From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v2 6/6] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case
Date: Wed, 25 Jul 2018 10:37:43 +0200
Message-ID: <87va93pv6w.fsf@vitty.brq.redhat.com>
References: <20180621123046.29606-1-vkuznets@redhat.com>
        <20180621123046.29606-7-vkuznets@redhat.com>
        <a826fd88-0199-8e7b-ebfc-290e936b5efc@redhat.com>
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Cc: kvm@vger.kernel.org,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Roman Kagan <rkagan@virtuozzo.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
        Mohammed Gamal <mmorsy@redhat.com>,
        Cathy Avery <cavery@redhat.com>, linux-kernel@vger.kernel.org,
        Jim Mattson <jmattson@google.com>,
        Liran Alon <liran.alon@oracle.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <a826fd88-0199-8e7b-ebfc-290e936b5efc@redhat.com> (Paolo
        Bonzini's message of "Tue, 24 Jul 2018 19:09:04 +0200")
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 21/06/2018 14:30, Vitaly Kuznetsov wrote:
>> +static __always_inline bool evmcs_needs_write(struct vcpu_vmx *vmx,
>> +					      u16 clean_field)
>> +{
>> +	if (vmx->nested.dirty_vmcs12)
>> +		return true;
>
> Why is this needed?  If it weren't for it, you could pass hv_evmcs
> directly to evmcs_needs_write, which would simplify the code a bit in
> the caller.

This is an equivalent of prepare_vmcs02()/prepare_vmcs02_full() split
for eVMCS case: when we switch from L2 guest A to L2 guest B we need to
write the whole VMCS so evmcs_needs_write() needs to return true.

We can, however, make an optimisation: forcefuly reset hv_clean_fields
mask on enlightened vmptrld making 'dirty_vmcs12' check redundant.

This series was posted quite some time ago, I'll rebase and re-test with
the fix included.

Thanks!

-- 
  Vitaly