Re: [PATCH 10/11] xen/arm: Do not map PCI ECAM space to Domain-0's p2m

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 16 Sep 2021, Oleksandr Andrushchenko wrote:
> On 15.09.21 23:19, Stefano Stabellini wrote:
> > On Wed, 15 Sep 2021, Stefano Stabellini wrote:
> >> On Wed, 15 Sep 2021, Oleksandr Andrushchenko wrote:
> >>> On 15.09.21 03:36, Stefano Stabellini wrote:
> >>>> On Tue, 14 Sep 2021, Oleksandr Andrushchenko wrote:
> >>>>> With the patch above I have the following log in Domain-0:
> >>>>>
> >>>>> generic-armv8-xt-dom0 login: root
> >>>>> root@generic-armv8-xt-dom0:~# (XEN) *** Serial input to Xen (type 
> >>>>> 'CTRL-a' three times to switch input)
> >>>>> (XEN) ==== PCI devices ====
> >>>>> (XEN) ==== segment 0000 ====
> >>>>> (XEN) 0000:03:00.0 - d0 - node -1
> >>>>> (XEN) 0000:02:02.0 - d0 - node -1
> >>>>> (XEN) 0000:02:01.0 - d0 - node -1
> >>>>> (XEN) 0000:02:00.0 - d0 - node -1
> >>>>> (XEN) 0000:01:00.0 - d0 - node -1
> >>>>> (XEN) 0000:00:00.0 - d0 - node -1
> >>>>> (XEN) *** Serial input to DOM0 (type 'CTRL-a' three times to switch 
> >>>>> input)
> >>>>>
> >>>>> root@generic-armv8-xt-dom0:~# modprobe e1000e
> >>>>> [   46.104729] e1000e: Intel(R) PRO/1000 Network Driver
> >>>>> [   46.105479] e1000e: Copyright(c) 1999 - 2015 Intel Corporation.
> >>>>> [   46.107297] e1000e 0000:03:00.0: enabling device (0000 -> 0002)
> >>>>> (XEN) map [e0000, e001f] -> 0xe0000 for d0
> >>>>> (XEN) map [e0020, e003f] -> 0xe0020 for d0
> >>>>> [   46.178513] e1000e 0000:03:00.0: Interrupt Throttling Rate 
> >>>>> (ints/sec) set to dynamic conservative mode
> >>>>> [   46.189668] pci_msi_setup_msi_irqs
> >>>>> [   46.191016] nwl_compose_msi_msg msg at fe440000
> >>>>> (XEN) traps.c:2014:d0v0 HSR=0x00000093810047 pc=0xffff8000104b4b00 
> >>>>> gva=0xffff800010fa5000 gpa=0x000000e0040000
> >>>>> [   46.200455] Unhandled fault at 0xffff800010fa5000
> >>>>>
> >>>>> [snip]
> >>>>>
> >>>>> [   46.233079] Call trace:
> >>>>> [   46.233559]  __pci_write_msi_msg+0x70/0x180
> >>>>> [   46.234149]  pci_msi_domain_write_msg+0x28/0x30
> >>>>> [   46.234869]  msi_domain_activate+0x5c/0x88
> >>>>>
> >>>>>    From the above you can see that BARs are mapped for Domain-0 now
> >>>>>
> >>>>> only when an assigned PCI device gets enabled in Domain-0.
> >>>>>
> >>>>> Another thing to note is that we crash on MSI-X access as BARs are 
> >>>>> mapped
> >>>>>
> >>>>> to the domain while enabling memory decoding in the COMMAND register,
> >>>>>
> >>>>> but MSI-X are handled differently, e.g. we have MSI-X holes in the 
> >>>>> mappings.
> >>>>>
> >>>>> This is because before this change the whole PCI aperture was mapped 
> >>>>> into
> >>>>>
> >>>>> Domain-0 and it is not. Thus, MSI-X holes are left unmapped now and 
> >>>>> there
> >>>>>
> >>>>> was no need to do so, e.g. they were always mapped into Domain-0 and
> >>>>>
> >>>>> emulated for guests.
> >>>>>
> >>>>> Please note that one cannot use xl pci-attach in this case to attach 
> >>>>> the PCI device
> >>>>>
> >>>>> in question to Domain-0 as (please see the log) that device is already 
> >>>>> attached.
> >>>>>
> >>>>> Neither it can be detached and re-attached. So, without mapping MSI-X 
> >>>>> holes for
> >>>>>
> >>>>> Domain-0 the device becomes unusable in Domain-0. At the same time the 
> >>>>> device
> >>>>>
> >>>>> can be successfully passed to DomU.
> >>>>>
> >>>>>
> >>>>> Julien, Stefano! Please let me know how can we proceed with this.
> >>>> What was the plan for MSI-X in Dom0?
> >>> It just worked because we mapped everything
> >>>> Given that Dom0 interacts with a virtual-ITS and virtual-GIC rather than
> >>>> a physical-ITS and physical-GIC, I imagine that it wasn't correct for
> >>>> Dom0 to write to the real MSI-X table directly?
> >>>>
> >>>> Shouldn't Dom0 get emulated MSI-X tables like any DomU?
> >>>>
> >>>> Otherwise, if Dom0 is expected to have the real MSI-X tables mapped, then
> >>>> I would suggest to map them at the same time as the BARs. But I am
> >>>> thinking that Dom0 should get emulated MSI-X tables, not physical MSI-X
> >>>> tables.
> >>> Yes, it seems more than reasonable to enable emulation for Domain-0
> >>>
> >>> as well. Other than that, Stefano, do you think we are good to go with
> >>>
> >>> the changes I did in order to unmap everything for Domain-0?
> >>
> >> It might be better to resend the series with the patch in it, because it
> >> is difficult to review the patch like this.
> 
> This is true. Taking into account Xen release plan I am just trying to
> 
> minimize the turn around here. Sorry about this
> 
> >>   Nonetheless I tried, but I
> >> might have missed something.
> Thank you for your time!!
> >>
> >> Previously the whole PCIe bridge aperture was mapped to Dom0, and
> >> it was done by map_range_to_domain, is that correct?
> 
> Yes, but not only the aperture: please see below.
> 
> 
> >>
> >> Now this patch, to avoid mapping the entire aperture to Dom0, is
> >> skipping any operations for PCIe devices in map_range_to_domain by
> >> setting need_mapping = false.
> >>
> >> The idea is that instead, we'll only map things when needed and not the
> >> whole aperture. However, looking at the changes to
> >> pci_host_bridge_mappings (formerly known as
> >> pci_host_bridge_need_p2m_mapping), it is still going through the full
> >> list of address ranges of the PCIe bridge and map each range one by one
> >> using map_range_to_domain. Also, pci_host_bridge_mappings is still
> >> called unconditionally at boot for Dom0.
> >>
> >> So I am missing the part where the aperture is actually *not* mapped to
> >> Dom0.
> With map_range_to_domain we also mapped all the entries
> 
> of the "reg" and "ranges" properties. Let's have a look at [1]:
> 
> - ranges         : As described in IEEE Std 1275-1994, but must provide
>                     at least a definition of non-prefetchable memory. One
>                     or both of prefetchable Memory and IO Space may also
>                     be provided.
> 
> - reg            : The Configuration Space base address and size, as accessed
>                     from the parent bus.  The base address corresponds to
>                     the first bus in the "bus-range" property.  If no
>                     "bus-range" is specified, this will be bus 0 (the 
> default).
> 
> The most interesting comes when "reg" also has other then configuration
> 
> space addresses, for example [2]:
> 
> - reg: Should contain rc_dbi, config registers location and length.
> - reg-names: Must include the following entries:
>    "rc_dbi": controller configuration registers;
>    "config": PCIe configuration space registers.
> 
> So, we don't need to map "ranges" and *config* from the "reg", but all
> 
> the rest from "reg" still needs to be mapped to Domain-0, so the PCIe
> 
> bridge can remain functional in Domain-0.
> 
> >>   What's the difference between the loop in
> >> pci_host_bridge_mappings:
> >>
> >>    for ( i = 0; i < dt_number_of_address(dev); i++ )
> >>      map_range_to_domain...
> >>
> >> and the previous code in map_range_to_domain? I think I am missing
> >> something but as mentioned it is difficult to review the patch like this
> >> out of order.
> >>
> >> Also, and this is minor, even if currently unused, it might be good to
> >> keep a length parameter to pci_host_bridge_need_p2m_mapping.
> > It looks like the filtering is done based on:
> >
> > return cfg->phys_addr != addr
> 
> As I explained above it is *now* the only range that we *do not want* to
> 
> be mapped to Domain-0. Other "reg" entries still need to be mapped.
> 
> >
> > in pci_ecam_need_p2m_mapping that is expected to filter out the address
> > ranges we don't want to map because it comes from
> > xen/arch/arm/pci/pci-host-common.c:gen_pci_init:
> >
> >      /* Parse our PCI ecam register address*/
> >      err = dt_device_get_address(dev, ecam_reg_idx, &addr, &size);
> >      if ( err )
> >          goto err_exit;
> >
> > In pci_host_bridge_mappings, instead of parsing device tree again, can't
> > we just fetch the address and length we need to map straight from
> > bridge->sysdata->phys_addr/size ?
> 
> We can't as the address describes the configuration space which we
> 
> *do not* want to be mapped, but what we want is other than configuration
> 
> entries in the "reg" property.
> 
> >
> > At the point when pci_host_bridge_mappings is called in your new patch,
> > we have already initialized all the PCIe-related data structures. It
> > seems a bit useless to have to go via device tree again.
> 
> Bottom line: we do need to go over the "reg" property and map the regions
> 
> of which PCIe bridge is dependent and only skip "config" part of it.

OK, thanks for the explanation, please add it to the commit message
and/or as an in-code comment when you resend the patch