On Mon, Sep 20, 2021 at 6:27 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > On 27/08/21 05:12, Zixuan Wang wrote: > > + * > > + * This is because KVM-Unit-Tests reuses UEFI #VC handler that requires UEFI > > + * code and data segments to run. The UEFI #VC handler crashes the guest VM if > > + * these segments are not available. So we need to copy these two UEFI segments > > + * into KVM-Unit-Tests GDT. > > + * > > + * UEFI uses 0x30 as code segment and 0x38 as data segment. Fortunately, these > > + * segments can be safely overridden in KVM-Unit-Tests as they are used as > > + * protected mode and real mode segments (see x86/efi/efistart64.S for more > > + * details), which are not used in EFI set up process. > > Is 0x30/0x38 the same as kvm-unit-tests's 0x08/0x10? Can kvm-unit-tests > simply change its ring-0 64-bit CS/DS to 0x30 and 0x38 instead of 0x08 > and 0x10? I can help with that too, since there would be some more > shuffling to keep similar descriptors together: > > * 0x00 NULL descriptor NULL descriptor > * 0x08 intr_alt_stack TSS ring-0 code segment (32-bit) > * 0x10 (0x13) **unused** ring-3 code segment (64-bit) > * 0x18 ring-0 code segment (P=0) ring-0 code segment (64-bit, P=0) > * 0x20 ring-0 code segment (16-bit) same > * 0x28 ring-0 data segment (16-bit) same > * 0x30 ring-0 code segment (32-bit) ring-0 code segment (64-bit) > * 0x38 ring-0 data segment (32-bit) ring-0 data segment (32/64-bit) > * 0x40 (0x43) ring-3 code segment (32-bit) same > * 0x48 (0x4b) ring-3 data segment (32-bit) ring-3 data segment (32/64-bit) > * 0x50-0x78 free to use for test cases same > > or: > > old new > ---- ---- > 0x00 0x00 > 0x20 0x08 > 0x48 0x10 > 0x18 0x18 > 0x28 0x20 > 0x30 0x28 > 0x08 0x30 > 0x10 0x38 > 0x38 0x40 > 0x40 0x48 > > Thanks, > > Paolo > Thank you for the detailed explanation! Updating KVM-unit-tests GDT is one way to solve the problem, but we found a more straightforward solution [1]: We found it possible to update the 'code segment selector' field in the #VC IDT entry and point it to the KVM-unit-tests code segment. This allows the UEFI #VC handler to use KVM-unit-tests segments, and we do not need to copy the UEFI segments. I will update this into the next version. [1] https://github.com/TheNetAdmin/KVM-Unit-Tests-dev-fork/commit/ab480fd0fbad813c2922526a0bccadf121cb9240 Best regards, Zixuan
