linux-kernel - Re: [PATCH] KVM/X86: Check input sreg values before loading vcpu

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Message-ID: <20180308161536.GH12290@flask>
Date:   Thu, 8 Mar 2018 17:15:36 +0100
From:   "rkrcmar@...hat.com" <rkrcmar@...hat.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
Cc:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM/X86: Check input sreg values before loading vcpu

2018-02-27 06:57+0000, Tianyu Lan:
> From: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> 
> This patch is to check sreg value first and then load vcpu in order
> to avoid redundant loading/putting vcpu.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> ---

Patch "KVM: x86: KVM_CAP_SYNC_REGS" made significant changes to the
sregs setter, so the patch cannot be applied in current form.

I think that moving the X86_CR4_OSXSAVE check to guest_cpuid_has still
makes sense, but avoiding the vcpu_load/put would produce worse code
elsewhere and avoiding the load/put is not critical as any error is
probably going to be the end for this VM.

Thanks.