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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 18:34:32 +0000	[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

WARNING: multiple messages have this Message-ID (diff)
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

  reply	other threads:[~2019-08-14 18:34 UTC|newest]

Thread overview: 40+ 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 ` Claudio Carvalho
2019-08-08  4:05 ` [PATCH v5 1/7] Documentation/powerpc: Ultravisor API Claudio Carvalho
2019-08-08  4:05   ` Claudio Carvalho
2019-08-09 12:45   ` Michael Ellerman
2019-08-09 12:45     ` Michael Ellerman
2019-08-21 22:30     ` Claudio Carvalho
2019-08-21 22:30       ` Claudio Carvalho
2019-08-12 15:58   ` Fabiano Rosas
2019-08-12 15:58     ` Fabiano Rosas
2019-08-21 22:01     ` Claudio Carvalho
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
2019-08-08  4:05   ` Claudio Carvalho
2019-08-14 10:46   ` Michael Ellerman
2019-08-14 10:46     ` Michael Ellerman
2019-08-14 18:34     ` Segher Boessenkool [this message]
2019-08-14 18:34       ` Segher Boessenkool
2019-08-22  1:26       ` Claudio Carvalho
2019-08-22  1:26         ` Claudio Carvalho
2019-08-22  1:24     ` 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   ` Claudio Carvalho
2019-08-08  4:05 ` [PATCH v5 4/7] powerpc/mm: Use UV_WRITE_PATE ucall to register a PATE Claudio Carvalho
2019-08-08  4:05   ` Claudio Carvalho
2019-08-14 11:33   ` Michael Ellerman
2019-08-14 11:33     ` Michael Ellerman
2019-08-21  0:04     ` Sukadev Bhattiprolu
2019-08-21  0:04       ` Sukadev Bhattiprolu
2019-08-22  1:33     ` Claudio Carvalho
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
2019-08-08  4:05   ` Claudio Carvalho
2019-08-14 12:04   ` Michael Ellerman
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   ` Claudio Carvalho
2019-08-08  4:05 ` [PATCH v5 7/7] powerpc/kvm: Use UV_RETURN ucall to return to ultravisor Claudio Carvalho
2019-08-08  4:05   ` Claudio Carvalho

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