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

[Binbin Wu <binbin.wu@linux.intel.com>]

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 <sagis@google.com>

Reviewed-by: Binbin Wu <binbin.wu@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);