x1b0
>>>>> [   44.575623]  do_syscall_64+0x82/0x170
>>>>> [   44.575685] 1 of 1 multicall(s) failed: cpu 4
>>>>> [   44.575695]   call  1: op=1 result=-1 
>>>>> caller=xen_extend_mmu_update+0x4e/0xd0
>>>>> pars=ffff888267e25ad0 1 0 7ff0 args=9ba37a678 80000000feec2073
>>>>>
>>>>> The pte value of the mmu_update call is 80000000feec2073, which is 
>>>>> rejected by
>>>>> the hypervisor with -EPERM.
>>>>>
>>>>> Before diving deep into the UCSI internals, is it possible that the 
>>>>> hypervisor
>>>>> needs some update (IOW: could it be the mapping attempt should rather be
>>>>> honored, as there might be an I/O resources at this position which dom0 
>>>>> needs
>>>>> to access for using the related hardware?)
>>>>
>>>> Adding to Andrew's reply: Is there any BAR in the system covering that 
>>>> address?
>>>> Or is it rather ACPI "making up" that address (which would remind me of 
>>>> IO-APIC
>>>> space being accessed by certain incarnations of ACPI, resulting in similar
>>>> issues)?
>>>
>>> So you think ACPI is using some kind of backdoor to access the local
>>> APIC registers?
>>
>> No, I'm wondering if they're trying to access *something*. As it stands we
>> don't even know what kind of access is intended; all we know is that they're
>> trying to map that page (and maybe adjacent ones).
> 
>  From the backtrace, it looks like the immediate case is just trying to 
> read a 4-byte version:
> 
>  >>>> [   44.575541]  ucsi_acpi_dsm+0x53/0x80
>  >>>> [   44.575546]  ucsi_acpi_read+0x2e/0x60
>  >>>> [   44.575550]  ucsi_register+0x24/0xa0
>  >>>> [   44.575555]  ucsi_acpi_probe+0x162/0x1e3
> 
> int ucsi_register(struct ucsi *ucsi)
> {
>          int ret;
> 
>          ret = ucsi->ops->read(ucsi, UCSI_VERSION, &ucsi->version,
>                                sizeof(ucsi->version));
> 
> ->read being ucsi_acpi_read()
> 
> However, the driver also appears write to adjacent addresses.

There are also corresponding write functions in the driver, yes, but
ucsi_acpi_async_write() (used directly or indirectly) similarly calls
ucsi_acpi_dsm(), which wires through to acpi_evaluate_dsm(). That's
ACPI object evaluation, which isn't obvious without seeing the
involved AML whether it might write said memory region. The writing
done in the write function(s) looks to be

        memcpy(ua->base + offset, val, val_len);

with their read counterpart being

        memcpy(val, ua->base + offset, val_len);

where ua->base may well be an entirely different address (looks like
it's the first of the BARs as per ucsi_acpi_probe()).

If acpi_evaluate_dsm() would only ever read the region, an option (if
all else fails) might be to similarly (to what we do for IO-APICs)
permit read accesses / mappings (by inserting the range into
mmio_ro_ranges). Yet of course first we need to better understand
what's actually going on here.

Jan