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Re: [Xen-devel] Reducing or removing direct map from xen (was Re: Ongoing/future speculative mitigation work)
- To: "Wei Liu" <wei.liu2@xxxxxxxxxx>
- From: "Jan Beulich" <JBeulich@xxxxxxxx>
- Date: Fri, 22 Feb 2019 04:48:09 -0700
- Cc: Martin Pohlack <mpohlack@xxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Joao Martins <joao.m.martins@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Mihai Dontu <mdontu@xxxxxxxxxxxxxxx>, Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Anthony Liguori <aliguori@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, uwed@xxxxxxxxx, Lars Kurth <lars.kurth@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Ross Philipson <ross.philipson@xxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Matt Wilson <msw@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Daniel Kiper <daniel.kiper@xxxxxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 22 Feb 2019 11:48:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
>>> 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?
Jan
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