Re: [PATCH v14 09/22] KVM: selftests: Expose functions to get default sregs values

[Xiaoyao Li]

On 7/23/2026 7:13 AM, Lisa Wang wrote:

From: Sagi Shahar <sa...@google.com>

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.

Reviewed-by: Binbin Wu <binbin...@linux.intel.com>
Signed-off-by: Sagi Shahar <sa...@google.com>
Reviewed-by: Ira Weiny <ira.we...@intel.com>
Signed-off-by: Lisa Wang <wyi...@google.com>

Reviewed-by: Xiaoyao Li <xiaoyao...@intel.com>

---
  .../testing/selftests/kvm/include/x86/processor.h  | 35 ++++++++++++++++++++++
  tools/testing/selftests/kvm/lib/x86/processor.c    | 20 ++++---------
  2 files changed, 41 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h 
b/tools/testing/selftests/kvm/include/x86/processor.h
index 76180dfaffea..7e00c9414595 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -29,6 +29,10 @@ extern u64 guest_tsc_khz;
  #define MAX_NR_CPUID_ENTRIES 100
  #endif

+#ifndef NUM_INTERRUPTS

+#define NUM_INTERRUPTS 256
+#endif
+
  #define NONCANONICAL 0xaaaaaaaaaaaaaaaaull

/* Forced emulation prefix, used to invoke the emulator unconditionally. */

@@ -1564,4 +1568,35 @@ u64 *tdp_get_pte(struct kvm_vm *vm, u64 l2_gpa);

bool sys_clocksource_is_based_on_tsc(void); +static inline u16 kvm_get_default_idt_limit(void)

+{
+       return NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
+}
+
+static inline u16 kvm_get_default_gdt_limit(void)
+{
+       return getpagesize() - 1;
+}
+
+static inline u64 kvm_get_default_cr0(void)
+{
+       return X86_CR0_PE | X86_CR0_NE | X86_CR0_PG;
+}
+
+static inline u64 kvm_get_default_cr4(int pgtable_levels)
+{
+       u64 cr4 = X86_CR4_PAE | X86_CR4_OSFXSR;
+
+       if (kvm_cpu_has(X86_FEATURE_XSAVE))
+               cr4 |= X86_CR4_OSXSAVE;
+       if (pgtable_levels == 5)
+               cr4 |= X86_CR4_LA57;
+       return cr4;
+}
+
+static inline u64 kvm_get_default_efer(void)
+{
+       return EFER_LME | EFER_LMA | EFER_NX;
+}
+
  #endif /* SELFTEST_KVM_PROCESSOR_H */
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c 
b/tools/testing/selftests/kvm/lib/x86/processor.c
index 97acc5aaf7b7..ad75e19bb3a2 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -15,10 +15,6 @@
  #include "tdx/tdx_util.h"
  #include "vmx.h"

-#ifndef NUM_INTERRUPTS

-#define NUM_INTERRUPTS 256
-#endif
-
  gva_t exception_handlers;
  bool host_cpu_is_amd;
  bool host_cpu_is_intel;
@@ -647,17 +643,13 @@ 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.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;
-       if (vm->mmu.pgtable_levels == 5)
-               sregs.cr4 |= X86_CR4_LA57;
-       sregs.efer |= (EFER_LME | EFER_LMA | EFER_NX);
+       sregs.gdt.limit = kvm_get_default_gdt_limit();
+
+       sregs.cr0 = kvm_get_default_cr0();
+       sregs.cr4 |= kvm_get_default_cr4(vm->mmu.pgtable_levels);
+       sregs.efer |= kvm_get_default_efer();

kvm_seg_set_unusable(&sregs.ldt);

        kvm_seg_set_kernel_code_64bit(&sregs.cs);