Re: [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use

From: Vitaly Kuznetsov
Date: Tue Jun 25 2019 - 04:52:02 EST

Liran Alon <liran.alon@xxxxxxxxxx> writes:

>> On 24 Jun 2019, at 16:30, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>> +bool nested_enlightened_vmentry(struct kvm_vcpu *vcpu, u64 *evmptr)
> I prefer to rename evmptr to evmcs_ptr. I think itâs more readable and sufficiently short.
> In addition, I think you should return either -1ull or assist_page.current_nested_vmcs.
> i.e. Donât return evmcs_ptr by pointer but instead as a return-value
> and get rid of the bool.

Actually no, sorry, I'm having second thoughts here: in handle_vmclear()
we don't care about the value of evmcs_ptr, we only want to check that
enlightened vmentry bit is enabled in assist page. If we switch to
checking evmcs_ptr against '-1', for example, we will make '-1' a magic
value which is not in the TLFS. Windows may decide to use it for
something else - and we will get a hard-to-debug bug again.

If you still dislike nested_enlightened_vmentry() having the side effect
of fetching evmcs_ptr I can get rid of it by splitting the function into
two, however, it will be less efficient for
nested_vmx_handle_enlightened_vmptrld(). Or we can just leave things as
they are there and use the newly introduced function in handle_vmclear()