Re: [PATCH v3 3/3] x86/dom0: be less restrictive with the Interrupt Address Range

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.02.2025 17:48, 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

Nit: Missing "in"?

> dom0.  Note that the restriction to map the local APIC page is enforced
> separately, and that continues to be present.  Additionally make sure the
> emulated local APIC page is also not mapped, in case dom0 is using it.

But that's in GFN space, not in MFN one. Why would that matter for iomem_caps?

Jan