Re: [PATCH v9 03/19] KVM: selftests: Expose functions to get default sregs values

[Binbin Wu]

On 8/21/2025 12:28 PM, Sagi Shahar wrote:

TDX can't set sregs values directly using KVM_SET_SREGS. Expose the
default values of certain sregs used by TDX VMs so they can be set
manually.

Signed-off-by: Sagi Shahar <sa...@google.com>
---
  .../selftests/kvm/include/x86/processor.h     |  6 +++
  .../testing/selftests/kvm/lib/x86/processor.c | 41 +++++++++++++++----
  2 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h 
b/tools/testing/selftests/kvm/include/x86/processor.h
index 2efb05c2f2fb..5c16507f9b2d 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1026,6 +1026,12 @@ static inline struct kvm_cpuid2 *allocate_kvm_cpuid2(int 
nr_entries)

void vcpu_init_cpuid(struct kvm_vcpu *vcpu, const struct kvm_cpuid2 *cpuid); +uint16_t kvm_get_default_idt_limit(void);

+uint16_t kvm_get_default_gdt_limit(void);
+uint64_t kvm_get_default_cr0(void);
+uint64_t kvm_get_default_cr4(void);
+uint64_t kvm_get_default_efer(void);

Can these be defined in the header file as static inline?

+
  static inline void vcpu_get_cpuid(struct kvm_vcpu *vcpu)
  {
        vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c 
b/tools/testing/selftests/kvm/lib/x86/processor.c
index d4c19ac885a9..b2a4b11ac8c0 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -488,6 +488,35 @@ static void kvm_seg_set_tss_64bit(vm_vaddr_t base, struct 
kvm_segment *segp)
        segp->present = 1;
  }

+uint16_t kvm_get_default_idt_limit(void)

+{
+       return NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
+}
+
+uint16_t kvm_get_default_gdt_limit(void)
+{
+       return getpagesize() - 1;
+}
+
+uint64_t kvm_get_default_cr0(void)
+{
+       return X86_CR0_PE | X86_CR0_NE | X86_CR0_PG;
+}
+
+uint64_t kvm_get_default_cr4(void)
+{
+       uint64_t cr4 = X86_CR4_PAE | X86_CR4_OSFXSR;
+
+       if (kvm_cpu_has(X86_FEATURE_XSAVE))
+               cr4 |= X86_CR4_OSXSAVE;
+       return cr4;
+}
+
+uint64_t kvm_get_default_efer(void)
+{
+       return EFER_LME | EFER_LMA | EFER_NX;
+}
+
  static void vcpu_init_sregs(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
  {
        struct kvm_sregs sregs;
@@ -498,15 +527,13 @@ static void vcpu_init_sregs(struct kvm_vm *vm, struct 
kvm_vcpu *vcpu)
        vcpu_sregs_get(vcpu, &sregs);

sregs.idt.base = vm->arch.idt;

-       sregs.idt.limit = NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
+       sregs.idt.limit = kvm_get_default_idt_limit();
        sregs.gdt.base = vm->arch.gdt;
-       sregs.gdt.limit = getpagesize() - 1;
+       sregs.gdt.limit = kvm_get_default_gdt_limit();

- sregs.cr0 = X86_CR0_PE | X86_CR0_NE | X86_CR0_PG;

-       sregs.cr4 |= X86_CR4_PAE | X86_CR4_OSFXSR;
-       if (kvm_cpu_has(X86_FEATURE_XSAVE))
-               sregs.cr4 |= X86_CR4_OSXSAVE;
-       sregs.efer |= (EFER_LME | EFER_LMA | EFER_NX);
+       sregs.cr0 = kvm_get_default_cr0();
+       sregs.cr4 |= kvm_get_default_cr4();
+       sregs.efer |= kvm_get_default_efer();

kvm_seg_set_unusable(&sregs.ldt);

        kvm_seg_set_kernel_code_64bit(&sregs.cs);