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Subject: Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call
 handler
To: Segher Boessenkool <segher@kernel.crashing.org>,
 Michael Ellerman <mpe@ellerman.id.au>
References: <20190808040555.2371-1-cclaudio@linux.ibm.com>
 <20190808040555.2371-3-cclaudio@linux.ibm.com>
 <87wofgqb2g.fsf@concordia.ellerman.id.au>
 <20190814183432.GG31406@gate.crashing.org>
From: Claudio Carvalho <cclaudio@linux.ibm.com>
Message-ID: <dbfbea49-c6b4-6bac-955d-8da03642db47@linux.ibm.com>
Date: Wed, 21 Aug 2019 22:26:39 -0300
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Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
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 linuxppc-dev@ozlabs.org, Ryan Grimm <grimm@linux.ibm.com>,
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On 8/14/19 3:34 PM, Segher Boessenkool wrote:
> 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).

Thanks Segher. We are working on that in the ultravisor source code.

Claudio.


>
>> 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
>

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Claudio Carvalho <cclaudio@linux.ibm.com>
Date: Thu, 22 Aug 2019 01:26:39 +0000
Subject: Re: [PATCH v5 2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
Message-Id: <dbfbea49-c6b4-6bac-955d-8da03642db47@linux.ibm.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20190808040555.2371-1-cclaudio@linux.ibm.com>
 <20190808040555.2371-3-cclaudio@linux.ibm.com>
 <87wofgqb2g.fsf@concordia.ellerman.id.au>
 <20190814183432.GG31406@gate.crashing.org>
In-Reply-To: <20190814183432.GG31406@gate.crashing.org>
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To: Segher Boessenkool <segher@kernel.crashing.org>, 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>, 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>

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