linux-kernel - Re: [PATCH v3 08/16] powerpc/pseries/svm: Use shared memory for LPPACA structures

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Date:   Thu, 15 Aug 2019 21:52:17 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: Re: [PATCH v3 08/16] powerpc/pseries/svm: Use shared memory for LPPACA structures


Michael Ellerman <mpe@...erman.id.au> writes:

> Thiago Jung Bauermann <bauerman@...ux.ibm.com> writes:
>> Michael Ellerman <mpe@...erman.id.au> writes:
>>> Thiago Jung Bauermann <bauerman@...ux.ibm.com> writes:
>>>> From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
>>>>
>>>> LPPACA structures need to be shared with the host. Hence they need to be in
>>>> shared memory. Instead of allocating individual chunks of memory for a
>>>> given structure from memblock, a contiguous chunk of memory is allocated
>>>> and then converted into shared memory. Subsequent allocation requests will
>>>> come from the contiguous chunk which will be always shared memory for all
>>>> structures.
>>>>
>>>> While we are able to use a kmem_cache constructor for the Debug Trace Log,
>>>> LPPACAs are allocated very early in the boot process (before SLUB is
>>>> available) so we need to use a simpler scheme here.
>>>>
>>>> Introduce helper is_svm_platform() which uses the S bit of the MSR to tell
>>>> whether we're running as a secure guest.
>>>>
>>>> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
>>>> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
>>>> ---
>>>>  arch/powerpc/include/asm/svm.h | 26 ++++++++++++++++++++
>>>>  arch/powerpc/kernel/paca.c     | 43 +++++++++++++++++++++++++++++++++-
>>>>  2 files changed, 68 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/powerpc/include/asm/svm.h b/arch/powerpc/include/asm/svm.h
>>>> new file mode 100644
>>>> index 000000000000..fef3740f46a6
>>>> --- /dev/null
>>>> +++ b/arch/powerpc/include/asm/svm.h
>>>> @@ -0,0 +1,26 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>>> +/*
>>>> + * SVM helper functions
>>>> + *
>>>> + * Copyright 2019 Anshuman Khandual, IBM Corporation.
>>>
>>> Are we sure this copyright date is correct?
>>
>> I may be confused about which year the copyright refers to. I thought it
>> was the year when the patch was committed. If it is the first time the
>> patch was published then this one should be 2018.
>
> I'm not a lawyer etc. but AIUI the date above is about the authorship,
> ie. when it was originally written, not when it was published or
> committed.
>
> In general I don't think it matters too much, but in this case I'm
> pretty sure Anshuman can't have possibly written it in 2019 on behalf of
> IBM :)
>
> So we can either change the date to 2018, or drop his name and just say
> it's copyright 2019 by IBM.

I think it's better to change the date to 2018. The same should be done
for svm.c, svm.h and mem_encrypt.h. I'll send a new patch series with
the correction.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center