Re: [Xen-devel] [PATCH RFC] pvh: set need_iommu early

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Elena Ufimtseva [mailto:elena.ufimtseva@xxxxxxxxxx]
> Sent: Thursday, January 22, 2015 4:53 AM
> 
> need_iommu has to be set earler for dom0 pvh specific init
> functions. If not enabled, mmio regions are not mapped with iommu
> during domain construction.
> 
> This was discovered when working on booting problems of pvh dom0
> on two different machines (ThinkCentre M and Dell 5600T).
> On ThinkCentre during pvh dom0 booting process, IOMMU would report
> Page fault with EPT not present. The memory address of the page fault
> suggested that is mmio region for USB host controllers. The faulting
> address marked as Reserved in e820 map and is not part of any rmrr
> region reported by ACPI.

Need more understanding here. If iommu hasn't been setup for dom0 yet, 
why is there iommu page fault at that point?

> These USB Host controllers have debugging devices which do behave
> strangely and obviously use these mmio addresses for IO.
> In pv dom0 case, all mmio regions are mappped with IOMMUF_readable and
> IOMMUF_writable flags.
> 
> The other part of equation for mmio pvh region mappings is that these are
> typed with p2m_mmio_direct.  When requesting iommu flags based on
> memory
> type in ept_set_entry, it returns 0 and the EPT are not being mapped with
> iommu. To have correct mapping set, p2m_mmio_direct has to map to
> IOMMUF_readable and IOMMUF_writable. This RFC patch is to follow.

I didn't see below patch doing anything related to above...

> 
> Problem discussed in thread
> http://lists.xenproject.org/archives/html/xen-devel
> /2014-12/msg01956.html was also solved by this change and correct memory
> type
> to iommu flags setting.

iirc that thread has a different phenomenon hanging on a iommu reg access.
there is a disconnect how that problem is solved with logic explained in this
patch.

> 
> I would like to ask for comments and opinions as there maybe a better way to
> make these changes.
> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>
> ---
>  xen/arch/x86/domain_build.c     | 4 +++-
>  xen/drivers/passthrough/iommu.c | 2 +-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
> index 7993b17..cf8e776 100644
> --- a/xen/arch/x86/domain_build.c
> +++ b/xen/arch/x86/domain_build.c
> @@ -1500,7 +1500,9 @@ int __init construct_dom0(
> 
>      if ( is_pvh_domain(d) )
>      {
> -        /* finally, fixup the page table, replacing mfns with pfns */
> +     d->need_iommu = 1;
> +
> +     /* finally, fixup the page table, replacing mfns with pfns */
>          pvh_fixup_page_tables_for_hap(v, v_start, v_end);
> 
>          /* the pt has correct pfn for si, now update the mfn in the p2m */
> diff --git a/xen/drivers/passthrough/iommu.c
> b/xen/drivers/passthrough/iommu.c
> index cc12735..d7012cb 100644
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -154,7 +154,7 @@ void __hwdom_init iommu_hwdom_init(struct domain
> *d)
>          return;
> 
>      register_keyhandler('o', &iommu_p2m_table);
> -    d->need_iommu = !!iommu_dom0_strict;
> +    d->need_iommu |= !!iommu_dom0_strict;
>      if ( need_iommu(d) && !iommu_use_hap_pt(d) )
>      {
>          struct page_info *page;
> --
> 2.1.3


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