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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

On 11/05/17 15:38, Oleksandr Tyshchenko wrote:
On Thu, May 11, 2017 at 2:28 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
Hi Oleksandr,
Hi Julien

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 *dev,

        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;
I got it for SMMU.

But, for IPMMU we will override since iommu_hap_pt_share is true by
default. Right?

* The IPMMU can't reuse P2M table since it only supports
* stage-1 page tables.
iommu_hap_pt_share = false;

Good point. Looking at the other driver, they print a message to notify the override. (See drivers/passthrough/amd/iommu_init.c for instance).


Julien Grall

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