On 20/08/2025 12:33 pm, Roger Pau Monné wrote: > On Tue, Aug 19, 2025 at 07:23:57PM +0100, Andrew Cooper wrote: >> On 19/08/2025 6:18 pm, Roger Pau Monne wrote: >>> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c >>> index 6fb42c5a5f95..bd648323bfed 100644 >>> --- a/xen/arch/x86/setup.c >>> +++ b/xen/arch/x86/setup.c >>> @@ -1938,11 +1938,10 @@ void asmlinkage __init noreturn __start_xen(void) >>> setup_system_domains(); >>> >>> /* >>> - * Ahead of any ACPI table parsing make sure we have control structures >>> - * for PCI segment 0. >>> + * Initialize PCI (create segment 0, setup MMCFG access) ahead of IOMMU >>> + * setup, as it requires access to the PCI config space. >>> */ >> Again, this isn't terribly clear IMO. >> >> "ahead of IOMMU setup, as the IOMMUs might not all live on segment 0." ? > It's not just IOMMUs, but for example on VT-d we also need to poke at > the config space of bridges, and when such bridges live in segment > 0 > that results in garbage being returned. > > I'm not sure acpi_iommu_init() accesses the IOMMU PCI device config > space, but it does at least access the config space of bridges in > order to detect hierarchy. See how acpi_parse_dev_scope() performs > PCI reads. > > What about using: > > /* > * Initialize PCI (create segment 0, setup MMCFG access) ahead of IOMMU > * setup, as devices in segment > 0 must also be discoverable. > */
Yeah, that works. With those comment adjustments, Reviewed-by: Andrew Cooper <andrew.coop...@citrix.com>
