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SubjectRe: [RFC PATCH] x86-32: Start out eflags and cr4 clean
On Tue, Sep 25, 2012 at 02:48:20PM +0100, Ian Campbell wrote:
> On Tue, 2012-09-25 at 00:27 +0100, H. Peter Anvin wrote:
> > From: "H. Peter Anvin" <hpa@linux.intel.com>
> >
> > %cr4 is supposed to reflect a set of features into which the operating
> > system is opting in. If the BIOS or bootloader leaks bits here, this
> > is not desirable. Consider a bootloader passing in %cr4.pae set to a
> > legacy paging kernel, for example -- it will not have any immediate
> > effect, but the kernel would crash when turning paging on.
> >
> > A similar argument applies to %eflags, and since we have to look for
> > %eflags.id being settable we can use a sequence which clears %eflags
> > as a side effect.
> >
> > Note that we already do this for x86-64.
> >
> > I would like opinions on this especially from the PV crowd
>
> Xen PV guests don't pass through this code path so there is no danger
> there AFAICT, so from that PoV:
>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
>
> FWIW it looks correct to me from the native PoV too, but you probably
> already knew that ;-)

And sanity testing confirmed it.

Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>
> Ian.
>
>
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