Re: [PATCH v6 56/60] i386/tdx: Don't treat SYSCALL as unavailable

Paolo Bonzini
2024-11-05T09:59:45Z

On 11/5/24 07:24, Xiaoyao Li wrote:
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> target/i386/kvm/tdx.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 9cb099e160e4..05475edf72bd 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c
> @@ -734,6 +734,13 @@ static int tdx_check_features(X86ConfidentialGuest *cg, CPUState *cs)
>
> requested = env->features[w];
> unavailable = requested & ~actual;
> + /*
> + * Intel enumerates SYSCALL bit as 1 only when processor in 64-bit
> + * mode and before vcpu running it's not in 64-bit mode.
> + */
> + if (w == FEAT_8000_0001_EDX && unavailable & CPUID_EXT2_SYSCALL) {
> + unavailable &= ~CPUID_EXT2_SYSCALL;
> + }
> mark_unavailable_features(cpu, w, unavailable, unav_prefix);
> if (unavailable) {
> mismatch = true;

This seems like a TDX module bug? It's the kind of thing that I guess
could be worked around in KVM.

If we do it in QEMU, I'd rather see it as

actual = cpuid_entry_get_reg(entry, wi->cpuid.reg);
switch (w) {
case FEAT_8000_0001_EDX:
actual |= CPUID_EXT2_SYSCALL;
break;
}
break;

Paolo