linux-kernel - Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG

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Date:   Fri, 17 Mar 2017 12:09:42 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Brijesh Singh <brijesh.singh@....com>, simon.guinot@...uanux.org,
        linux-efi@...r.kernel.org, kvm@...r.kernel.org, rkrcmar@...hat.com,
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Subject: Re: [RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT
 command



On 16/03/2017 19:41, Brijesh Singh wrote:
>>
>> Please do add it, it doesn't seem very different from what you're doing
>> in LAUNCH_UPDATE_DATA.  There's no need for a separate
>> __sev_dbg_decrypt_page function, you can just pin/unpin here and do a
>> per-page loop as in LAUNCH_UPDATE_DATA.
> 
> I can certainly add support to handle crossing the page boundary cases.
> Should we limit the size to prevent user passing arbitrary long length
> and we end up looping inside the kernel? I was thinking to limit to a
> PAGE_SIZE.

I guess it depends on how it's used.  PAGE_SIZE makes sense since you
only know if a physical address is encrypted when you reach it from a
visit of the page tables.

Paolo