Re: [Xen-devel] Re: Next steps with pv_ops for Xen

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Derek Murray wrote:
> Ultimately, fork calls dup_mm, which calls, dup_mmap, which calls
> copy_{page,pud,pmd,pte}_range, which calls copy_one_pte, which calls
> set_pte_at, which hypercalls HYPERVISOR_update_va_mapping.
>
> The hypercall will not succeed and will return an error code
> indicating the reason for this. Therefore the PTE will not be set.
> There appears to be no way to propagate this error through the Linux
> VM code, because there is no concept of a PTE update failing. I could
> add return codes to all those functions, but I don't fancy their
> chances upstream....

Could we use one of the software-defined bits in the PTE to indicate
that this is a foreign/granted PTE, and have set_pte_at behave
differently if you pass it a pte with this bit set?

    J

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