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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Feb 22, 2019 at 04:48:09AM -0700, Jan Beulich wrote:
> >>> On 20.02.19 at 18:08, <wei.liu2@xxxxxxxxxx> 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.
> 
> Are we really calling xmalloc() with any number nearly this big?

In practice, I don't think so. What do you think is a sensible limit?

Wei.

> 
> Jan
> 
> 

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