Re: [PATCH v9 07/10] iommu/vt-d: enable kdump support in iommu module

From: Li, ZhenHua
Date: Fri Apr 03 2015 - 03:46:23 EST

Hi Joerg,
Thinking about it carefully, I think you suggestions are very helpful, and the checks should be:
* All these things should be done in the second kernel, not only the kdump kernel. Sometimes user may use kexec manually start a new kernel.
* Copying those tables should only happen in the second kernel, only in this situation: iommu is enabled in both first and second kernel.

So, I think we can do this:
1. Use a new variable iommu_enabled_in_last_kernel;
2. When iommu module is loaded, it means the iommu is enabled in current kernel. Then we check DMA_GSTS_TES:
* if DMA_GSTS_TES is set, then it should be the second kernel(kexec starts this kernel manually, or it is kdump kernel), and the first kernel used iommu tables. Here we need to copy these tables; then set iommu_enabled_in_last_kernel to 1.
* if DMA_GSTS_TES is NOT set, then we do not need to care about these tables.

3. Replace all
if (is_kdump_kernel()) {
// Do some thing

if (iommu_enabled_in_last_kernel) {
// Do some thing

Do you agree with these?


On 04/02/2015 07:06 PM, Joerg Roedel wrote:
On Thu, Mar 19, 2015 at 01:36:25PM +0800, Li, Zhen-Hua wrote:
+ if (is_kdump_kernel())
+ __iommu_update_old_root_entry(iommu, bus);

All the is_kdump_kernel checks in this patch (and maybe in other patches
too) should really be checks whether translation on the IOMMU was
enabled or not when the kernel booted. You might also boot from a kernel
that had translation disabled into a kdump kernel that wants to enable
it. In this case these checks would break.

Speaking of booting from kernels with translation disabled, there is a
valid use of is_kdump_enabled(), to omit iommu initialization in the
kdump kernel when translation was disabled before. But the other checks
should depend on the state the iommu had when booting the kdump kernel.


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