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[Xen-devel] Re: [PATCH 0 of 3] Patches for PCI passthrough with modified

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 0 of 3] Patches for PCI passthrough with modified E820 (v3) - resent.
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Mon, 9 May 2011 10:00:30 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On Wed, 2011-05-04 at 15:17 +0100, Konrad Rzeszutek Wilk wrote:
> Hello,
> This set of v3 patches allows a PV domain to see the machine's
> E820 and figure out where the "PCI I/O" gap is and match it with the reality.
> Changelog since v2 posting:
>  - Moved 'libxl__e820_alloc' to be called from do_domain_create and if
>    machine_e820 == true.
>  - Made no_machine_e820 be set to true, if the guest has no PCI devices (and 
> is PV)
>  - Used Keir's re-worked code for E820 creation.
> Changelog since v1 posting:
>  - Squashed the "x86: make the pv-only e820 array be dynamic" and 
>    "x86: adjust the size of the e820 for pv guest to be dynamic" together.
>  - Made xc_domain_set_memmap_limit use the 'xc_domain_set_memory_map'
>  - Moved 'libxl_e820_alloc' and 'libxl_e820_sanitize' to be an internal
>    operation and called from 'libxl_device_pci_parse_bdf'.
>  - Expanded 'libxl_device_pci_parse_bdf' API call to have an extra argument
>    (optional).
> The short end is that with these patches a PV domain can:
>  - Use the correct PCI I/O gap. Before these patches, Linux guest would
>    boot up and would tell:
>    [    0.000000] Allocating PCI resources starting at 40000000 (gap: 
> 40000000:c0000000)
>    while in actuality the PCI I/O gap should have been:
>    [    0.000000] Allocating PCI resources starting at b0000000 (gap: 
> b0000000:4c000000)

The reason it needs to be a particular gap is that we can't (easily? at
all?) rewrite the device BARs to match the guest's idea of the hole, is
that right? So it needs to be consistent with the underlying host hole.

I wonder if it is time to enable IOMMU for PV guests by default.
Presumably in that case we can manufacture any hole we like in the e820,
which is useful e.g. when migrating to not-completely-homogeneous hosts.

>  - The PV domain with PCI devices was limited to 3GB. It now can be booted
>    with 4GB, 8GB, or whatever number you want. The PCI devices will now _not_ 
> conflict
>    with System RAM. Meaning the drivers can load.
>  - With 2.6.39 kernels (which has the 1-1 mapping code), the VM_IO flag will 
> be
>    now automatically applied to regions that are considerd PCI I/O regions. 
> You can
>    find out which those are by looking for '1-1' in the kernel bootup.
> To use this patchset, the guest config file has to have the parameter 
> 'pci=['<BDF>',...]'
> enabled.
> This has been tested with 2.6.18 (RHEL5), 2.6.27(SLES11), 2.6.36, 2.6.37, 
> 2.6.38,
> and 2.6.39 kernels. Also tested with PV NetBSD 5.1.
> Tested this with the PCI devices (NIC, MSI), and with 2GB, 4GB, and 6GB guests
> with success.
>  libxc/xc_domain.c      |   77 +++++++++++-----
>  libxc/xc_e820.h        |    3 
>  libxc/xenctrl.h        |   11 ++
>  libxl/libxl.idl        |    1 
>  libxl/libxl_create.c   |    8 +
>  libxl/libxl_internal.h |    1 
>  libxl/libxl_pci.c      |  230 
> +++++++++++++++++++++++++++++++++++++++++++++++++
>  libxl/xl_cmdimpl.c     |    3 
>  8 files changed, 309 insertions(+), 25 deletions(-)

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