Re: [kvm-unit-tests PATCH 0/6] Initial x86_64 UEFI support

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On 8/19/21 3:32 AM, Marc Orr wrote:
> On Wed, Aug 18, 2021 at 1:38 AM Varad Gautam <varad.gautam@xxxxxxxx> wrote:
>>
>> Hi Marc, Zixuan,
>>
>> On 8/18/21 3:52 AM, Marc Orr wrote:
>>> On Tue, Aug 17, 2021 at 3:49 AM Joerg Roedel <jroedel@xxxxxxx> wrote:
>>>>
>>>> Hi Marc,
>>>>
>>>> On Fri, Aug 13, 2021 at 11:44:39AM -0700, Marc Orr wrote:
>>>>> To date, we have _most_ x86 test cases (39/44) working under UEFI and
>>>>> we've also got some of the test cases to boot under SEV-ES, using the
>>>>> UEFI #VC handler.
>>>>
>>>> While the EFI APP approach simplifies the implementation a lot, I don't
>>>> think it is the best path to SEV and TDX testing for a couple of
>>>> reasons:
>>>>
>>>>         1) It leaves the details of #VC/#VE handling and the SEV-ES
>>>>            specific communication channels (GHCB) under control of the
>>>>            firmware. So we can't reliably test those interfaces from an
>>>>            EFI APP.
>>>>
>>>>         2) Same for the memory validation/acceptance interface needed
>>>>            for SEV-SNP and TDX. Using an EFI APP leaves those under
>>>>            firmware control and we are not able to reliably test them.
>>>>
>>>>         3) The IDT also stays under control of the firmware in an EFI
>>>>            APP, otherwise the firmware couldn't provide a #VC handler.
>>>>            This makes it unreliable to test anything IDT or IRQ related.
>>>>
>>>>         4) Relying on the firmware #VC hanlder limits the tests to its
>>>>            abilities. Implementing a separate #VC handler routine for
>>>>            kvm-unit-tests is more work, but it makes test development
>>>>            much more flexible.
>>>>
>>>> So it comes down to the fact that and EFI APP leaves control over
>>>> SEV/TDX specific hypervisor interfaces in the firmware, making it hard
>>>> and unreliable to test these interfaces from kvm-unit-tests. The stub
>>>> approach on the other side gives the tests full control over the VM,
>>>> allowing to test all aspects of the guest-host interface.
>>>
>>> I think we might be using terminology differently. (Maybe I mis-used
>>> the term “EFI app”?) With our approach, it is true that all
>>> pre-existing x86_64 test cases work out of the box with the UEFI #VC
>>> handler. However, because kvm-unit-tests calls `ExitBootServices` to
>>> take full control of the system it executes as a “UEFI-stubbed
>>> kernel”. Thus, it should be trivial for test cases to update the IDT
>>> to set up a custom #VC handler for the duration of a test. (Some of
>>> the x86_64 test cases already do something similar where they install
>>> a temporary exception handler and then restore the “default”
>>> kvm-unit-tests exception handler.)
>>>
>>> In general, our approach is to set up the test cases to run with the
>>> kvm-unit-tests configuration (e.g., IDT, GDT). The one exception is
>>> the #VC handler. However, all of this state can be overridden within a
>>> test as needed.
>>>
>>> Zixuan just posted the patches. So hopefully they make things more clear.
>>>
>>
>> Nomenclature aside, I believe Zixuan's patchset [1] takes the same approach
>> as I posted here. In the end, we need to:
>> - build the testcases as ELF shared objs and link them to look like a PE
>> - switch away from UEFI GDT/IDT/pagetable states on early boot to what
>>   kvm-unit-tests needs
>> - modify the testcases that contain non-PIC asm stubs to allow building
>>   them as shared objs
>>
>> I went with avoiding to bring in gnu-efi objects into kvm-unit-tests
>> for EFI helpers, and disabling the non-PIC testcases for the RFC's sake.
>>
>> I'll try out "x86 UEFI: Convert x86 test cases to PIC" [2] from Zixuan's
>> patchset with my series and see what breaks. I think we can combine
>> the two patchsets.
>>
>> [1] https://lore.kernel.org/r/20210818000905.1111226-1-zixuanwang@xxxxxxxxxx/
>> [2] https://lore.kernel.org/r/20210818000905.1111226-10-zixuanwang@xxxxxxxxxx/
> 
> This sounds great to us. We will also experiment with combining the
> two patchsets and report back when we have some experience with this.
> Though, please do also report back if you have an update on this
> before we do.
> 

I sent out a v2 [1] with Zixuan's "x86 UEFI: Convert x86 test cases to PIC" [2]
pulled in, PTAL.

[1] https://lore.kernel.org/r/20210819113400.26516-1-varad.gautam@xxxxxxxx/
[2] https://lore.kernel.org/r/20210818000905.1111226-10-zixuanwang@xxxxxxxxxx/

Thanks,
Varad

> Thanks,
> Marc
> 

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