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Re: [Xen-devel] [PATCH v4 0/7] unsafe big.LITTLE support



Hi Peng,

On 09/03/18 09:05, Peng Fan wrote:
On Thu, Mar 08, 2018 at 03:13:50PM +0000, Julien Grall wrote:
On 08/03/18 12:43, Peng Fan wrote:
There are a major difference between Dom0 and DomU in your setup.
Dom0 vCPUs are pinned to a specific pCPU, so they can't move around.
For DomU, each vCPU are pinned to a set of pCPUs, so they can move
around.

But, did you check the DomU has the workaround enabled? I am asking
that because it looks like to me the way to detect the workaround is
based on a device (scu) and not processor. So I am not convinced that
DomU is actually using your workaround.

Just checked this. Because xen toolstack create device tree
with compatible "compatible = "xen,xenvm-4.10", "xen,xenvm";",
but the linux code use "fsl,imx8qm" to detect soc, then call scu
to get revision of chip.

But how does the guest call the scu?


After add an entry in linux side "{ .compatible = "xen,xenvm", .data = 
&imx8qm_soc_data, },"
It seems works. Passed a map/unmap stress test which easily fail without
the tlb workaround.

Wonder is it ok to specific machine compatible in domu.cfg and let xen stack
use this machine compatible other than "xen,xenvm"? Is this acceptable by 
community?

A user should be able to boot a guest safely on any machine without having to hack the configuration file. He should also be able to boot a guest with both ACPI and DT as this is independent from the real machine. So for me the way to find the workaround at the moment is not acceptable for a Xen guest upstream.

What could be acceptable for the community is one of the 3 solutions below:
        1) Only use one of the 2 clusters
        2) Restrict both Xen and Guest to use only 36-bit VA.
3) Trap all TLBs access from the guest and convert them to TLB alle1s/vmalls12e1is

I would be happy to consider any other.

Cheers,

--
Julien Grall

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