Re: [PATCH v2 2/2] x86/dom0: be less restrictive with the Interrupt Address Range

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.02.2025 15:16, Roger Pau Monne wrote:
> Xen currently prevents dom0 from creating CPU or IOMMU page-table mappings
> into the interrupt address range [0xfee00000, 0xfeefffff].  This range has
> two different purposes.  For accesses from the CPU is contains the default
> position of local APIC page at 0xfee00000.  For accesses from devices
> it's the MSI address range, so the address field in the MSI entries
> (usually) point to an address on that range to trigger an interrupt.
> 
> There are reports of Lenovo Thinkpad devices placing what seems to be the
> UCSI shared mailbox at address 0xfeec2000 in the interrupt address range.
> Attempting to use that device with a Linux PV dom0 leads to an error when
> Linux kernel maps 0xfeec2000:
> 
> RIP: e030:xen_mc_flush+0x1e8/0x2b0
>  xen_leave_lazy_mmu+0x15/0x60
>  vmap_range_noflush+0x408/0x6f0
>  __ioremap_caller+0x20d/0x350
>  acpi_os_map_iomem+0x1a3/0x1c0
>  acpi_ex_system_memory_space_handler+0x229/0x3f0
>  acpi_ev_address_space_dispatch+0x17e/0x4c0
>  acpi_ex_access_region+0x28a/0x510
>  acpi_ex_field_datum_io+0x95/0x5c0
>  acpi_ex_extract_from_field+0x36b/0x4e0
>  acpi_ex_read_data_from_field+0xcb/0x430
>  acpi_ex_resolve_node_to_value+0x2e0/0x530
>  acpi_ex_resolve_to_value+0x1e7/0x550
>  acpi_ds_evaluate_name_path+0x107/0x170
>  acpi_ds_exec_end_op+0x392/0x860
>  acpi_ps_parse_loop+0x268/0xa30
>  acpi_ps_parse_aml+0x221/0x5e0
>  acpi_ps_execute_method+0x171/0x3e0
>  acpi_ns_evaluate+0x174/0x5d0
>  acpi_evaluate_object+0x167/0x440
>  acpi_evaluate_dsm+0xb6/0x130
>  ucsi_acpi_dsm+0x53/0x80
>  ucsi_acpi_read+0x2e/0x60
>  ucsi_register+0x24/0xa0
>  ucsi_acpi_probe+0x162/0x1e3
>  platform_probe+0x48/0x90
>  really_probe+0xde/0x340
>  __driver_probe_device+0x78/0x110
>  driver_probe_device+0x1f/0x90
>  __driver_attach+0xd2/0x1c0
>  bus_for_each_dev+0x77/0xc0
>  bus_add_driver+0x112/0x1f0
>  driver_register+0x72/0xd0
>  do_one_initcall+0x48/0x300
>  do_init_module+0x60/0x220
>  __do_sys_init_module+0x17f/0x1b0
>  do_syscall_64+0x82/0x170
> 
> Remove the restrictions to create mappings the interrupt address range for
> dom0.  Note that the restriction to map the local APIC page is enforced
> separately, and that continues to be present.
> 
> Note that even if the interrupt address range entries are populated in the
> IOMMU page-tables no device access will reach those pages.  Device accesses
> to the Interrupt Address Range will always be converted into Interrupt
> Messages and are not subject to DMA remapping.
> 
> There's also the following restriction noted in Intel VT-d:
> 
>> Software must not program paging-structure entries to remap any address to
>> the interrupt address range. Untranslated requests and translation requests
>> that result in an address in the interrupt range will be blocked with
>> condition code LGN.4 or SGN.8. Translated requests with an address in the
>> interrupt address range are treated as Unsupported Request (UR).
> 
> Similarly for AMD-Vi:
> 
>> Accesses to the interrupt address range (Table 3) are defined to go through
>> the interrupt remapping portion of the IOMMU and not through address
>> translation processing. Therefore, when a transaction is being processed as
>> an interrupt remapping operation, the transaction attribute of
>> pretranslated or untranslated is ignored.
>>
>> Software Note: The IOMMU should
>> not be configured such that an address translation results in a special
>> address such as the interrupt address range.
> 
> However those restrictions don't apply to the identity mappings possibly
> created for dom0, since the interrupt address range is never subject to DMA
> remapping, and hence there's no output address after translation that
> belongs to the interrupt address range.
> 
> Reported-by: Jürgen Groß <jgross@xxxxxxxx>
> Link: 
> https://lore.kernel.org/xen-devel/baade0a7-e204-4743-bda1-282df74e5f89@xxxxxxxx/
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>