linux-kernel - Re: [PATCH 3/3] fs/core/vmcore: Move sev

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Date:   Fri, 12 Jul 2019 18:55:47 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     x86@...nel.org, iommu@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>,
        "Lendacky\, Thomas" <thomas.lendacky@....com>
Subject: Re: [PATCH 3/3] fs/core/vmcore: Move sev_active() reference to x86 arch code

[ Cc'ing Tom Lendacky which I forgot to do earlier. Sorry about that. ]

Hello Halil,

Thanks for the quick review.

Halil Pasic <pasic@...ux.ibm.com> writes:

> On Fri, 12 Jul 2019 02:36:31 -0300
> Thiago Jung Bauermann <bauerman@...ux.ibm.com> wrote:
>
>> Secure Encrypted Virtualization is an x86-specific feature, so it shouldn't
>> appear in generic kernel code because it forces non-x86 architectures to
>> define the sev_active() function, which doesn't make a lot of sense.
>
> sev_active() might be just bad (too specific) name for a general
> concept. s390 code defines it drives the right behavior in
> kernel/dma/direct.c (which uses it).

I thought about that but couldn't put my finger on a general concept.
Is it "guest with memory inaccessible to the host"?

Since your proposed definiton for force_dma_unencrypted() is simply to
make it equivalent to sev_active(), I thought it was more
straightforward to make each arch define force_dma_unencrypted()
directly.

Also, does sev_active() drive the right behavior for s390 in
elfcorehdr_read() as well?

>> To solve this problem, add an x86 elfcorehdr_read() function to override
>> the generic weak implementation. To do that, it's necessary to make
>> read_from_oldmem() public so that it can be used outside of vmcore.c.
>>
>> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
>> ---
>>  arch/x86/kernel/crash_dump_64.c |  5 +++++
>>  fs/proc/vmcore.c                |  8 ++++----
>>  include/linux/crash_dump.h      | 14 ++++++++++++++
>>  include/linux/mem_encrypt.h     |  1 -
>>  4 files changed, 23 insertions(+), 5 deletions(-)
>
> Does not seem to apply to today's or yesterdays master.

It assumes the presence of the two patches I mentioned in the cover
letter. Only one of them is in master.

I hadn't realized the s390 virtio patches were on their way to upstream.
I was keeping an eye on the email thread but didn't see they were picked
up in the s390 pull request. I'll add a new patch to this series making
the corresponding changes to s390's <asm/mem_encrypt.h> as well.

--
Thiago Jung Bauermann
IBM Linux Technology Center