linux-kernel - Re: [PATCH 3/4] KVM: x86: kvm_hv_flush

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Date:   Thu, 8 Apr 2021 14:37:45 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>
Cc:     Alexander Graf <graf@...zon.com>,
        Evgeny Iakovlev <eyakovl@...zon.de>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 3/4] KVM: x86: kvm_hv_flush_tlb use inputs from XMM
 registers

On 08/04/21 14:01, Vitaly Kuznetsov wrote:
> 
> Also, we can probably defer kvm_hv_hypercall_read_xmm() until we know
> how many regs we actually need to not read them all (we will always
> need xmm[0] I guess so we can as well read it here).

The cost is get/put FPU, so I think there's not much to gain from that.

Paolo