Re: [RFC PATCH v5 04/29] KVM: selftests: Refactor steps in vCPU descriptor table initialization

[Sagi Shahar <sagis@google.com>]

On Tue, Feb 20, 2024 at 11:43 PM Binbin Wu <binbin.wu@linux.intel.com> wrote:
>
>
>
> On 12/13/2023 4:46 AM, Sagi Shahar wrote:
> > From: Ackerley Tng <ackerleytng@google.com>
> >
> > Split the vCPU descriptor table initialization process into a few
> > steps and expose them:
> >
> > + Setting up the IDT
> > + Syncing exception handlers into the guest
> >
> > In kvm_setup_idt(), we conditionally allocate guest memory for vm->idt
> > to avoid double allocation when kvm_setup_idt() is used after
> > vm_init_descriptor_tables().
> >
> > Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> > Signed-off-by: Ryan Afranji <afranji@google.com>
> > Signed-off-by: Sagi Shahar <sagis@google.com>
> > ---
> >   .../selftests/kvm/include/x86_64/processor.h  |  2 ++
> >   .../selftests/kvm/lib/x86_64/processor.c      | 19 ++++++++++++++++---
> >   2 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
> > index 0b8855d68744..5c4e9a27d9e2 100644
> > --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> > +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> > @@ -1089,6 +1089,8 @@ struct idt_entry {
> >       uint32_t offset2; uint32_t reserved;
> >   };
> >
> > +void kvm_setup_idt(struct kvm_vm *vm, struct kvm_dtable *dt);
> > +void sync_exception_handlers_to_guest(struct kvm_vm *vm);
> >   void vm_init_descriptor_tables(struct kvm_vm *vm);
> >   void vcpu_init_descriptor_tables(struct kvm_vcpu *vcpu);
> >   void vm_install_exception_handler(struct kvm_vm *vm, int vector,
> > diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > index b6b9438e0a33..566d82829da4 100644
> > --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> > @@ -1155,19 +1155,32 @@ void vm_init_descriptor_tables(struct kvm_vm *vm)
> >                       DEFAULT_CODE_SELECTOR);
> >   }
> >
> > +void kvm_setup_idt(struct kvm_vm *vm, struct kvm_dtable *dt)
> > +{
> > +     if (!vm->idt)
> > +             vm->idt = vm_vaddr_alloc_page(vm);
>
> IDT is allocated in DATA memslot in current code, but here, when using
> vm_vaddr_alloc_page(), it will be allocated in TEST_DATA memslot.
>
> Do we need to follow the current code to use
> __vm_vaddr_alloc_page(vm, MEM_REGION_DATA) instead?

This code is no longer needed after Sean's refactor in
"[PATCH 00/18] KVM: selftests: Clean up x86's DT initialization"
https://lore.kernel.org/lkml/20240314232637.2538648-1-seanjc@google.com/

>
> > +
> > +     dt->base = vm->idt;
> > +     dt->limit = NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
> > +}
> > +
> > +void sync_exception_handlers_to_guest(struct kvm_vm *vm)
> > +{
> > +     *(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
> > +}
> > +
> >   void vcpu_init_descriptor_tables(struct kvm_vcpu *vcpu)
> >   {
> >       struct kvm_vm *vm = vcpu->vm;
> >       struct kvm_sregs sregs;
> >
> >       vcpu_sregs_get(vcpu, &sregs);
> > -     sregs.idt.base = vm->idt;
> > -     sregs.idt.limit = NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
> > +     kvm_setup_idt(vcpu->vm, &sregs.idt);
> >       sregs.gdt.base = vm->gdt;
> >       sregs.gdt.limit = getpagesize() - 1;
> >       kvm_seg_set_kernel_data_64bit(NULL, DEFAULT_DATA_SELECTOR, &sregs.gs);
> >       vcpu_sregs_set(vcpu, &sregs);
> > -     *(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
> > +     sync_exception_handlers_to_guest(vm);
> >   }
> >
> >   void vm_install_exception_handler(struct kvm_vm *vm, int vector,
>