Re: [v4 0/8] Add VT-d Posted-Interrupts support - IOMMU part

From: Li, ZhenHua
Date: Fri Apr 03 2015 - 04:13:45 EST


Hi Feng Wu,
In my patchset, I created a new member ir_table->base_old_phys; In the normal kernel, everything is the same. In kdump kernel, ir_table->base is used for a buffer, and ir_table->base_old_phys is the physical address of the tables used by the old kernel, also being used by the current kernel.

I did this in modify_irte():

set_64bit(&irte->high, irte_modified->high);
+
+#ifdef CONFIG_CRASH_DUMP
+ if (is_kdump_kernel())
+ __iommu_update_old_irte(iommu, index);
+#endif
__iommu_flush_cache(iommu, irte, sizeof(*irte));


Here the irte tables are stored in two places:
iommu->ir_table->base : It is a buffer in kdump kernel, which is the running kernel;
iommu->ir_table->base_old_phys : It is the irte used by the old kernel;

And function __iommu_update_old_irte is used to save the content of iommu->ir_table->base to iommu->ir_table->base_old_phys. Because in kdump kernel, the vt-d is using ir_table->base_old_phys, not ir_table->base, so we need to copy the updated ir_table->base to ir_table->base_old_phys .


Thanks
Zhenhua

On 04/02/2015 07:28 PM, Joerg Roedel wrote:
On Mon, Feb 02, 2015 at 04:06:56PM +0800, Feng Wu wrote:
VT-d Posted-Interrupts is an enhancement to CPU side Posted-Interrupt.
With VT-d Posted-Interrupts enabled, external interrupts from
direct-assigned devices can be delivered to guests without VMM
intervention when guest is running in non-root mode.

You can find the VT-d Posted-Interrtups Spec. in the following URL:
http://www.intel.com/content/www/us/en/intelligent-systems/intel-technology/vt-directed-io-spec.html

This series was part of http://thread.gmane.org/gmane.linux.kernel.iommu/7708. To make things clear, send out IOMMU part here.

Besides the modify_irte() changes I asked for the patch-set looks good.
I just have some concerns what these changes mean for the VT-d kdump
improvements Zhen-Hua Li is working on. Can you please discuss the
implications of having both patch-sets applied with him and make sure
they work together? I think in its current form your patch-set breaks
the kdump support patches. I added Zhen-Hua to Cc.

Thanks,

Joerg


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