On Thu, Mar 21, 2019 at 08:26:20PM +0000, Andrew Cooper wrote:
> It turns out that this code was previously dead.
>
> c/s dcf41790 " x86/mmcfg/drhd: Move acpi_mmcfg_init() call before calling
> acpi_parse_dmar()" resulted in PCI segment 0 now having been initialised
> enough for acpi_parse_one_drhd() to not take the
>
> /* Skip checking if segment is not accessible yet. */
>
> path unconditionally. However, some systems have DMAR tables which list
> devices which are disabled by user choice (in particular, Dell PowerEdge R740
> with I/O AT DMA disabled), and turning off all IOMMU functionality in this
> case is entirely unhelpful behaviour.
>
> Leave the warning which identifies the problematic devices, but drop the
> remaining logic. This leaves the system in better overall state, and working
> in the same way that it did in previous releases.
>
> Reported-by: Igor Druzhinin <igor.druzhi...@citrix.com>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Reviewed-by: Roger Pau Monné <roger....@citrix.com>
I think this is a more sane behavior.
> - if ( invalid_cnt )
> - {
> - if ( iommu_workaround_bios_bug &&
> - invalid_cnt == dmaru->scope.devices_cnt )
> - {
> - printk(XENLOG_WARNING VTDPREFIX
> - " Workaround BIOS bug: ignoring DRHD (no devices in
> its scope are PCI discoverable)\n");
> -
> - scope_devices_free(&dmaru->scope);
> - iommu_free(dmaru);
> - xfree(dmaru);
> - }
> - else
> - {
> - printk(XENLOG_WARNING VTDPREFIX
> - " DRHD is invalid (some devices in its scope are not
> PCI discoverable)\n");
> - printk(XENLOG_WARNING VTDPREFIX
> - " Try \"iommu=force\" or
> \"iommu=workaround_bios_bug\" if you really want VT-d\n");
> - ret = -EINVAL;
> - }
The workaround_bios_bug option seems quite pointless anyway, it only
prevents propagating the error to the caller if all the devices in the
DMAR scope are non-existent, or else the DMAR won't be registered
and an error would be returned to the caller.
Thanks, Roger.
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