From: David Woodhouse <dwmw2@infradead.org>
To: andrew.cooper3@citrix.com
Cc: George.Dunlap@eu.citrix.com, jbeulich@suse.com, julien@xen.org,
roger.pau@citrix.com, sstabellini@kernel.org, wl@xen.org,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH] x86/sm{e, a}p: do not enable SMEP/SMAP in PV shim by default on AMD
Date: Thu, 12 Oct 2023 09:21:16 +0100 [thread overview]
Message-ID: <26fd7f099ab39ffccc2a5db8b4224fac6806461e.camel@infradead.org> (raw)
In-Reply-To: <b978a111-4cfb-45f3-850a-a5051298abef@citrix.com>
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On Thu, 2023-10-12 at 10:13 +0800, andrew.cooper3@citrix.com wrote:
> On 11/10/2023 7:34 pm, David Woodhouse wrote:
> > But why does the shim even need to turn it off when switching to the
> > guest context? Its guest isn't running in supervisor mode so surely it
> > doesn't *matter* whether SMEP is enabled or not? Why not just leave it
> > on at all times?
>
> 32bit PV kernels run in Ring1. Which is supervisor and not user.
Ah, thanks.
> Some older PV kernels do execute on user pages, and don't like getting
> SMEP faults when they didn't turn it on to begin with.
PV guests never actually had the option to turn SMEP on, did they?
(Otherwise I may have to rethink the approach of just putting
'smep=off' onto the shim command line when running under KVM...)
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next prev parent reply other threads:[~2023-10-12 8:21 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 16:00 [Xen-devel] [PATCH] x86/sm{e, a}p: do not enable SMEP/SMAP in PV shim by default on AMD Igor Druzhinin
2020-01-16 16:16 ` Andrew Cooper
2023-10-11 11:34 ` David Woodhouse
2023-10-12 2:13 ` andrew.cooper3
2023-10-12 8:21 ` David Woodhouse [this message]
2023-10-12 8:33 ` Andrew Cooper
2020-01-17 11:10 ` Jan Beulich
2020-01-20 14:07 ` Roger Pau Monné
2020-01-20 14:38 ` Jan Beulich
2020-01-20 15:37 ` Roger Pau Monné
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