linux-kernel - [RESEND] Atomic switch of MSR_IA32_UMWAIT

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Message-ID: <20200123154526.GC13178@linux.intel.com>
Date:   Thu, 23 Jan 2020 07:45:27 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Tao Xu <tao3.xu@...el.com>, Jingqi Liu <jingqi.liu@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RESEND] Atomic switch of MSR_IA32_UMWAIT_CONTROL

cc'ing KVM and LKML this time...

Why does KVM use the atomic load/store lists to load MSR_IA32_UMWAIT_CONTROL
on VM-Enter/VM-Exit?  Unless the host kernel is doing UWMAIT, which it
really shouldn't and AFAICT doesn't, isn't it better to use the shared MSR
mechanism to load the host value only when returning to userspace, and
reload the guest value on demand?