From: Scott Wood <scottwood@freescale.com>
To: Bhushan Bharat-R65777 <R65777@freescale.com>
Cc: Wood Scott-B07421 <B07421@freescale.com>,
Michael Neuling <mikey@neuling.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: BOOKE KVM calling load_up_fpu from C?
Date: Tue, 12 Feb 2013 19:23:14 -0600 [thread overview]
Message-ID: <1360718594.24612.21@snotra> (raw)
In-Reply-To: <6A3DF150A5B70D4F9B66A25E3F7C888D065A3456@039-SN2MPN1-023.039d.mgd.msft.net> (from R65777@freescale.com on Tue Feb 12 19:18:14 2013)
On 02/12/2013 07:18:14 PM, Bhushan Bharat-R65777 wrote:
>=20
>=20
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, February 13, 2013 12:03 AM
> > To: Bhushan Bharat-R65777
> > Cc: Michael Neuling; Wood Scott-B07421; =20
> linuxppc-dev@lists.ozlabs.org
> > Subject: Re: BOOKE KVM calling load_up_fpu from C?
> >
> > On 02/12/2013 03:01:07 AM, Bhushan Bharat-R65777 wrote:
> > > To me this looks wrong. And this seems to works because the
> > > thread->reg->msr is not actually used to write SRR1 (and =20
> eventually
> > > the thread MSR) when doing rfi to enter guest. Infact
> > > Guest(shadow_msr) MSR is used as SRR1 and which will have proper =20
> MSR
> > > (including FP set).
> > >
> > > But Yes, Scott is right person to comment, So let us wait for him
> > > comment.
> >
> > I don't think it's actually a problem on 32-bit, since r9 is =20
> modified but never
> > actually used for anything.
>=20
> Is not the epilog loads srr1 in r9 and load_up_fpu() changes r9 and =20
> then r9 is written back in srr1 ?
What epilog? We're talking about the case where it's called from C =20
code.
When it's called from an exception handler, then r9 is used, but in =20
that case it's also initialized before calling load_up_fpu, by the =20
prolog.
> > On 64-bit, though, there's a store to the caller's
> > stack frame (yuck) which the kvm/booke.h caller is not prepared for.
>=20
> So if caller is using r12 then it can lead to come corruption, right ?
No, r12 is a volatile register in the ABI, as is r9. The issue is that =20
the stack can be corrupted.
-Scott=
next prev parent reply other threads:[~2013-02-13 1:23 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-12 3:29 BOOKE KVM calling load_up_fpu from C? Michael Neuling
2013-02-12 3:37 ` Bhushan Bharat-R65777
2013-02-12 3:46 ` Michael Neuling
2013-02-12 3:58 ` Bhushan Bharat-R65777
2013-02-12 4:16 ` Michael Neuling
2013-02-12 9:01 ` Bhushan Bharat-R65777
2013-02-12 18:33 ` Scott Wood
2013-02-12 22:51 ` Michael Neuling
2013-02-13 1:18 ` Bhushan Bharat-R65777
2013-02-13 1:23 ` Scott Wood [this message]
2013-02-13 1:26 ` Bhushan Bharat-R65777
2013-02-13 4:17 ` Bhushan Bharat-R65777
2013-02-13 17:37 ` Scott Wood
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