Re: [XEN PATCH v1 1/1] x86/domctl: add gva_to_gfn command

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Mar 20, 2023 at 12:32 PM Ковалёв Сергей <valor@xxxxxxx> wrote:
>
> gva_to_gfn command used for fast address translation in LibVMI project.
> With such a command it is possible to perform address translation in
> single call instead of series of queries to get every page table.

You have a couple assumptions here:

 - Xen will always have a direct map of the entire guest memory - there are already plans to move away from that. Without that this approach won't have any advantage over doing the same mapping by LibVMI

 - LibVMI has to map every page for each page table for every lookup - you have to do that only for the first, afterwards the pages on which the pagetable is are kept in a cache and subsequent lookups would be actually faster then having to do this domctl since you can keep being in the same process instead of having to jump to Xen.

With these perspectives in mind I don't think this would be a useful addition. Please prove me wrong with performance numbers and a specific use-case that warrants adding this and how you plan to introduce it into LibVMI without causing performance regression to all other use-cases.

Tamas