Re: [kvm PATCH v6 2/2] kvm: x86: Dynamically allocate guest_fpu

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On 10/31/18 4:49 PM, Marc Orr wrote:
> +	if (!boot_cpu_has(X86_FEATURE_FPU) || !boot_cpu_has(X86_FEATURE_FXSR)) {
> +		printk(KERN_ERR "kvm: inadequate fpu\n");
> +		r = -EOPNOTSUPP;
> +		goto out;
> +	}

It would be nice to have a comment about _why_ this is inadequate.

>  	r = -ENOMEM;
> +	x86_fpu_cache = kmem_cache_create_usercopy(
> +				"x86_fpu",

For now, this should probably be kvm_x86_fpu since it's not used as a
generic x86 thing, yet.

Also, why is this a "usercopy"?  "fpu_kernel_xstate_size" includes (or
will soon include) supervisor state which can never be copied to
userspace.  If this structure is going out to userspace, that tells me
we might instead want fpu_user_xstate_size, *or* we want the
non-usercopy variant.




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