Re: [PATCH v6 00/17] x86: Secure Encrypted Virtualization (AMD)

[Brijesh Singh <brijesh.singh@amd.com>]

On 5/29/17 3:38 PM, Jordan Justen wrote:
> On 2017-05-29 04:16:15, Laszlo Ersek wrote:
>> (looks like I was the one to comment as second reviewer after all :) )
>>
>> On 05/26/17 23:05, Jordan Justen wrote:
>>> On 2017-05-26 07:43:48, Brijesh Singh wrote:
>>>> Changes since v4:
>>>>  - decouple IoMmu protocol implementation from AmdSevDxe into a seperate
>>>>    IoMmuDxe driver. And introduce a placeholder protocol to provide the
>>>>    dependency support for the dependent modules.
>>> I think you split IoMmuDxe out from AmdSevDxe based on my feedback
>>> regarding APRIORI, but I don't think this helped.
>>>
>>> Ideally I would like to see one driver named IoMmuDxe that is *not* in
>>> APRIORI.
>> There are two separate goals here:
>>
>> (1) Make sure that any driver that adds MMIO ranges will automatically
>> add those ranges with the C bit cleared in the PTEs, without actually
>> knowing about SEV.
> Ok, this sounds reasonable.
>
> The APRIORI method looks like a hack. Why is this not being handled at
> the time the page tables are being built, in DxeIpl? Couldn't we
> define a platform Page Tables library to allow a platform to somehow
> modify the page tables as they are built? Or, maybe just after? This
> would also make sure it happens before DXE runs.

Before introducing  AmdSevDxe driver, we did proposed patches to clear
the C-bit during the page table creation time. In the first patch [1],
Leo tried to  teach gcd.c to clear the C-bit from MMIO. IIRC, the main
concern was -- typically Dxecore does not do any CPU specific thing
hence we should try to find some alternative approach. In second patch
[2], Leo tried to introduce a new notify protocol to get MMIO add/remove
events. During discussion Jiewen suggested to look into adding a new
platform driver into APRIORI to avoid the need for any modifications
inside the Gcdcore - this seems workable solution which did not require
adding any CPU specific code inside the Gcd.

[1] https://lists.01.org/pipermail/edk2-devel/2017-March/008974.html
[2] https://lists.01.org/pipermail/edk2-devel/2017-April/009852.html