linux-kernel - Re: [PATCH 30/30] x86, kaiser, xen: Dynamically disable KAISER when running under Xen PV

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Date:   Thu, 9 Nov 2017 16:01:42 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, moritz.lipp@...k.tugraz.at,
        daniel.gruss@...k.tugraz.at, michael.schwarz@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at, luto@...nel.org,
        torvalds@...ux-foundation.org, keescook@...gle.com,
        hughd@...gle.com, x86@...nel.org
Subject: Re: [PATCH 30/30] x86, kaiser, xen: Dynamically disable KAISER when
 running under Xen PV

On 08/11/17 20:47, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> If you paravirtualize the MMU, you can not use KAISER.  This boils down
> to the fact that KAISER needs to do CR3 writes in places that it is not
> feasible to do real hypercalls.
> 
> If we detect that Xen PV is in use, do not do the KAISER CR3 switches.
> 
> I don't think this too bug of a deal for Xen.  I was under the
> impression that the Xen guest kernel and Xen guest userspace didn't
> share an address space *anyway* so Xen PV is not normally even exposed
> to the kinds of things that KAISER protects against.
> 
> This allows KAISER=y kernels to deployed in environments that also
> require PARAVIRT=y.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

Acked-by: Juergen Gross <jgross@...e.com>


Juergen