Re: [Xen-devel] [PATCH 3/3] tools/libxc: retry hypercall in case of EFAULT

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Juergen Gross writes ("[PATCH 3/3] tools/libxc: retry hypercall in case of 
EFAULT"):
> A hypercall issued via the privcmd driver can very rarely return
> -EFAULT even if the hypercall buffers are locked in memory. This
> happens for hypercall buffers in user memory when the Linux kernel
> is doing memory scans e.g. for page migration or compaction.
> 
> Retry the getpageframeinfo3 hypercall up to 2 times in case
> -EFAULT is returned and the hypervisor might see invalid PTEs for
> user hypercall buffers.

It would be worth mentioning in the commit message that this is a
workaround for systems without privcmd-buf, which does not have this
bug.  But nevertheless:

Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

Overall, thanks for chasing up this long-standing bug.

Thanks,
Ian.

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