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Re: [Xen-devel] [PATCH v7 3/6] iommu: make iommu_inclusive_mapping a suboption of dom0-iommu



Hi,

On 22/08/18 16:22, Roger Pau Monné wrote:
On Wed, Aug 22, 2018 at 04:07:26PM +0100, Julien Grall wrote:
Hi Roger,

On 22/08/18 08:51, Roger Pau Monne wrote:
Introduce a new dom0-iommu=map-inclusive generic option that
supersedes iommu_inclusive_mapping. The previous behavior is preserved
and the option should only be enabled by default on Intel hardware.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
Changes since v4:
   - Use an if to set the default option value.
   - Set the option to false unconditionally on ARM.

Changes since v2:
   - Fix typo in commit message.
   - Change style and text of the documentation in xen command line.
   - Set the defaults in {intel/amd}_iommu_hwdom_init for inclusive.
   - Re-add the iommu_dom0_passthrough || !is_pv_domain(d) check.

Changes since v1:
   - Use dom0-iommu instead of the iommu option.
   - Only enable by default on Intel hardware.
---
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Cc: Brian Woods <brian.woods@xxxxxxx>
Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
---
   docs/misc/xen-command-line.markdown         | 13 ++++-
   xen/drivers/passthrough/amd/pci_amd_iommu.c |  4 ++
   xen/drivers/passthrough/arm/iommu.c         |  4 ++
   xen/drivers/passthrough/arm/smmu.c          |  2 +
   xen/drivers/passthrough/iommu.c             | 12 +++++
   xen/drivers/passthrough/vtd/extern.h        |  2 -
   xen/drivers/passthrough/vtd/iommu.c         |  8 ++-
   xen/drivers/passthrough/vtd/x86/vtd.c       | 58 +-------------------
   xen/drivers/passthrough/x86/iommu.c         | 59 +++++++++++++++++++++
   xen/include/xen/iommu.h                     |  2 +
   10 files changed, 99 insertions(+), 65 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index cd57960ede..98f0f3b68b 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -682,7 +682,7 @@ Flag that makes a dom0 use shadow paging. Only works when 
"pvh" is
   enabled.
   ### dom0-iommu
-> `= List of [ passthrough | strict ]`
+> `= List of [ passthrough | strict | map-inclusive ]`
   This list of booleans controls the iommu usage by Dom0:
@@ -696,6 +696,14 @@ This list of booleans controls the iommu usage by Dom0:
     `true` for a PVH Dom0 and any attempt to overwrite it from the command line
     is ignored.
+* `map-inclusive`: sets up DMA remapping for all the non-RAM regions below 4GB
+  except for unusable ranges. Use this to work around firmware issues providing
+  incorrect RMRR/IVMD entries. Rather than only mapping RAM pages for IOMMU
+  accesses for Dom0, with this option all pages up to 4GB, not marked as
+  unusable in the E820 table, will get a mapping established. Note that this
+  option is only applicable to a PV Dom0 and is enabled by default on Intel
+  hardware.
+
   ### dom0\_ioports\_disable (x86)
   > `= List of <hex>-<hex>`
@@ -1233,6 +1241,9 @@ wait descriptor timed out', try increasing this value.
   ### iommu\_inclusive\_mapping (VT-d)
   > `= <boolean>`
+**WARNING: This command line option is deprecated, and superseded by
+_dom0-iommu=map-inclusive_ - using both options in combination is undefined.**
+
   > Default: `true`
   Use this to work around firmware issues providing incorrect RMRR entries.
diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c 
b/xen/drivers/passthrough/amd/pci_amd_iommu.c
index ab39e7500d..27eb49619d 100644
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -253,6 +253,10 @@ static void __hwdom_init amd_iommu_hwdom_init(struct 
domain *d)
       unsigned long i;
       const struct amd_iommu *iommu;
+    /* Inclusive IOMMU mappings are disabled by default on AMD hardware. */
+    if ( iommu_hwdom_inclusive == -1 )
+        iommu_hwdom_inclusive = false;

This is a quite bad practice to mix boolean and integer. Can you please
rework the code to avoid that?

I don't think I can fix that. An integer is used so that the default
value is set to -1. Then at runtime a default value based on the
hardware is set unless the user has already specified a value on the
command line.

It needs to be a tristate in order to detect whether the user has
specified a value on the command line.

In that case the solution is to use -1, 0, 1. So replacing false with 0 and true with 1.

Cheers,

--
Julien Grall

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