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/ Thanks, Varad > Thanks, > Marc > -- SUSE Software Solutions Germany GmbH Maxfeldstr. 5 90409 Nürnberg Germany HRB 36809, AG Nürnberg Geschäftsführer: Felix Imendörffer
