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

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Date:   Mon, 15 Jul 2019 15:44:45 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Christoph Hellwig <hch@....de>, Halil Pasic <pasic@...ux.ibm.com>
CC:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...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>,
        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>
Subject: Re: [PATCH 3/3] fs/core/vmcore: Move sev_active() reference to x86
 arch code

On 7/15/19 9:30 AM, Christoph Hellwig wrote:
> On Mon, Jul 15, 2019 at 04:03:17PM +0200, Halil Pasic wrote:
>>> I thought about that but couldn't put my finger on a general concept.
>>> Is it "guest with memory inaccessible to the host"?
>>>
>>
>> Well, force_dma_unencrypted() is a much better name thatn sev_active():
>> s390 has no AMD SEV, that is sure, but for virtio to work we do need to
>> make our dma accessible to the hypervisor. Yes, your "guest with memory
>> inaccessible to the host" shows into the right direction IMHO.
>> Unfortunately I don't have too many cycles to spend on this right now.
> 
> In x86 it means that we need to remove dma encryption using
> set_memory_decrypted before using it for DMA purposes.  In the SEV
> case that seems to be so that the hypervisor can access it, in the SME
> case that Tom just fixes it is because there is an encrypted bit set
> in the physical address, and if the device doesn't support a large
> enough DMA address the direct mapping code has to encrypt the pages
> used for the contigous allocation.

Just a correction/clarification...

For SME, when a device doesn't support a large enough DMA address to
accommodate the encryption bit as part of the DMA address, the direct
mapping code has to provide un-encrypted pages. For un-encrypted pages,
the DMA address now does not include the encryption bit, making it
acceptable to the device. Since the device is now using a DMA address
without the encryption bit, the physical address in the CPU page table
must match (the call to set_memory_decrypted) so that both the device and
the CPU interact in the same way with the memory.

Thanks,
Tom

> 
>> Being on cc for your patch made me realize that things got broken on
>> s390. Thanks! I've sent out a patch that fixes protvirt, but we are going
>> to benefit from your cleanups. I think with your cleanups and that patch
>> of mine both sev_active() and sme_active() can be removed. Feel free to
>> do so. If not, I can attend to it as well.
> 
> Yes, I think with the dma-mapping fix and this series sme_active and
> sev_active should be gone from common code.  We should also be able
> to remove the exports x86 has for them.
> 
> I'll wait a few days and will then feed the dma-mapping fix to Linus,
> it might make sense to either rebase Thiagos series on top of the
> dma-mapping for-next branch, or wait a few days before reposting.
>