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Re: [Xen-devel] [RFC][v2][PATCH 01/14] tools: introduce some new parameters to set rdm policy



On 2015/6/7 19:06, Wei Liu wrote:
On Wed, Jun 03, 2015 at 09:35:16AM +0800, Chen, Tiejun wrote:
[...]

+reserved regions explicitly. And using "host" to include all reserved regions
+reported on this platform which is good to handle hotplug scenario. In the
+future this parameter may be further extended to allow specifying random
+regions, e.g. even those belonging to another platform as a preparation

Extending how? What's your envisaged syntax for those random regions?

We didn't go into details while discussing that design. Maybe we can do
something like this,

rdm="type=host,reserve=strict,rdm_add=size[KMG][@offset[KMG]],size[KMG][@offset[KMG]],..."


This limits the extra regions to type host and strict policy. If that's
what you want then it's fine.

The policy still can be changed with "reserve=". But whatever, I mean this current format is easy to extend :) You know, the hotplug is really a complicated case, we really need to consider more next.

Thanks
Tiejun


Should you want to reserve more, an array is more useful. Could you

Yeah.

provide some examples?

But we may have alternative approach to this when I noticed some guys are
trying to delivery some patches about setting rmrr region by xen
commandline. So I also would like to check this likelihood when we can step
forward.


Makes sense.


+for live migration with passthrough devices.
+
+"none" means we have nothing to do all reserved regions and ignore all 
policies,
+so guest work as before.

[...]

diff --git a/docs/misc/vtd.txt b/docs/misc/vtd.txt
index 9af0e99..7d63c47 100644
--- a/docs/misc/vtd.txt
+++ b/docs/misc/vtd.txt
@@ -111,6 +111,30 @@ in the config file:
  To override for a specific device:
        pci = [ '01:00.0,msitranslate=0', '03:00.0' ]

+RDM, 'reserved device memory', for PCI Device Passthrough
+---------------------------------------------------------
+
+There are some devices the BIOS controls, for e.g. USB devices to perform
+PS2 emulation. The regions of memory used for these devices are marked
+reserved in the e820 map. When we turn on DMA translation, DMA to those
+regions will fail. Hence BIOS uses RMRR to specify these regions along with
+devices that need to access these regions. OS is expected to setup
+identity mappings for these regions for these devices to access these regions.
+
+While creating a VM we should reserve them in advance, and avoid any conflicts.
+So we introduce user configurable parameters to specify RDM resource and
+according policies,
+
+To enable this globally, add "rdm" in the config file:
+
+    rdm = "type=host, reserve=relaxed"   (default policy is "relaxed")
+
+Or just for a specific device:
+
+    pci = [ '01:00.0,rdm_reserve=relaxed', '03:00.0,rdm_reserve=strict' ]
+
+For all the options available to RDM, see xl.cfg(5).
+

  Caveat on Conventional PCI Device Passthrough
  ---------------------------------------------
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index f0da7dc..d649ead 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -100,6 +100,12 @@ static int sched_params_valid(libxl__gc *gc,
      return 1;
  }

+void libxl__rdm_setdefault(libxl__gc *gc, libxl_domain_build_info *b_info)
+{
+    b_info->rdm.type = LIBXL_RDM_RESERVE_TYPE_NONE;

Based on our previous discussion, I will initial this firstly,

+libxl_rdm_reserve_type = Enumeration("rdm_reserve_type", [
+    (0, "none"),
+    (1, "host"),
+    ], init_val = "LIBXL_RDM_RESERVE_TYPE_NONE")
+

and then, I would remove this line since right now we just own two options,
"none" or "host". And both they're fine.

+    b_info->rdm.reserve = LIBXL_RDM_RESERVE_FLAG_RELAXED;

No, not like this. You set everything back to none and relaxed even if
it is set before this point.

It should be
     if (xxx == DEFAULT_SENTINEL_VALUE)
         xxx = THE_DEFAULT_YOU_WANT;

Have a look at libxl__device_nic_setdefault etc to get an idea
how it works. Don't hesitate to ask if I'm not clear enough.

But indeed, here we should set rdm.reserve as you said,

+void libxl__rdm_setdefault(libxl__gc *gc, libxl_domain_build_info *b_info)
+{
+    if (b_info->rdm.reserve == LIBXL_RDM_RESERVE_FLAG_INVALID)
+        b_info->rdm.reserve = LIBXL_RDM_RESERVE_FLAG_RELAXED;
+}
+


Yes. This is fine.

Wei.


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