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Re: [Xen-devel] Reducing or removing direct map from xen (was Re: Ongoing/future speculative mitigation work)

On Wed, Feb 20, 2019 at 05:08:09PM +0000, Wei Liu wrote:
> On Wed, Feb 20, 2019 at 01:09:56PM +0000, Wei Liu wrote:
> [...]
> > I think under-allocate-then-map looks plausible. xmalloc will need
> > to allocate pages, put them into an array and call __vmap on that array
> > directly.
> The biggest issue with this approach is that we now need an array of
> 1UL<<MAX_ORDER to accommodate mfns. Back of envelope calculation: on x86
> this is going to be (1UL<<20)*8 bytes long. This is not feasible.

Right. I guess the only remaining option is to allocate a virtual
address space and populate it using multiple pages?

That would likely require to split some functions into smaller helpers
so you can call them and provide the virtual address where a page
should be mapped?


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