Re: [kvm-unit-tests PATCH] nVMX: Fix testing failure for canonical checks when forced emulation is not available

[Sean Christopherson <seanjc@xxxxxxxxxx>]

On Fri, May 23, 2025, Chenyi Qiang wrote:
> Use the _safe() variant instead of _fep_safe() to avoid failure if the
> forced emulated is not available.
> 
> Fixes: 05fbb364b5b2 ("nVMX: add a test for canonical checks of various host state vmcs12 fields")
> Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> ---
>  x86/vmx_tests.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
> index 2f178227..01a15b7c 100644
> --- a/x86/vmx_tests.c
> +++ b/x86/vmx_tests.c
> @@ -10881,12 +10881,11 @@ static int set_host_value(u64 vmcs_field, u64 value)
>  	case HOST_BASE_GDTR:
>  		sgdt(&dt_ptr);
>  		dt_ptr.base = value;
> -		lgdt(&dt_ptr);
> -		return lgdt_fep_safe(&dt_ptr);
> +		return lgdt_safe(&dt_ptr);
>  	case HOST_BASE_IDTR:
>  		sidt(&dt_ptr);
>  		dt_ptr.base = value;
> -		return lidt_fep_safe(&dt_ptr);
> +		return lidt_safe(&dt_ptr);

Hmm, the main purpose of this particular test is to verify KVM's emulation of the
canonical checks, so it probably makes sense to force emulation when possible.

It's not the most performant approach, but how about this?

diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index 2f178227..fe53e989 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -10881,12 +10881,13 @@ static int set_host_value(u64 vmcs_field, u64 value)
        case HOST_BASE_GDTR:
                sgdt(&dt_ptr);
                dt_ptr.base = value;
-               lgdt(&dt_ptr);
-               return lgdt_fep_safe(&dt_ptr);
+               return is_fep_available() ? lgdt_fep_safe(&dt_ptr) :
+                                           lgdt_safe(&dt_ptr);
        case HOST_BASE_IDTR:
                sidt(&dt_ptr);
                dt_ptr.base = value;
-               return lidt_fep_safe(&dt_ptr);
+               return is_fep_available() ? lidt_fep_safe(&dt_ptr) :
+                                           lidt_safe(&dt_ptr);
        case HOST_BASE_TR:
                /* Set the base and clear the busy bit */
                set_gdt_entry(FIRST_SPARE_SEL, value, 0x200, 0x89, 0);