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Re: [Xen-devel] [PATCH v1 05/10] iommu/arm: Re-define iommu_use_hap_pt(d) as iommu_hap_pt_share

Hi Oleksandr,

On 10/05/17 15:03, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Not every integrated into ARM SoCs IOMMU can share page tables
with the CPU and as result the iommu_use_hap_pt(d) is not always true.
Reuse x86's iommu_hap_pt_share flag to indicate whether the IOMMU
page table is shared or not.

Now all IOMMU drivers on ARM are able to change this flag
according to their possibilities like x86-variants do.
Therefore set iommu_hap_pt_share flag for SMMU because it always shares
page table with the CPU.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
 xen/drivers/passthrough/arm/smmu.c | 3 +++
 xen/include/asm-arm/iommu.h        | 7 +++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
index 527a592..86ee12a 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -2870,6 +2870,9 @@ static __init int arm_smmu_dt_init(struct dt_device_node 

        platform_features &= smmu->features;

+       /* Always share P2M table between the CPU and the SMMU */
+       iommu_hap_pt_share = true;

I would prefer to bail-out if someone try to unshare the page-table rather than overriding. This would help us to know if someone are try to do that.

So I would do:

if ( !iommu_hap_pt_share )
        return -EINVAL;

        return 0;

diff --git a/xen/include/asm-arm/iommu.h b/xen/include/asm-arm/iommu.h
index 57d9b1e..10a6f23 100644
--- a/xen/include/asm-arm/iommu.h
+++ b/xen/include/asm-arm/iommu.h
@@ -20,8 +20,11 @@ struct arch_iommu
     void *priv;

-/* Always share P2M Table between the CPU and the IOMMU */
-#define iommu_use_hap_pt(d) (1)
+ * The ARM domain always has a P2M table, but not every integrated into
+ * ARM SoCs IOMMU can use it as page table.

The first part: "ARM domain has a P2M table" is pretty obvious. I would instead say: "Not every ARM SoCs IOMMU use the same page-table format as the processor.".

+ */
+#define iommu_use_hap_pt(d) (iommu_hap_pt_share)

 const struct iommu_ops *iommu_get_ops(void);
 void __init iommu_set_ops(const struct iommu_ops *ops);


Julien Grall

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