Re: [PATCH v10 02/21] KVM: selftests: Expose functions to get default sregs values

[Binbin Wu]

On 9/4/2025 2:54 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>

Reviewed-by: Binbin Wu <binbin...@linux.intel.com>

One suggestion:
It's better to add change history so that reviewers can know the change quickly
without comparing b/t versions.

---
  .../selftests/kvm/include/x86/processor.h     | 33 +++++++++++++++++++
  .../testing/selftests/kvm/lib/x86/processor.c | 12 +++----
  2 files changed, 38 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..f610c09cadf4 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -27,6 +27,10 @@ extern uint64_t 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. */

@@ -1456,4 +1460,33 @@ void virt_map_level(struct kvm_vm *vm, uint64_t vaddr, 
uint64_t paddr,

bool sys_clocksource_is_based_on_tsc(void); +static inline uint16_t kvm_get_default_idt_limit(void)

+{
+       return NUM_INTERRUPTS * sizeof(struct idt_entry) - 1;
+}
+
+static inline uint16_t kvm_get_default_gdt_limit(void)
+{
+       return getpagesize() - 1;
+}
+
+static inline uint64_t kvm_get_default_cr0(void)
+{
+       return X86_CR0_PE | X86_CR0_NE | X86_CR0_PG;
+}
+
+static inline 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;
+}
+
+static inline uint64_t 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 d4c19ac885a9..83efcf48faad 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -498,15 +498,13 @@ 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);