Re: [PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features() for KVM

[Paolo Bonzini]

On 1/5/22 13:35, Yang Zhong wrote:
> +int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
> +{
> +	lockdep_assert_preemption_enabled();
> +

The old fpu_update_guest_perm_features(guest_fpu) is equivalent to

	fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);

Missing doc comment:

/*
 * fpu_enable_guest_xfd_features - Enable xfeatures according to guest perm
 * @guest_fpu:         Pointer to the guest FPU container
 * @xfeatures:         Features requested by guest CPUID
 *
 * Enable all dynamic xfeatures according to guest perm and requested CPUID.
 * Invoked if the caller wants to conservatively expand fpstate buffer instead
 * of waiting until XCR0 or XFD MSR is written.
 *
 * Return: 0 on success, error code otherwise
 */

Also, the check for 32-bit is slightly imprecise:

	/* Dynamic xfeatures are not supported with 32-bit kernels. */
	if (!IS_ENABLED(CONFIG_X86_64))
-		return 0;
+		return -EINVAL;

since we only get here with xfeatures != 0 (if it compiles, just removing
the IS_ENABLED check altogether would be even better).  With these changes,

Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Thanks,

Paolo