Re: [PATCH for-4.20?] x86/dom0: be less restrictive with the Interrupt Address Range

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Feb 12, 2025 at 04:38:00PM +0100, 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.
> 
> For PVH dom0 it's important that the restriction is removed from
> arch_iommu_hwdom_init(), as the logic in that function creates mappings in
> both the CPU and the IOMMU page tables for reserved regions in the memory
> map.  The expectation is that the page at 0xfeec2000 will be added to the
> host memory map using the EfiACPIMemoryNVS type, so arch_iommu_hwdom_init()
> will create a mapping for it.
> 
> 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).
> 
> However this restriction doesn't apply to the identity mappings possibly
> created for dom0, since the interrupt address range is never subject to DMA
> remapping.
> 
> Reported-by: Jürgen Groß <jgross@suse.com>
> Link: https://lore.kernel.org/xen-devel/baade0a7-e204-4743-bda1-282df74e5f89@suse.com/
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>  xen/arch/x86/dom0_build.c           | 4 ----
>  xen/drivers/passthrough/x86/iommu.c | 5 -----
>  2 files changed, 9 deletions(-)
> 
> diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
> index e8f5bf5447bc..d1b4ef83b2d0 100644
> --- a/xen/arch/x86/dom0_build.c
> +++ b/xen/arch/x86/dom0_build.c
> @@ -555,10 +555,6 @@ int __init dom0_setup_permissions(struct domain *d)
>          if ( !rangeset_contains_singleton(mmio_ro_ranges, mfn) )
>              rc |= iomem_deny_access(d, mfn, mfn);
>      }
> -    /* MSI range. */
> -    rc |= iomem_deny_access(d, paddr_to_pfn(MSI_ADDR_BASE_LO),
> -                            paddr_to_pfn(MSI_ADDR_BASE_LO +
> -                                         MSI_ADDR_DEST_ID_MASK));
>      /* HyperTransport range. */
>      if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>      {
> diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c
> index 8b1e0596b84a..ec17701c90dd 100644
> --- a/xen/drivers/passthrough/x86/iommu.c
> +++ b/xen/drivers/passthrough/x86/iommu.c
> @@ -475,11 +475,6 @@ void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
>      if ( rc )
>          panic("IOMMU failed to remove Xen ranges: %d\n", rc);
>  
> -    /* Remove any overlap with the Interrupt Address Range. */
> -    rc = rangeset_remove_range(map, 0xfee00, 0xfeeff);
> -    if ( rc )
> -        panic("IOMMU failed to remove Interrupt Address Range: %d\n", rc);
> -

This last chunk is not correct, if the interrupt address range is not
removed, the local APIC page needs to be filtered out, so this should
instead be:

diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c
index 8b1e0596b84a..c53626dfc69d 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -475,10 +475,11 @@ void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
     if ( rc )
         panic("IOMMU failed to remove Xen ranges: %d\n", rc);

-    /* Remove any overlap with the Interrupt Address Range. */
-    rc = rangeset_remove_range(map, 0xfee00, 0xfeeff);
+    /* Remove any overlap with the local APIC page. */
+    rc = rangeset_remove_range(map, paddr_to_pfn(mp_lapic_addr),
+                               paddr_to_pfn(mp_lapic_addr));
     if ( rc )
-        panic("IOMMU failed to remove Interrupt Address Range: %d\n", rc);
+        panic("IOMMU failed to remove local APIC page: %d\n", rc);

     /* If emulating IO-APIC(s) make sure the base address is unmapped. */
     if ( has_vioapic(d) )