On Tue, Aug 26, 2025 at 3:14 PM Ira Weiny <ira.we...@intel.com> wrote:
>
> Sean Christopherson wrote:
> > On Wed, Aug 20, 2025, Sagi Shahar wrote:
> > > TDX require special handling for VM and VCPU initialization for various
> > > reasons:
> > > - Special ioctlss for creating VM and VCPU.
> > > - TDX registers are inaccessible to KVM.
> > > - TDX require special boot code trampoline for loading parameters.
> > > - TDX only supports KVM_CAP_SPLIT_IRQCHIP.
> >
> > Please split this up and elaborate at least a little bit on why each flow
> > needs
> > special handling for TDX. Even for someone like me who is fairly familiar
> > with
> > TDX, there's too much "Trust me bro" and not enough explanation of why
> > selftests
> > really need all of these special paths for TDX.
> >
> > At least four patches, one for each of your bullet points. Probably 5 or
> > 6, as
> > I think the CPUID handling warrants its own patch.
> >
> > > Hook this special handling into __vm_create() and vm_arch_vcpu_add()
> > > using the utility functions added in previous patches.
> > >
> > > Signed-off-by: Sagi Shahar <sa...@google.com>
> > > ---
> > > tools/testing/selftests/kvm/lib/kvm_util.c | 24 ++++++++-
> > > .../testing/selftests/kvm/lib/x86/processor.c | 49 ++++++++++++++-----
> > > 2 files changed, 61 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c
> > > b/tools/testing/selftests/kvm/lib/kvm_util.c
> > > index b4c8702ba4bd..d9f0ff97770d 100644
> > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > > @@ -4,6 +4,7 @@
> > > *
> > > * Copyright (C) 2018, Google LLC.
> > > */
> > > +#include "tdx/tdx_util.h"
> > > #include "test_util.h"
> > > #include "kvm_util.h"
> > > #include "processor.h"
> > > @@ -465,7 +466,7 @@ void kvm_set_files_rlimit(uint32_t nr_vcpus)
> > > static bool is_guest_memfd_required(struct vm_shape shape)
> > > {
> > > #ifdef __x86_64__
> > > - return shape.type == KVM_X86_SNP_VM;
> > > + return (shape.type == KVM_X86_SNP_VM || shape.type == KVM_X86_TDX_VM);
> > > #else
> > > return false;
> > > #endif
> > > @@ -499,6 +500,12 @@ struct kvm_vm *__vm_create(struct vm_shape shape,
> > > uint32_t nr_runnable_vcpus,
> > > for (i = 0; i < NR_MEM_REGIONS; i++)
> > > vm->memslots[i] = 0;
> > >
> > > + if (is_tdx_vm(vm)) {
> > > + /* Setup additional mem regions for TDX. */
> > > + vm_tdx_setup_boot_code_region(vm);
> > > + vm_tdx_setup_boot_parameters_region(vm, nr_runnable_vcpus);
> > > + }
> > > +
> > > kvm_vm_elf_load(vm, program_invocation_name);
> > >
> > > /*
> > > @@ -1728,11 +1735,26 @@ void *addr_gpa2alias(struct kvm_vm *vm,
> > > vm_paddr_t gpa)
> > > return (void *) ((uintptr_t) region->host_alias + offset);
> > > }
> > >
> > > +static bool is_split_irqchip_required(struct kvm_vm *vm)
> > > +{
> > > +#ifdef __x86_64__
> > > + return is_tdx_vm(vm);
> > > +#else
> > > + return false;
> > > +#endif
> > > +}
> > > +
> > > /* Create an interrupt controller chip for the specified VM. */
> > > void vm_create_irqchip(struct kvm_vm *vm)
> > > {
> > > int r;
> > >
> > > + if (is_split_irqchip_required(vm)) {
> > > + vm_enable_cap(vm, KVM_CAP_SPLIT_IRQCHIP, 24);
> > > + vm->has_irqchip = true;
> > > + return;
> > > + }
> >
> > Ugh. IMO, this is a KVM bug. Allowing KVM_CREATE_IRQCHIP for a TDX VM is
> > simply
> > wrong. It _can't_ work. Waiting until KVM_CREATE_VCPU to fail setup is
> > terrible
> > ABI.
> >
> > If we stretch the meaning of ENOTTY a bit and return that when trying to
> > create
> > a fully in-kernel IRQCHIP for a TDX VM, then the selftests code Just Works
> > thanks
> > to the code below, which handles the scenario where KVM was be built without
> ^^^^^^^^^^
>
> I'm not following. Was there supposed to be a patch attached?
>
I think Sean refers to the original implementation which was out of
the scope for the git diff so it was left out of the patch:
/*
* Allocate a fully in-kernel IRQ chip by default, but fall back to a
* split model (x86 only) if that fails (KVM x86 allows compiling out
* support for KVM_CREATE_IRQCHIP).
*/
r = __vm_ioctl(vm, KVM_CREATE_IRQCHIP, NULL);
if (r && errno == ENOTTY && kvm_has_cap(KVM_CAP_SPLIT_IRQCHIP))
vm_enable_cap(vm, KVM_CAP_SPLIT_IRQCHIP, 24);
else
TEST_ASSERT_VM_VCPU_IOCTL(!r, KVM_CREATE_IRQCHIP, r, vm);
/*
* Allocate a fully in-kernel IRQ chip by default, but fall back to a
* split model (x86 only) if that fails (KVM x86 allows compiling out
* support for KVM_CREATE_IRQCHIP).
*/
r = __vm_ioctl(vm, KVM_CREATE_IRQCHIP, NULL);
if (r && errno == ENOTTY && kvm_has_cap(KVM_CAP_SPLIT_IRQCHIP))
vm_enable_cap(vm, KVM_CAP_SPLIT_IRQCHIP, 24);
else
TEST_ASSERT_VM_VCPU_IOCTL(!r, KVM_CREATE_IRQCHIP, r, vm);
/*
* Allocate a fully in-kernel IRQ chip by default, but fall back to a
* split model (x86 only) if that fails (KVM x86 allows compiling out
* support for KVM_CREATE_IRQCHIP).
*/
r = __vm_ioctl(vm, KVM_CREATE_IRQCHIP, NULL);
if (r && errno == ENOTTY && kvm_has_cap(KVM_CAP_SPLIT_IRQCHIP))
vm_enable_cap(vm, KVM_CAP_SPLIT_IRQCHIP, 24);
else
TEST_ASSERT_VM_VCPU_IOCTL(!r, KVM_CREATE_IRQCHIP, r, vm);
> Ira
>
> > support for in-kernel I/O APIC (and PIC and PIT).
>
>
