Re: [Xen-devel] Ongoing/future speculative mitigation work

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.12.18 at 19:05, <wei.liu2@xxxxxxxxxx> wrote:
> On Fri, Oct 26, 2018 at 05:20:47AM -0600, Jan Beulich wrote:
>> >>> On 26.10.18 at 12:51, <george.dunlap@xxxxxxxxxx> wrote:
>> > The basic solution involves having a xenheap virtual address mapping
>> > area not tied to the physical layout of the memory.  domheap and xenheap
>> > memory would have to come from the same pool, but xenheap would need to
>> > be mapped into the xenheap virtual memory region before being returned.
>> 
>> Wouldn't this most easily be done by making alloc_xenheap_pages()
>> call alloc_domheap_pages() and then vmap() the result? Of course
>> we may need to grow the vmap area in that case.
> 
> The existing vmap area is 64GB, but that should be big enough for Xen?

In the common case perhaps. But what about extreme cases, like
very many VMs on multi-Tb hosts?

> If that's not big enough, we need to move that area to a different
> location, because it can't expand to either side of the address space.

When the directmap goes away, ample address space gets freed
up.

Jan



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