From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
Michael Anderson <andmike@linux.ibm.com>,
Ram Pai <linuxram@us.ibm.com>,
Claudio Carvalho <cclaudio@linux.ibm.com>,
kvm-ppc@vger.kernel.org, Bharata B Rao <bharata@linux.ibm.com>,
linuxppc-dev@ozlabs.org, Ryan Grimm <grimm@linux.ibm.com>,
Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
Guerney Hunt <gdhh@linux.ibm.com>,
Thiago Bauermann <bauerman@linux.ibm.com>
Subject: Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
Date: Wed, 14 Aug 2019 13:34:32 -0500 [thread overview]
Message-ID: <20190814183432.GG31406@gate.crashing.org> (raw)
In-Reply-To: <87wofgqb2g.fsf@concordia.ellerman.id.au>
On Wed, Aug 14, 2019 at 08:46:15PM +1000, Michael Ellerman wrote:
> Claudio Carvalho <cclaudio@linux.ibm.com> writes:
> > +_GLOBAL(ucall_norets)
> > +EXPORT_SYMBOL_GPL(ucall_norets)
> > + mfcr r0
> > + stw r0,8(r1)
> > +
> > + sc 2 /* Invoke the ultravisor */
> > +
> > + lwz r0,8(r1)
> > + mtcrf 0xff,r0
> > + blr /* Return r3 = status */
>
> Paulus points that we shouldn't need to save CR here. Our caller will
> have already saved it if it needed to, and we don't use CR in this
> function so we don't need to save it.
>
> That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are
> non-volatile (PAPR § 14.5.3).
And assuming the ultravisor already clears (or sets, or whatever) all CR
fields it does not want to leak the contents of (which it also should,
of course).
> I know plpar_hcall_norets() does save CR, but it shouldn't need to, that
> seems to be historical. aka. no one knows why it does it but it always
> has.
Segher
next prev parent reply other threads:[~2019-08-14 18:36 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-08 4:05 [PATCH v5 0/7] kvmppc: Paravirtualize KVM to support ultravisor Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 1/7] Documentation/powerpc: Ultravisor API Claudio Carvalho
2019-08-09 12:45 ` Michael Ellerman
2019-08-21 22:30 ` Claudio Carvalho
2019-08-12 15:58 ` Fabiano Rosas
2019-08-21 22:01 ` Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler Claudio Carvalho
2019-08-14 10:46 ` Michael Ellerman
2019-08-14 18:34 ` Segher Boessenkool [this message]
2019-08-22 1:26 ` Claudio Carvalho
2019-08-22 1:24 ` Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 3/7] powerpc/powernv: Introduce FW_FEATURE_ULTRAVISOR Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 4/7] powerpc/mm: Use UV_WRITE_PATE ucall to register a PATE Claudio Carvalho
2019-08-14 11:33 ` Michael Ellerman
2019-08-21 0:04 ` Sukadev Bhattiprolu
2019-08-22 1:33 ` Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 5/7] powerpc/mm: Write to PTCR only if ultravisor disabled Claudio Carvalho
2019-08-14 12:04 ` Michael Ellerman
2019-08-08 4:05 ` [PATCH v5 6/7] powerpc/powernv: Access LDBAR " Claudio Carvalho
2019-08-08 4:05 ` [PATCH v5 7/7] powerpc/kvm: Use UV_RETURN ucall to return to ultravisor Claudio Carvalho
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