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Subject: Re: [PATCH 30/30] x86, kaiser, xen: Dynamically disable KAISER when
 running under Xen PV
To: Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, moritz.lipp@iaik.tugraz.at,
        daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at,
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References: <20171108194646.907A1942@viggo.jf.intel.com>
 <20171108194742.8CD79E09@viggo.jf.intel.com>
From: Juergen Gross <jgross@suse.com>
Message-ID: <7e70274c-6ad0-9f9c-0ad3-8d3306d8174a@suse.com>
Date: Thu, 9 Nov 2017 16:01:42 +0100
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On 08/11/17 20:47, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@linux.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@linux.intel.com>

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


Juergen